This section dives into the details of Spring Boot. Here you can learn about the key features that you may want to use and customize. If you have not already done so, you might want to read the "Getting Started" and "Developing with Spring Boot" sections, so that you have a good grounding of the basics.
1. SpringApplication
The SpringApplication
class provides a convenient way to bootstrap a Spring application that is started from a main()
method.
In many situations, you can delegate to the static SpringApplication.run
method, as shown in the following example:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args)
}
When your application starts, you should see something similar to the following output:
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.7.9) 2023-02-23 08:16:22.732 INFO 16686 --- [ main] o.s.b.d.f.s.MyApplication : Starting MyApplication using Java 1.8.0_362 on myhost with PID 16686 (/opt/apps/myapp.jar started by myuser in /opt/apps/) 2023-02-23 08:16:22.736 INFO 16686 --- [ main] o.s.b.d.f.s.MyApplication : No active profile set, falling back to 1 default profile: "default" 2023-02-23 08:16:23.684 INFO 16686 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http) 2023-02-23 08:16:23.696 INFO 16686 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2023-02-23 08:16:23.697 INFO 16686 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.71] 2023-02-23 08:16:23.782 INFO 16686 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2023-02-23 08:16:23.782 INFO 16686 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 997 ms 2023-02-23 08:16:24.158 INFO 16686 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '' 2023-02-23 08:16:24.169 INFO 16686 --- [ main] o.s.b.d.f.s.MyApplication : Started MyApplication in 1.853 seconds (JVM running for 2.236)
By default, INFO
logging messages are shown, including some relevant startup details, such as the user that launched the application.
If you need a log level other than INFO
, you can set it, as described in Log Levels.
The application version is determined using the implementation version from the main application class’s package.
Startup information logging can be turned off by setting spring.main.log-startup-info
to false
.
This will also turn off logging of the application’s active profiles.
To add additional logging during startup, you can override logStartupInfo(boolean) in a subclass of SpringApplication .
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1.1. Startup Failure
If your application fails to start, registered FailureAnalyzers
get a chance to provide a dedicated error message and a concrete action to fix the problem.
For instance, if you start a web application on port 8080
and that port is already in use, you should see something similar to the following message:
*************************** APPLICATION FAILED TO START *************************** Description: Embedded servlet container failed to start. Port 8080 was already in use. Action: Identify and stop the process that is listening on port 8080 or configure this application to listen on another port.
Spring Boot provides numerous FailureAnalyzer implementations, and you can add your own.
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If no failure analyzers are able to handle the exception, you can still display the full conditions report to better understand what went wrong.
To do so, you need to enable the debug
property or enable DEBUG
logging for org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
.
For instance, if you are running your application by using java -jar
, you can enable the debug
property as follows:
$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug
1.2. Lazy Initialization
SpringApplication
allows an application to be initialized lazily.
When lazy initialization is enabled, beans are created as they are needed rather than during application startup.
As a result, enabling lazy initialization can reduce the time that it takes your application to start.
In a web application, enabling lazy initialization will result in many web-related beans not being initialized until an HTTP request is received.
A downside of lazy initialization is that it can delay the discovery of a problem with the application. If a misconfigured bean is initialized lazily, a failure will no longer occur during startup and the problem will only become apparent when the bean is initialized. Care must also be taken to ensure that the JVM has sufficient memory to accommodate all of the application’s beans and not just those that are initialized during startup. For these reasons, lazy initialization is not enabled by default and it is recommended that fine-tuning of the JVM’s heap size is done before enabling lazy initialization.
Lazy initialization can be enabled programmatically using the lazyInitialization
method on SpringApplicationBuilder
or the setLazyInitialization
method on SpringApplication
.
Alternatively, it can be enabled using the spring.main.lazy-initialization
property as shown in the following example:
spring.main.lazy-initialization=true
spring:
main:
lazy-initialization: true
If you want to disable lazy initialization for certain beans while using lazy initialization for the rest of the application, you can explicitly set their lazy attribute to false using the @Lazy(false) annotation.
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1.3. Customizing the Banner
The banner that is printed on start up can be changed by adding a banner.txt
file to your classpath or by setting the spring.banner.location
property to the location of such a file.
If the file has an encoding other than UTF-8, you can set spring.banner.charset
.
In addition to a text file, you can also add a banner.gif
, banner.jpg
, or banner.png
image file to your classpath or set the spring.banner.image.location
property.
Images are converted into an ASCII art representation and printed above any text banner.
Inside your banner.txt
file, you can use any key available in the Environment
as well as any of the following placeholders:
Variable | Description |
---|---|
|
The version number of your application, as declared in |
|
The version number of your application, as declared in |
|
The Spring Boot version that you are using.
For example |
|
The Spring Boot version that you are using, formatted for display (surrounded with brackets and prefixed with |
|
Where |
|
The title of your application, as declared in |
The SpringApplication.setBanner(…) method can be used if you want to generate a banner programmatically.
Use the org.springframework.boot.Banner interface and implement your own printBanner() method.
|
You can also use the spring.main.banner-mode
property to determine if the banner has to be printed on System.out
(console
), sent to the configured logger (log
), or not produced at all (off
).
The printed banner is registered as a singleton bean under the following name: springBootBanner
.
The This is why we recommend that you always launch unpacked jars using |
1.4. Customizing SpringApplication
If the SpringApplication
defaults are not to your taste, you can instead create a local instance and customize it.
For example, to turn off the banner, you could write:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(MyApplication.class);
application.setBannerMode(Banner.Mode.OFF);
application.run(args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args) {
setBannerMode(Banner.Mode.OFF)
}
}
The constructor arguments passed to SpringApplication are configuration sources for Spring beans.
In most cases, these are references to @Configuration classes, but they could also be direct references @Component classes.
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It is also possible to configure the SpringApplication
by using an application.properties
file.
See Externalized Configuration for details.
For a complete list of the configuration options, see the SpringApplication
Javadoc.
1.5. Fluent Builder API
If you need to build an ApplicationContext
hierarchy (multiple contexts with a parent/child relationship) or if you prefer using a “fluent” builder API, you can use the SpringApplicationBuilder
.
The SpringApplicationBuilder
lets you chain together multiple method calls and includes parent
and child
methods that let you create a hierarchy, as shown in the following example:
new SpringApplicationBuilder()
.sources(Parent.class)
.child(Application.class)
.bannerMode(Banner.Mode.OFF)
.run(args);
SpringApplicationBuilder()
.sources(Parent::class.java)
.child(Application::class.java)
.bannerMode(Banner.Mode.OFF)
.run(*args)
There are some restrictions when creating an ApplicationContext hierarchy.
For example, Web components must be contained within the child context, and the same Environment is used for both parent and child contexts.
See the SpringApplicationBuilder Javadoc for full details.
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1.6. Application Availability
When deployed on platforms, applications can provide information about their availability to the platform using infrastructure such as Kubernetes Probes. Spring Boot includes out-of-the box support for the commonly used “liveness” and “readiness” availability states. If you are using Spring Boot’s “actuator” support then these states are exposed as health endpoint groups.
In addition, you can also obtain availability states by injecting the ApplicationAvailability
interface into your own beans.
1.6.1. Liveness State
The “Liveness” state of an application tells whether its internal state allows it to work correctly, or recover by itself if it is currently failing. A broken “Liveness” state means that the application is in a state that it cannot recover from, and the infrastructure should restart the application.
In general, the "Liveness" state should not be based on external checks, such as Health checks. If it did, a failing external system (a database, a Web API, an external cache) would trigger massive restarts and cascading failures across the platform. |
The internal state of Spring Boot applications is mostly represented by the Spring ApplicationContext
.
If the application context has started successfully, Spring Boot assumes that the application is in a valid state.
An application is considered live as soon as the context has been refreshed, see Spring Boot application lifecycle and related Application Events.
1.6.2. Readiness State
The “Readiness” state of an application tells whether the application is ready to handle traffic.
A failing “Readiness” state tells the platform that it should not route traffic to the application for now.
This typically happens during startup, while CommandLineRunner
and ApplicationRunner
components are being processed, or at any time if the application decides that it is too busy for additional traffic.
An application is considered ready as soon as application and command-line runners have been called, see Spring Boot application lifecycle and related Application Events.
Tasks expected to run during startup should be executed by CommandLineRunner and ApplicationRunner components instead of using Spring component lifecycle callbacks such as @PostConstruct .
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1.6.3. Managing the Application Availability State
Application components can retrieve the current availability state at any time, by injecting the ApplicationAvailability
interface and calling methods on it.
More often, applications will want to listen to state updates or update the state of the application.
For example, we can export the "Readiness" state of the application to a file so that a Kubernetes "exec Probe" can look at this file:
@Component
public class MyReadinessStateExporter {
@EventListener
public void onStateChange(AvailabilityChangeEvent<ReadinessState> event) {
switch (event.getState()) {
case ACCEPTING_TRAFFIC:
// create file /tmp/healthy
break;
case REFUSING_TRAFFIC:
// remove file /tmp/healthy
break;
}
}
}
@Component
class MyReadinessStateExporter {
@EventListener
fun onStateChange(event: AvailabilityChangeEvent<ReadinessState?>) {
when (event.state) {
ReadinessState.ACCEPTING_TRAFFIC -> {
// create file /tmp/healthy
}
ReadinessState.REFUSING_TRAFFIC -> {
// remove file /tmp/healthy
}
else -> {
// ...
}
}
}
}
We can also update the state of the application, when the application breaks and cannot recover:
@Component
public class MyLocalCacheVerifier {
private final ApplicationEventPublisher eventPublisher;
public MyLocalCacheVerifier(ApplicationEventPublisher eventPublisher) {
this.eventPublisher = eventPublisher;
}
public void checkLocalCache() {
try {
// ...
}
catch (CacheCompletelyBrokenException ex) {
AvailabilityChangeEvent.publish(this.eventPublisher, ex, LivenessState.BROKEN);
}
}
}
@Component
class MyLocalCacheVerifier(private val eventPublisher: ApplicationEventPublisher) {
fun checkLocalCache() {
try {
// ...
} catch (ex: CacheCompletelyBrokenException) {
AvailabilityChangeEvent.publish(eventPublisher, ex, LivenessState.BROKEN)
}
}
}
Spring Boot provides Kubernetes HTTP probes for "Liveness" and "Readiness" with Actuator Health Endpoints. You can get more guidance about deploying Spring Boot applications on Kubernetes in the dedicated section.
1.7. Application Events and Listeners
In addition to the usual Spring Framework events, such as ContextRefreshedEvent
, a SpringApplication
sends some additional application events.
Some events are actually triggered before the If you want those listeners to be registered automatically, regardless of the way the application is created, you can add a org.springframework.context.ApplicationListener=com.example.project.MyListener |
Application events are sent in the following order, as your application runs:
-
An
ApplicationStartingEvent
is sent at the start of a run but before any processing, except for the registration of listeners and initializers. -
An
ApplicationEnvironmentPreparedEvent
is sent when theEnvironment
to be used in the context is known but before the context is created. -
An
ApplicationContextInitializedEvent
is sent when theApplicationContext
is prepared and ApplicationContextInitializers have been called but before any bean definitions are loaded. -
An
ApplicationPreparedEvent
is sent just before the refresh is started but after bean definitions have been loaded. -
An
ApplicationStartedEvent
is sent after the context has been refreshed but before any application and command-line runners have been called. -
An
AvailabilityChangeEvent
is sent right after withLivenessState.CORRECT
to indicate that the application is considered as live. -
An
ApplicationReadyEvent
is sent after any application and command-line runners have been called. -
An
AvailabilityChangeEvent
is sent right after withReadinessState.ACCEPTING_TRAFFIC
to indicate that the application is ready to service requests. -
An
ApplicationFailedEvent
is sent if there is an exception on startup.
The above list only includes SpringApplicationEvent
s that are tied to a SpringApplication
.
In addition to these, the following events are also published after ApplicationPreparedEvent
and before ApplicationStartedEvent
:
-
A
WebServerInitializedEvent
is sent after theWebServer
is ready.ServletWebServerInitializedEvent
andReactiveWebServerInitializedEvent
are the servlet and reactive variants respectively. -
A
ContextRefreshedEvent
is sent when anApplicationContext
is refreshed.
You often need not use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks. |
Event listeners should not run potentially lengthy tasks as they execute in the same thread by default. Consider using application and command-line runners instead. |
Application events are sent by using Spring Framework’s event publishing mechanism.
Part of this mechanism ensures that an event published to the listeners in a child context is also published to the listeners in any ancestor contexts.
As a result of this, if your application uses a hierarchy of SpringApplication
instances, a listener may receive multiple instances of the same type of application event.
To allow your listener to distinguish between an event for its context and an event for a descendant context, it should request that its application context is injected and then compare the injected context with the context of the event.
The context can be injected by implementing ApplicationContextAware
or, if the listener is a bean, by using @Autowired
.
1.8. Web Environment
A SpringApplication
attempts to create the right type of ApplicationContext
on your behalf.
The algorithm used to determine a WebApplicationType
is the following:
-
If Spring MVC is present, an
AnnotationConfigServletWebServerApplicationContext
is used -
If Spring MVC is not present and Spring WebFlux is present, an
AnnotationConfigReactiveWebServerApplicationContext
is used -
Otherwise,
AnnotationConfigApplicationContext
is used
This means that if you are using Spring MVC and the new WebClient
from Spring WebFlux in the same application, Spring MVC will be used by default.
You can override that easily by calling setWebApplicationType(WebApplicationType)
.
It is also possible to take complete control of the ApplicationContext
type that is used by calling setApplicationContextClass(…)
.
It is often desirable to call setWebApplicationType(WebApplicationType.NONE) when using SpringApplication within a JUnit test.
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1.9. Accessing Application Arguments
If you need to access the application arguments that were passed to SpringApplication.run(…)
, you can inject a org.springframework.boot.ApplicationArguments
bean.
The ApplicationArguments
interface provides access to both the raw String[]
arguments as well as parsed option
and non-option
arguments, as shown in the following example:
@Component
public class MyBean {
public MyBean(ApplicationArguments args) {
boolean debug = args.containsOption("debug");
List<String> files = args.getNonOptionArgs();
if (debug) {
System.out.println(files);
}
// if run with "--debug logfile.txt" prints ["logfile.txt"]
}
}
@Component
class MyBean(args: ApplicationArguments) {
init {
val debug = args.containsOption("debug")
val files = args.nonOptionArgs
if (debug) {
println(files)
}
// if run with "--debug logfile.txt" prints ["logfile.txt"]
}
}
Spring Boot also registers a CommandLinePropertySource with the Spring Environment .
This lets you also inject single application arguments by using the @Value annotation.
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1.10. Using the ApplicationRunner or CommandLineRunner
If you need to run some specific code once the SpringApplication
has started, you can implement the ApplicationRunner
or CommandLineRunner
interfaces.
Both interfaces work in the same way and offer a single run
method, which is called just before SpringApplication.run(…)
completes.
This contract is well suited for tasks that should run after application startup but before it starts accepting traffic. |
The CommandLineRunner
interfaces provides access to application arguments as a string array, whereas the ApplicationRunner
uses the ApplicationArguments
interface discussed earlier.
The following example shows a CommandLineRunner
with a run
method:
@Component
public class MyCommandLineRunner implements CommandLineRunner {
@Override
public void run(String... args) {
// Do something...
}
}
@Component
class MyCommandLineRunner : CommandLineRunner {
override fun run(vararg args: String) {
// Do something...
}
}
If several CommandLineRunner
or ApplicationRunner
beans are defined that must be called in a specific order, you can additionally implement the org.springframework.core.Ordered
interface or use the org.springframework.core.annotation.Order
annotation.
1.11. Application Exit
Each SpringApplication
registers a shutdown hook with the JVM to ensure that the ApplicationContext
closes gracefully on exit.
All the standard Spring lifecycle callbacks (such as the DisposableBean
interface or the @PreDestroy
annotation) can be used.
In addition, beans may implement the org.springframework.boot.ExitCodeGenerator
interface if they wish to return a specific exit code when SpringApplication.exit()
is called.
This exit code can then be passed to System.exit()
to return it as a status code, as shown in the following example:
@SpringBootApplication
public class MyApplication {
@Bean
public ExitCodeGenerator exitCodeGenerator() {
return () -> 42;
}
public static void main(String[] args) {
System.exit(SpringApplication.exit(SpringApplication.run(MyApplication.class, args)));
}
}
@SpringBootApplication
class MyApplication {
@Bean
fun exitCodeGenerator() = ExitCodeGenerator { 42 }
}
fun main(args: Array<String>) {
exitProcess(SpringApplication.exit(
runApplication<MyApplication>(*args)))
}
Also, the ExitCodeGenerator
interface may be implemented by exceptions.
When such an exception is encountered, Spring Boot returns the exit code provided by the implemented getExitCode()
method.
If there is more than one ExitCodeGenerator
, the first non-zero exit code that is generated is used.
To control the order in which the generators are called, additionally implement the org.springframework.core.Ordered
interface or use the org.springframework.core.annotation.Order
annotation.
1.12. Admin Features
It is possible to enable admin-related features for the application by specifying the spring.application.admin.enabled
property.
This exposes the SpringApplicationAdminMXBean
on the platform MBeanServer
.
You could use this feature to administer your Spring Boot application remotely.
This feature could also be useful for any service wrapper implementation.
If you want to know on which HTTP port the application is running, get the property with a key of local.server.port .
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1.13. Application Startup tracking
During the application startup, the SpringApplication
and the ApplicationContext
perform many tasks related to the application lifecycle,
the beans lifecycle or even processing application events.
With ApplicationStartup
, Spring Framework allows you to track the application startup sequence with StartupStep
objects.
This data can be collected for profiling purposes, or just to have a better understanding of an application startup process.
You can choose an ApplicationStartup
implementation when setting up the SpringApplication
instance.
For example, to use the BufferingApplicationStartup
, you could write:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(MyApplication.class);
application.setApplicationStartup(new BufferingApplicationStartup(2048));
application.run(args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args) {
applicationStartup = BufferingApplicationStartup(2048)
}
}
The first available implementation, FlightRecorderApplicationStartup
is provided by Spring Framework.
It adds Spring-specific startup events to a Java Flight Recorder session and is meant for profiling applications and correlating their Spring context lifecycle with JVM events (such as allocations, GCs, class loading…).
Once configured, you can record data by running the application with the Flight Recorder enabled:
$ java -XX:StartFlightRecording:filename=recording.jfr,duration=10s -jar demo.jar
Spring Boot ships with the BufferingApplicationStartup
variant; this implementation is meant for buffering the startup steps and draining them into an external metrics system.
Applications can ask for the bean of type BufferingApplicationStartup
in any component.
Spring Boot can also be configured to expose a startup
endpoint that provides this information as a JSON document.
2. Externalized Configuration
Spring Boot lets you externalize your configuration so that you can work with the same application code in different environments. You can use a variety of external configuration sources including Java properties files, YAML files, environment variables, and command-line arguments.
Property values can be injected directly into your beans by using the @Value
annotation, accessed through Spring’s Environment
abstraction, or be bound to structured objects through @ConfigurationProperties
.
Spring Boot uses a very particular PropertySource
order that is designed to allow sensible overriding of values.
Later property sources can override the values defined in earlier ones.
Sources are considered in the following order:
-
Default properties (specified by setting
SpringApplication.setDefaultProperties
). -
@PropertySource
annotations on your@Configuration
classes. Please note that such property sources are not added to theEnvironment
until the application context is being refreshed. This is too late to configure certain properties such aslogging.*
andspring.main.*
which are read before refresh begins. -
Config data (such as
application.properties
files). -
A
RandomValuePropertySource
that has properties only inrandom.*
. -
OS environment variables.
-
Java System properties (
System.getProperties()
). -
JNDI attributes from
java:comp/env
. -
ServletContext
init parameters. -
ServletConfig
init parameters. -
Properties from
SPRING_APPLICATION_JSON
(inline JSON embedded in an environment variable or system property). -
Command line arguments.
-
properties
attribute on your tests. Available on@SpringBootTest
and the test annotations for testing a particular slice of your application. -
@TestPropertySource
annotations on your tests. -
Devtools global settings properties in the
$HOME/.config/spring-boot
directory when devtools is active.
Config data files are considered in the following order:
-
Application properties packaged inside your jar (
application.properties
and YAML variants). -
Profile-specific application properties packaged inside your jar (
application-{profile}.properties
and YAML variants). -
Application properties outside of your packaged jar (
application.properties
and YAML variants). -
Profile-specific application properties outside of your packaged jar (
application-{profile}.properties
and YAML variants).
It is recommended to stick with one format for your entire application.
If you have configuration files with both .properties and .yml format in the same location, .properties takes precedence.
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To provide a concrete example, suppose you develop a @Component
that uses a name
property, as shown in the following example:
@Component
public class MyBean {
@Value("${name}")
private String name;
// ...
}
@Component
class MyBean {
@Value("\${name}")
private val name: String? = null
// ...
}
On your application classpath (for example, inside your jar) you can have an application.properties
file that provides a sensible default property value for name
.
When running in a new environment, an application.properties
file can be provided outside of your jar that overrides the name
.
For one-off testing, you can launch with a specific command line switch (for example, java -jar app.jar --name="Spring"
).
The env and configprops endpoints can be useful in determining why a property has a particular value.
You can use these two endpoints to diagnose unexpected property values.
See the "Production ready features" section for details.
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2.1. Accessing Command Line Properties
By default, SpringApplication
converts any command line option arguments (that is, arguments starting with --
, such as --server.port=9000
) to a property
and adds them to the Spring Environment
.
As mentioned previously, command line properties always take precedence over file-based property sources.
If you do not want command line properties to be added to the Environment
, you can disable them by using SpringApplication.setAddCommandLineProperties(false)
.
2.2. JSON Application Properties
Environment variables and system properties often have restrictions that mean some property names cannot be used. To help with this, Spring Boot allows you to encode a block of properties into a single JSON structure.
When your application starts, any spring.application.json
or SPRING_APPLICATION_JSON
properties will be parsed and added to the Environment
.
For example, the SPRING_APPLICATION_JSON
property can be supplied on the command line in a UN*X shell as an environment variable:
$ SPRING_APPLICATION_JSON='{"my":{"name":"test"}}' java -jar myapp.jar
In the preceding example, you end up with my.name=test
in the Spring Environment
.
The same JSON can also be provided as a system property:
$ java -Dspring.application.json='{"my":{"name":"test"}}' -jar myapp.jar
Or you could supply the JSON by using a command line argument:
$ java -jar myapp.jar --spring.application.json='{"my":{"name":"test"}}'
If you are deploying to a classic Application Server, you could also use a JNDI variable named java:comp/env/spring.application.json
.
Although null values from the JSON will be added to the resulting property source, the PropertySourcesPropertyResolver treats null properties as missing values.
This means that the JSON cannot override properties from lower order property sources with a null value.
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2.3. External Application Properties
Spring Boot will automatically find and load application.properties
and application.yaml
files from the following locations when your application starts:
-
From the classpath
-
The classpath root
-
The classpath
/config
package
-
-
From the current directory
-
The current directory
-
The
config/
subdirectory in the current directory -
Immediate child directories of the
config/
subdirectory
-
The list is ordered by precedence (with values from lower items overriding earlier ones).
Documents from the loaded files are added as PropertySources
to the Spring Environment
.
If you do not like application
as the configuration file name, you can switch to another file name by specifying a spring.config.name
environment property.
For example, to look for myproject.properties
and myproject.yaml
files you can run your application as follows:
$ java -jar myproject.jar --spring.config.name=myproject
You can also refer to an explicit location by using the spring.config.location
environment property.
This property accepts a comma-separated list of one or more locations to check.
The following example shows how to specify two distinct files:
$ java -jar myproject.jar --spring.config.location=\
optional:classpath:/default.properties,\
optional:classpath:/override.properties
Use the prefix optional: if the locations are optional and you do not mind if they do not exist.
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spring.config.name , spring.config.location , and spring.config.additional-location are used very early to determine which files have to be loaded.
They must be defined as an environment property (typically an OS environment variable, a system property, or a command-line argument).
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If spring.config.location
contains directories (as opposed to files), they should end in /
.
At runtime they will be appended with the names generated from spring.config.name
before being loaded.
Files specified in spring.config.location
are imported directly.
Both directory and file location values are also expanded to check for profile-specific files.
For example, if you have a spring.config.location of classpath:myconfig.properties , you will also find appropriate classpath:myconfig-<profile>.properties files are loaded.
|
In most situations, each spring.config.location
item you add will reference a single file or directory.
Locations are processed in the order that they are defined and later ones can override the values of earlier ones.
If you have a complex location setup, and you use profile-specific configuration files, you may need to provide further hints so that Spring Boot knows how they should be grouped.
A location group is a collection of locations that are all considered at the same level.
For example, you might want to group all classpath locations, then all external locations.
Items within a location group should be separated with ;
.
See the example in the “Profile Specific Files” section for more details.
Locations configured by using spring.config.location
replace the default locations.
For example, if spring.config.location
is configured with the value optional:classpath:/custom-config/,optional:file:./custom-config/
, the complete set of locations considered is:
-
optional:classpath:custom-config/
-
optional:file:./custom-config/
If you prefer to add additional locations, rather than replacing them, you can use spring.config.additional-location
.
Properties loaded from additional locations can override those in the default locations.
For example, if spring.config.additional-location
is configured with the value optional:classpath:/custom-config/,optional:file:./custom-config/
, the complete set of locations considered is:
-
optional:classpath:/;optional:classpath:/config/
-
optional:file:./;optional:file:./config/;optional:file:./config/*/
-
optional:classpath:custom-config/
-
optional:file:./custom-config/
This search ordering lets you specify default values in one configuration file and then selectively override those values in another.
You can provide default values for your application in application.properties
(or whatever other basename you choose with spring.config.name
) in one of the default locations.
These default values can then be overridden at runtime with a different file located in one of the custom locations.
If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (for example, SPRING_CONFIG_NAME instead of spring.config.name ).
See Binding From Environment Variables for details.
|
If your application runs in a servlet container or application server, then JNDI properties (in java:comp/env ) or servlet context initialization parameters can be used instead of, or as well as, environment variables or system properties.
|
2.3.1. Optional Locations
By default, when a specified config data location does not exist, Spring Boot will throw a ConfigDataLocationNotFoundException
and your application will not start.
If you want to specify a location, but you do not mind if it does not always exist, you can use the optional:
prefix.
You can use this prefix with the spring.config.location
and spring.config.additional-location
properties, as well as with spring.config.import
declarations.
For example, a spring.config.import
value of optional:file:./myconfig.properties
allows your application to start, even if the myconfig.properties
file is missing.
If you want to ignore all ConfigDataLocationNotFoundExceptions
and always continue to start your application, you can use the spring.config.on-not-found
property.
Set the value to ignore
using SpringApplication.setDefaultProperties(…)
or with a system/environment variable.
2.3.2. Wildcard Locations
If a config file location includes the *
character for the last path segment, it is considered a wildcard location.
Wildcards are expanded when the config is loaded so that immediate subdirectories are also checked.
Wildcard locations are particularly useful in an environment such as Kubernetes when there are multiple sources of config properties.
For example, if you have some Redis configuration and some MySQL configuration, you might want to keep those two pieces of configuration separate, while requiring that both those are present in an application.properties
file.
This might result in two separate application.properties
files mounted at different locations such as /config/redis/application.properties
and /config/mysql/application.properties
.
In such a case, having a wildcard location of config/*/
, will result in both files being processed.
By default, Spring Boot includes config/*/
in the default search locations.
It means that all subdirectories of the /config
directory outside of your jar will be searched.
You can use wildcard locations yourself with the spring.config.location
and spring.config.additional-location
properties.
A wildcard location must contain only one * and end with */ for search locations that are directories or */<filename> for search locations that are files.
Locations with wildcards are sorted alphabetically based on the absolute path of the file names.
|
Wildcard locations only work with external directories.
You cannot use a wildcard in a classpath: location.
|
2.3.3. Profile Specific Files
As well as application
property files, Spring Boot will also attempt to load profile-specific files using the naming convention application-{profile}
.
For example, if your application activates a profile named prod
and uses YAML files, then both application.yml
and application-prod.yml
will be considered.
Profile-specific properties are loaded from the same locations as standard application.properties
, with profile-specific files always overriding the non-specific ones.
If several profiles are specified, a last-wins strategy applies.
For example, if profiles prod,live
are specified by the spring.profiles.active
property, values in application-prod.properties
can be overridden by those in application-live.properties
.
The last-wins strategy applies at the location group level.
A For example, continuing our /cfg application-live.properties /ext application-live.properties application-prod.properties When we have a
When we have
|
The Environment
has a set of default profiles (by default, [default]
) that are used if no active profiles are set.
In other words, if no profiles are explicitly activated, then properties from application-default
are considered.
Properties files are only ever loaded once. If you have already directly imported a profile specific property files then it will not be imported a second time. |
2.3.4. Importing Additional Data
Application properties may import further config data from other locations using the spring.config.import
property.
Imports are processed as they are discovered, and are treated as additional documents inserted immediately below the one that declares the import.
For example, you might have the following in your classpath application.properties
file:
spring.application.name=myapp
spring.config.import=optional:file:./dev.properties
spring:
application:
name: "myapp"
config:
import: "optional:file:./dev.properties"
This will trigger the import of a dev.properties
file in current directory (if such a file exists).
Values from the imported dev.properties
will take precedence over the file that triggered the import.
In the above example, the dev.properties
could redefine spring.application.name
to a different value.
An import will only be imported once no matter how many times it is declared. The order an import is defined inside a single document within the properties/yaml file does not matter. For instance, the two examples below produce the same result:
spring.config.import=my.properties
my.property=value
spring:
config:
import: "my.properties"
my:
property: "value"
my.property=value
spring.config.import=my.properties
my:
property: "value"
spring:
config:
import: "my.properties"
In both of the above examples, the values from the my.properties
file will take precedence over the file that triggered its import.
Several locations can be specified under a single spring.config.import
key.
Locations will be processed in the order that they are defined, with later imports taking precedence.
When appropriate, Profile-specific variants are also considered for import.
The example above would import both my.properties as well as any my-<profile>.properties variants.
|
Spring Boot includes pluggable API that allows various different location addresses to be supported. By default you can import Java Properties, YAML and “configuration trees”. Third-party jars can offer support for additional technologies (there is no requirement for files to be local). For example, you can imagine config data being from external stores such as Consul, Apache ZooKeeper or Netflix Archaius. If you want to support your own locations, see the |
2.3.5. Importing Extensionless Files
Some cloud platforms cannot add a file extension to volume mounted files. To import these extensionless files, you need to give Spring Boot a hint so that it knows how to load them. You can do this by putting an extension hint in square brackets.
For example, suppose you have a /etc/config/myconfig
file that you wish to import as yaml.
You can import it from your application.properties
using the following:
spring.config.import=file:/etc/config/myconfig[.yaml]
spring:
config:
import: "file:/etc/config/myconfig[.yaml]"
2.3.6. Using Configuration Trees
When running applications on a cloud platform (such as Kubernetes) you often need to read config values that the platform supplies. It is not uncommon to use environment variables for such purposes, but this can have drawbacks, especially if the value is supposed to be kept secret.
As an alternative to environment variables, many cloud platforms now allow you to map configuration into mounted data volumes.
For example, Kubernetes can volume mount both ConfigMaps
and Secrets
.
There are two common volume mount patterns that can be used:
-
A single file contains a complete set of properties (usually written as YAML).
-
Multiple files are written to a directory tree, with the filename becoming the ‘key’ and the contents becoming the ‘value’.
For the first case, you can import the YAML or Properties file directly using spring.config.import
as described above.
For the second case, you need to use the configtree:
prefix so that Spring Boot knows it needs to expose all the files as properties.
As an example, let’s imagine that Kubernetes has mounted the following volume:
etc/ config/ myapp/ username password
The contents of the username
file would be a config value, and the contents of password
would be a secret.
To import these properties, you can add the following to your application.properties
or application.yaml
file:
spring.config.import=optional:configtree:/etc/config/
spring:
config:
import: "optional:configtree:/etc/config/"
You can then access or inject myapp.username
and myapp.password
properties from the Environment
in the usual way.
The folders under the config tree form the property name.
In the above example, to access the properties as username and password , you can set spring.config.import to optional:configtree:/etc/config/myapp .
|
Filenames with dot notation are also correctly mapped.
For example, in the above example, a file named myapp.username in /etc/config would result in a myapp.username property in the Environment .
|
Configuration tree values can be bound to both string String and byte[] types depending on the contents expected.
|
If you have multiple config trees to import from the same parent folder you can use a wildcard shortcut.
Any configtree:
location that ends with /*/
will import all immediate children as config trees.
For example, given the following volume:
etc/ config/ dbconfig/ db/ username password mqconfig/ mq/ username password
You can use configtree:/etc/config/*/
as the import location:
spring.config.import=optional:configtree:/etc/config/*/
spring:
config:
import: "optional:configtree:/etc/config/*/"
This will add db.username
, db.password
, mq.username
and mq.password
properties.
Directories loaded using a wildcard are sorted alphabetically. If you need a different order, then you should list each location as a separate import |
Configuration trees can also be used for Docker secrets.
When a Docker swarm service is granted access to a secret, the secret gets mounted into the container.
For example, if a secret named db.password
is mounted at location /run/secrets/
, you can make db.password
available to the Spring environment using the following:
spring.config.import=optional:configtree:/run/secrets/
spring:
config:
import: "optional:configtree:/run/secrets/"
2.3.7. Property Placeholders
The values in application.properties
and application.yml
are filtered through the existing Environment
when they are used, so you can refer back to previously defined values (for example, from System properties or environment variables).
The standard ${name}
property-placeholder syntax can be used anywhere within a value.
Property placeholders can also specify a default value using a :
to separate the default value from the property name, for example ${name:default}
.
The use of placeholders with and without defaults is shown in the following example:
app.name=MyApp
app.description=${app.name} is a Spring Boot application written by ${username:Unknown}
app:
name: "MyApp"
description: "${app.name} is a Spring Boot application written by ${username:Unknown}"
Assuming that the username
property has not been set elsewhere, app.description
will have the value MyApp is a Spring Boot application written by Unknown
.
You should always refer to property names in the placeholder using their canonical form (kebab-case using only lowercase letters).
This will allow Spring Boot to use the same logic as it does when relaxed binding For example, |
You can also use this technique to create “short” variants of existing Spring Boot properties. See the howto.html how-to for details. |
2.3.8. Working With Multi-Document Files
Spring Boot allows you to split a single physical file into multiple logical documents which are each added independently. Documents are processed in order, from top to bottom. Later documents can override the properties defined in earlier ones.
For application.yml
files, the standard YAML multi-document syntax is used.
Three consecutive hyphens represent the end of one document, and the start of the next.
For example, the following file has two logical documents:
spring:
application:
name: "MyApp"
---
spring:
application:
name: "MyCloudApp"
config:
activate:
on-cloud-platform: "kubernetes"
For application.properties
files a special #---
or !---
comment is used to mark the document splits:
spring.application.name=MyApp
#---
spring.application.name=MyCloudApp
spring.config.activate.on-cloud-platform=kubernetes
Property file separators must not have any leading whitespace and must have exactly three hyphen characters. The lines immediately before and after the separator must not be same comment prefix. |
Multi-document property files are often used in conjunction with activation properties such as spring.config.activate.on-profile .
See the next section for details.
|
Multi-document property files cannot be loaded by using the @PropertySource or @TestPropertySource annotations.
|
2.3.9. Activation Properties
It is sometimes useful to only activate a given set of properties when certain conditions are met. For example, you might have properties that are only relevant when a specific profile is active.
You can conditionally activate a properties document using spring.config.activate.*
.
The following activation properties are available:
Property | Note |
---|---|
|
A profile expression that must match for the document to be active. |
|
The |
For example, the following specifies that the second document is only active when running on Kubernetes, and only when either the “prod” or “staging” profiles are active:
myprop=always-set
#---
spring.config.activate.on-cloud-platform=kubernetes
spring.config.activate.on-profile=prod | staging
myotherprop=sometimes-set
myprop:
"always-set"
---
spring:
config:
activate:
on-cloud-platform: "kubernetes"
on-profile: "prod | staging"
myotherprop: "sometimes-set"
2.4. Encrypting Properties
Spring Boot does not provide any built in support for encrypting property values, however, it does provide the hook points necessary to modify values contained in the Spring Environment
.
The EnvironmentPostProcessor
interface allows you to manipulate the Environment
before the application starts.
See howto.html for details.
If you need a secure way to store credentials and passwords, the Spring Cloud Vault project provides support for storing externalized configuration in HashiCorp Vault.
2.5. Working With YAML
YAML is a superset of JSON and, as such, is a convenient format for specifying hierarchical configuration data.
The SpringApplication
class automatically supports YAML as an alternative to properties whenever you have the SnakeYAML library on your classpath.
If you use “Starters”, SnakeYAML is automatically provided by spring-boot-starter .
|
2.5.1. Mapping YAML to Properties
YAML documents need to be converted from their hierarchical format to a flat structure that can be used with the Spring Environment
.
For example, consider the following YAML document:
environments:
dev:
url: "https://dev.example.com"
name: "Developer Setup"
prod:
url: "https://another.example.com"
name: "My Cool App"
In order to access these properties from the Environment
, they would be flattened as follows:
environments.dev.url=https://dev.example.com
environments.dev.name=Developer Setup
environments.prod.url=https://another.example.com
environments.prod.name=My Cool App
Likewise, YAML lists also need to be flattened.
They are represented as property keys with [index]
dereferencers.
For example, consider the following YAML:
my:
servers:
- "dev.example.com"
- "another.example.com"
The preceding example would be transformed into these properties:
my.servers[0]=dev.example.com
my.servers[1]=another.example.com
Properties that use the [index] notation can be bound to Java List or Set objects using Spring Boot’s Binder class.
For more details see the “Type-safe Configuration Properties” section below.
|
YAML files cannot be loaded by using the @PropertySource or @TestPropertySource annotations.
So, in the case that you need to load values that way, you need to use a properties file.
|
2.5.2. Directly Loading YAML
Spring Framework provides two convenient classes that can be used to load YAML documents.
The YamlPropertiesFactoryBean
loads YAML as Properties
and the YamlMapFactoryBean
loads YAML as a Map
.
You can also use the YamlPropertySourceLoader
class if you want to load YAML as a Spring PropertySource
.
2.6. Configuring Random Values
The RandomValuePropertySource
is useful for injecting random values (for example, into secrets or test cases).
It can produce integers, longs, uuids, or strings, as shown in the following example:
my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.uuid=${random.uuid}
my.number-less-than-ten=${random.int(10)}
my.number-in-range=${random.int[1024,65536]}
my:
secret: "${random.value}"
number: "${random.int}"
bignumber: "${random.long}"
uuid: "${random.uuid}"
number-less-than-ten: "${random.int(10)}"
number-in-range: "${random.int[1024,65536]}"
The random.int*
syntax is OPEN value (,max) CLOSE
where the OPEN,CLOSE
are any character and value,max
are integers.
If max
is provided, then value
is the minimum value and max
is the maximum value (exclusive).
2.7. Configuring System Environment Properties
Spring Boot supports setting a prefix for environment properties.
This is useful if the system environment is shared by multiple Spring Boot applications with different configuration requirements.
The prefix for system environment properties can be set directly on SpringApplication
.
For example, if you set the prefix to input
, a property such as remote.timeout
will also be resolved as input.remote.timeout
in the system environment.
2.8. Type-safe Configuration Properties
Using the @Value("${property}")
annotation to inject configuration properties can sometimes be cumbersome, especially if you are working with multiple properties or your data is hierarchical in nature.
Spring Boot provides an alternative method of working with properties that lets strongly typed beans govern and validate the configuration of your application.
2.8.1. JavaBean Properties Binding
It is possible to bind a bean declaring standard JavaBean properties as shown in the following example:
@ConfigurationProperties("my.service")
public class MyProperties {
private boolean enabled;
private InetAddress remoteAddress;
private final Security security = new Security();
public static class Security {
private String username;
private String password;
private List<String> roles = new ArrayList<>(Collections.singleton("USER"));
}
}
@ConfigurationProperties("my.service")
class MyProperties {
var isEnabled = false
var remoteAddress: InetAddress? = null
val security = Security()
class Security {
var username: String? = null
var password: String? = null
var roles: List<String> = ArrayList(setOf("USER"))
}
}
The preceding POJO defines the following properties:
-
my.service.enabled
, with a value offalse
by default. -
my.service.remote-address
, with a type that can be coerced fromString
. -
my.service.security.username
, with a nested "security" object whose name is determined by the name of the property. In particular, the type is not used at all there and could have beenSecurityProperties
. -
my.service.security.password
. -
my.service.security.roles
, with a collection ofString
that defaults toUSER
.
The properties that map to @ConfigurationProperties classes available in Spring Boot, which are configured through properties files, YAML files, environment variables, and other mechanisms, are public API but the accessors (getters/setters) of the class itself are not meant to be used directly.
|
Such arrangement relies on a default empty constructor and getters and setters are usually mandatory, since binding is through standard Java Beans property descriptors, just like in Spring MVC. A setter may be omitted in the following cases:
Some people use Project Lombok to add getters and setters automatically. Make sure that Lombok does not generate any particular constructor for such a type, as it is used automatically by the container to instantiate the object. Finally, only standard Java Bean properties are considered and binding on static properties is not supported. |
2.8.2. Constructor Binding
The example in the previous section can be rewritten in an immutable fashion as shown in the following example:
@ConstructorBinding
@ConfigurationProperties("my.service")
public class MyProperties {
public MyProperties(boolean enabled, InetAddress remoteAddress, Security security) {
this.enabled = enabled;
this.remoteAddress = remoteAddress;
this.security = security;
}
public static class Security {
public Security(String username, String password, @DefaultValue("USER") List<String> roles) {
this.username = username;
this.password = password;
this.roles = roles;
}
}
}
@ConstructorBinding
@ConfigurationProperties("my.service")
class MyProperties(val enabled: Boolean, val remoteAddress: InetAddress,
val security: Security) {
class Security(val username: String, val password: String,
@param:DefaultValue("USER") val roles: List<String>)
}
In this setup, the @ConstructorBinding
annotation is used to indicate that constructor binding should be used.
This means that the binder will expect to find a constructor with the parameters that you wish to have bound.
If you are using Java 16 or later, constructor binding can be used with records.
In this case, unless your record has multiple constructors, there is no need to use @ConstructorBinding
.
Nested members of a @ConstructorBinding
class (such as Security
in the example above) will also be bound through their constructor.
Default values can be specified using @DefaultValue
on a constructor parameter or, when using Java 16 or later, a record component.
The conversion service will be applied to coerce the String
value to the target type of a missing property.
Referring to the previous example, if no properties are bound to Security
, the MyProperties
instance will contain a null
value for security
.
To make it contain a non-null instance of Security
even when no properties are bound to it (when using Kotlin, this will require the username
and password
parameters of Security
to be declared as nullable as they do not have default values), use an empty @DefaultValue
annotation:
public MyProperties(boolean enabled, InetAddress remoteAddress, @DefaultValue Security security) {
this.enabled = enabled;
this.remoteAddress = remoteAddress;
this.security = security;
}
class MyProperties(val enabled: Boolean, val remoteAddress: InetAddress,
@DefaultValue val security: Security) {
class Security(val username: String?, val password: String?,
@param:DefaultValue("USER") val roles: List<String>)
}
To use constructor binding the class must be enabled using @EnableConfigurationProperties or configuration property scanning.
You cannot use constructor binding with beans that are created by the regular Spring mechanisms (for example @Component beans, beans created by using @Bean methods or beans loaded by using @Import )
|
If you have more than one constructor for your class you can also use @ConstructorBinding directly on the constructor that should be bound.
|
The use of java.util.Optional with @ConfigurationProperties is not recommended as it is primarily intended for use as a return type.
As such, it is not well-suited to configuration property injection.
For consistency with properties of other types, if you do declare an Optional property and it has no value, null rather than an empty Optional will be bound.
|
2.8.3. Enabling @ConfigurationProperties-annotated Types
Spring Boot provides infrastructure to bind @ConfigurationProperties
types and register them as beans.
You can either enable configuration properties on a class-by-class basis or enable configuration property scanning that works in a similar manner to component scanning.
Sometimes, classes annotated with @ConfigurationProperties
might not be suitable for scanning, for example, if you’re developing your own auto-configuration or you want to enable them conditionally.
In these cases, specify the list of types to process using the @EnableConfigurationProperties
annotation.
This can be done on any @Configuration
class, as shown in the following example:
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(SomeProperties.class)
public class MyConfiguration {
}
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(SomeProperties::class)
class MyConfiguration
@ConfigurationProperties("some.properties")
public class SomeProperties {
}
@ConfigurationProperties("some.properties")
class SomeProperties
To use configuration property scanning, add the @ConfigurationPropertiesScan
annotation to your application.
Typically, it is added to the main application class that is annotated with @SpringBootApplication
but it can be added to any @Configuration
class.
By default, scanning will occur from the package of the class that declares the annotation.
If you want to define specific packages to scan, you can do so as shown in the following example:
@SpringBootApplication
@ConfigurationPropertiesScan({ "com.example.app", "com.example.another" })
public class MyApplication {
}
@SpringBootApplication
@ConfigurationPropertiesScan("com.example.app", "com.example.another")
class MyApplication
When the Assuming that it is in the |
We recommend that @ConfigurationProperties
only deal with the environment and, in particular, does not inject other beans from the context.
For corner cases, setter injection can be used or any of the *Aware
interfaces provided by the framework (such as EnvironmentAware
if you need access to the Environment
).
If you still want to inject other beans using the constructor, the configuration properties bean must be annotated with @Component
and use JavaBean-based property binding.
2.8.4. Using @ConfigurationProperties-annotated Types
This style of configuration works particularly well with the SpringApplication
external YAML configuration, as shown in the following example:
my:
service:
remote-address: 192.168.1.1
security:
username: "admin"
roles:
- "USER"
- "ADMIN"
To work with @ConfigurationProperties
beans, you can inject them in the same way as any other bean, as shown in the following example:
@Service
public class MyService {
private final MyProperties properties;
public MyService(MyProperties properties) {
this.properties = properties;
}
public void openConnection() {
Server server = new Server(this.properties.getRemoteAddress());
server.start();
// ...
}
// ...
}
@Service
class MyService(val properties: MyProperties) {
fun openConnection() {
val server = Server(properties.remoteAddress)
server.start()
// ...
}
// ...
}
Using @ConfigurationProperties also lets you generate metadata files that can be used by IDEs to offer auto-completion for your own keys.
See the appendix for details.
|
2.8.5. Third-party Configuration
As well as using @ConfigurationProperties
to annotate a class, you can also use it on public @Bean
methods.
Doing so can be particularly useful when you want to bind properties to third-party components that are outside of your control.
To configure a bean from the Environment
properties, add @ConfigurationProperties
to its bean registration, as shown in the following example:
@Configuration(proxyBeanMethods = false)
public class ThirdPartyConfiguration {
@Bean
@ConfigurationProperties(prefix = "another")
public AnotherComponent anotherComponent() {
return new AnotherComponent();
}
}
@Configuration(proxyBeanMethods = false)
class ThirdPartyConfiguration {
@Bean
@ConfigurationProperties(prefix = "another")
fun anotherComponent(): AnotherComponent = AnotherComponent()
}
Any JavaBean property defined with the another
prefix is mapped onto that AnotherComponent
bean in manner similar to the preceding SomeProperties
example.
2.8.6. Relaxed Binding
Spring Boot uses some relaxed rules for binding Environment
properties to @ConfigurationProperties
beans, so there does not need to be an exact match between the Environment
property name and the bean property name.
Common examples where this is useful include dash-separated environment properties (for example, context-path
binds to contextPath
), and capitalized environment properties (for example, PORT
binds to port
).
As an example, consider the following @ConfigurationProperties
class:
@ConfigurationProperties(prefix = "my.main-project.person")
public class MyPersonProperties {
private String firstName;
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
}
@ConfigurationProperties(prefix = "my.main-project.person")
class MyPersonProperties {
var firstName: String? = null
}
With the preceding code, the following properties names can all be used:
Property | Note |
---|---|
|
Kebab case, which is recommended for use in |
|
Standard camel case syntax. |
|
Underscore notation, which is an alternative format for use in |
|
Upper case format, which is recommended when using system environment variables. |
The prefix value for the annotation must be in kebab case (lowercase and separated by - , such as my.main-project.person ).
|
Property Source | Simple | List |
---|---|---|
Properties Files |
Camel case, kebab case, or underscore notation |
Standard list syntax using |
YAML Files |
Camel case, kebab case, or underscore notation |
Standard YAML list syntax or comma-separated values |
Environment Variables |
Upper case format with underscore as the delimiter (see Binding From Environment Variables). |
Numeric values surrounded by underscores (see Binding From Environment Variables) |
System properties |
Camel case, kebab case, or underscore notation |
Standard list syntax using |
We recommend that, when possible, properties are stored in lower-case kebab format, such as my.person.first-name=Rod .
|
Binding Maps
When binding to Map
properties you may need to use a special bracket notation so that the original key
value is preserved.
If the key is not surrounded by []
, any characters that are not alpha-numeric, -
or .
are removed.
For example, consider binding the following properties to a Map<String,String>
:
my.map.[/key1]=value1
my.map.[/key2]=value2
my.map./key3=value3
my:
map:
"[/key1]": "value1"
"[/key2]": "value2"
"/key3": "value3"
For YAML files, the brackets need to be surrounded by quotes for the keys to be parsed properly. |
The properties above will bind to a Map
with /key1
, /key2
and key3
as the keys in the map.
The slash has been removed from key3
because it was not surrounded by square brackets.
When binding to scalar values, keys with .
in them do not need to be surrounded by []
.
Scalar values include enums and all types in the java.lang
package except for Object
.
Binding a.b=c
to Map<String, String>
will preserve the .
in the key and return a Map with the entry {"a.b"="c"}
.
For any other types you need to use the bracket notation if your key
contains a .
.
For example, binding a.b=c
to Map<String, Object>
will return a Map with the entry {"a"={"b"="c"}}
whereas [a.b]=c
will return a Map with the entry {"a.b"="c"}
.
Binding From Environment Variables
Most operating systems impose strict rules around the names that can be used for environment variables.
For example, Linux shell variables can contain only letters (a
to z
or A
to Z
), numbers (0
to 9
) or the underscore character (_
).
By convention, Unix shell variables will also have their names in UPPERCASE.
Spring Boot’s relaxed binding rules are, as much as possible, designed to be compatible with these naming restrictions.
To convert a property name in the canonical-form to an environment variable name you can follow these rules:
-
Replace dots (
.
) with underscores (_
). -
Remove any dashes (
-
). -
Convert to uppercase.
For example, the configuration property spring.main.log-startup-info
would be an environment variable named SPRING_MAIN_LOGSTARTUPINFO
.
Environment variables can also be used when binding to object lists.
To bind to a List
, the element number should be surrounded with underscores in the variable name.
For example, the configuration property my.service[0].other
would use an environment variable named MY_SERVICE_0_OTHER
.
2.8.7. Merging Complex Types
When lists are configured in more than one place, overriding works by replacing the entire list.
For example, assume a MyPojo
object with name
and description
attributes that are null
by default.
The following example exposes a list of MyPojo
objects from MyProperties
:
@ConfigurationProperties("my")
public class MyProperties {
private final List<MyPojo> list = new ArrayList<>();
public List<MyPojo> getList() {
return this.list;
}
}
@ConfigurationProperties("my")
class MyProperties {
val list: List<MyPojo> = ArrayList()
}
Consider the following configuration:
my.list[0].name=my name
my.list[0].description=my description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another name
my:
list:
- name: "my name"
description: "my description"
---
spring:
config:
activate:
on-profile: "dev"
my:
list:
- name: "my another name"
If the dev
profile is not active, MyProperties.list
contains one MyPojo
entry, as previously defined.
If the dev
profile is enabled, however, the list
still contains only one entry (with a name of my another name
and a description of null
).
This configuration does not add a second MyPojo
instance to the list, and it does not merge the items.
When a List
is specified in multiple profiles, the one with the highest priority (and only that one) is used.
Consider the following example:
my.list[0].name=my name
my.list[0].description=my description
my.list[1].name=another name
my.list[1].description=another description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another name
my:
list:
- name: "my name"
description: "my description"
- name: "another name"
description: "another description"
---
spring:
config:
activate:
on-profile: "dev"
my:
list:
- name: "my another name"
In the preceding example, if the dev
profile is active, MyProperties.list
contains one MyPojo
entry (with a name of my another name
and a description of null
).
For YAML, both comma-separated lists and YAML lists can be used for completely overriding the contents of the list.
For Map
properties, you can bind with property values drawn from multiple sources.
However, for the same property in multiple sources, the one with the highest priority is used.
The following example exposes a Map<String, MyPojo>
from MyProperties
:
@ConfigurationProperties("my")
public class MyProperties {
private final Map<String, MyPojo> map = new LinkedHashMap<>();
public Map<String, MyPojo> getMap() {
return this.map;
}
}
@ConfigurationProperties("my")
class MyProperties {
val map: Map<String, MyPojo> = LinkedHashMap()
}
Consider the following configuration:
my.map.key1.name=my name 1
my.map.key1.description=my description 1
#---
spring.config.activate.on-profile=dev
my.map.key1.name=dev name 1
my.map.key2.name=dev name 2
my.map.key2.description=dev description 2
my:
map:
key1:
name: "my name 1"
description: "my description 1"
---
spring:
config:
activate:
on-profile: "dev"
my:
map:
key1:
name: "dev name 1"
key2:
name: "dev name 2"
description: "dev description 2"
If the dev
profile is not active, MyProperties.map
contains one entry with key key1
(with a name of my name 1
and a description of my description 1
).
If the dev
profile is enabled, however, map
contains two entries with keys key1
(with a name of dev name 1
and a description of my description 1
) and key2
(with a name of dev name 2
and a description of dev description 2
).
The preceding merging rules apply to properties from all property sources, and not just files. |
2.8.8. Properties Conversion
Spring Boot attempts to coerce the external application properties to the right type when it binds to the @ConfigurationProperties
beans.
If you need custom type conversion, you can provide a ConversionService
bean (with a bean named conversionService
) or custom property editors (through a CustomEditorConfigurer
bean) or custom Converters
(with bean definitions annotated as @ConfigurationPropertiesBinding
).
As this bean is requested very early during the application lifecycle, make sure to limit the dependencies that your ConversionService is using.
Typically, any dependency that you require may not be fully initialized at creation time.
You may want to rename your custom ConversionService if it is not required for configuration keys coercion and only rely on custom converters qualified with @ConfigurationPropertiesBinding .
|
Converting Durations
Spring Boot has dedicated support for expressing durations.
If you expose a java.time.Duration
property, the following formats in application properties are available:
-
A regular
long
representation (using milliseconds as the default unit unless a@DurationUnit
has been specified) -
The standard ISO-8601 format used by
java.time.Duration
-
A more readable format where the value and the unit are coupled (
10s
means 10 seconds)
Consider the following example:
@ConfigurationProperties("my")
public class MyProperties {
@DurationUnit(ChronoUnit.SECONDS)
private Duration sessionTimeout = Duration.ofSeconds(30);
private Duration readTimeout = Duration.ofMillis(1000);
}
@ConfigurationProperties("my")
class MyProperties {
@DurationUnit(ChronoUnit.SECONDS)
var sessionTimeout = Duration.ofSeconds(30)
var readTimeout = Duration.ofMillis(1000)
}
To specify a session timeout of 30 seconds, 30
, PT30S
and 30s
are all equivalent.
A read timeout of 500ms can be specified in any of the following form: 500
, PT0.5S
and 500ms
.
You can also use any of the supported units. These are:
-
ns
for nanoseconds -
us
for microseconds -
ms
for milliseconds -
s
for seconds -
m
for minutes -
h
for hours -
d
for days
The default unit is milliseconds and can be overridden using @DurationUnit
as illustrated in the sample above.
If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:
@ConfigurationProperties("my")
@ConstructorBinding
public class MyProperties {
public MyProperties(@DurationUnit(ChronoUnit.SECONDS) @DefaultValue("30s") Duration sessionTimeout,
@DefaultValue("1000ms") Duration readTimeout) {
this.sessionTimeout = sessionTimeout;
this.readTimeout = readTimeout;
}
}
@ConfigurationProperties("my")
@ConstructorBinding
class MyProperties(@param:DurationUnit(ChronoUnit.SECONDS) @param:DefaultValue("30s") val sessionTimeout: Duration,
@param:DefaultValue("1000ms") val readTimeout: Duration)
If you are upgrading a Long property, make sure to define the unit (using @DurationUnit ) if it is not milliseconds.
Doing so gives a transparent upgrade path while supporting a much richer format.
|
Converting Periods
In addition to durations, Spring Boot can also work with java.time.Period
type.
The following formats can be used in application properties:
-
An regular
int
representation (using days as the default unit unless a@PeriodUnit
has been specified) -
The standard ISO-8601 format used by
java.time.Period
-
A simpler format where the value and the unit pairs are coupled (
1y3d
means 1 year and 3 days)
The following units are supported with the simple format:
-
y
for years -
m
for months -
w
for weeks -
d
for days
The java.time.Period type never actually stores the number of weeks, it is a shortcut that means “7 days”.
|
Converting Data Sizes
Spring Framework has a DataSize
value type that expresses a size in bytes.
If you expose a DataSize
property, the following formats in application properties are available:
-
A regular
long
representation (using bytes as the default unit unless a@DataSizeUnit
has been specified) -
A more readable format where the value and the unit are coupled (
10MB
means 10 megabytes)
Consider the following example:
@ConfigurationProperties("my")
public class MyProperties {
@DataSizeUnit(DataUnit.MEGABYTES)
private DataSize bufferSize = DataSize.ofMegabytes(2);
private DataSize sizeThreshold = DataSize.ofBytes(512);
}
@ConfigurationProperties("my")
class MyProperties {
@DataSizeUnit(DataUnit.MEGABYTES)
var bufferSize = DataSize.ofMegabytes(2)
var sizeThreshold = DataSize.ofBytes(512)
}
To specify a buffer size of 10 megabytes, 10
and 10MB
are equivalent.
A size threshold of 256 bytes can be specified as 256
or 256B
.
You can also use any of the supported units. These are:
-
B
for bytes -
KB
for kilobytes -
MB
for megabytes -
GB
for gigabytes -
TB
for terabytes
The default unit is bytes and can be overridden using @DataSizeUnit
as illustrated in the sample above.
If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:
@ConfigurationProperties("my")
@ConstructorBinding
public class MyProperties {
public MyProperties(@DataSizeUnit(DataUnit.MEGABYTES) @DefaultValue("2MB") DataSize bufferSize,
@DefaultValue("512B") DataSize sizeThreshold) {
this.bufferSize = bufferSize;
this.sizeThreshold = sizeThreshold;
}
}
@ConfigurationProperties("my")
@ConstructorBinding
class MyProperties(@param:DataSizeUnit(DataUnit.MEGABYTES) @param:DefaultValue("2MB") val bufferSize: DataSize,
@param:DefaultValue("512B") val sizeThreshold: DataSize)
If you are upgrading a Long property, make sure to define the unit (using @DataSizeUnit ) if it is not bytes.
Doing so gives a transparent upgrade path while supporting a much richer format.
|
2.8.9. @ConfigurationProperties Validation
Spring Boot attempts to validate @ConfigurationProperties
classes whenever they are annotated with Spring’s @Validated
annotation.
You can use JSR-303 javax.validation
constraint annotations directly on your configuration class.
To do so, ensure that a compliant JSR-303 implementation is on your classpath and then add constraint annotations to your fields, as shown in the following example:
@ConfigurationProperties("my.service")
@Validated
public class MyProperties {
@NotNull
private InetAddress remoteAddress;
}
@ConfigurationProperties("my.service")
@Validated
class MyProperties {
var remoteAddress: @NotNull InetAddress? = null
}
You can also trigger validation by annotating the @Bean method that creates the configuration properties with @Validated .
|
To ensure that validation is always triggered for nested properties, even when no properties are found, the associated field must be annotated with @Valid
.
The following example builds on the preceding MyProperties
example:
@ConfigurationProperties("my.service")
@Validated
public class MyProperties {
@NotNull
private InetAddress remoteAddress;
@Valid
private final Security security = new Security();
public static class Security {
@NotEmpty
private String username;
}
}
@ConfigurationProperties("my.service")
@Validated
class MyProperties {
var remoteAddress: @NotNull InetAddress? = null
@Valid
val security = Security()
class Security {
@NotEmpty
var username: String? = null
}
}
You can also add a custom Spring Validator
by creating a bean definition called configurationPropertiesValidator
.
The @Bean
method should be declared static
.
The configuration properties validator is created very early in the application’s lifecycle, and declaring the @Bean
method as static lets the bean be created without having to instantiate the @Configuration
class.
Doing so avoids any problems that may be caused by early instantiation.
The spring-boot-actuator module includes an endpoint that exposes all @ConfigurationProperties beans.
Point your web browser to /actuator/configprops or use the equivalent JMX endpoint.
See the "Production ready features" section for details.
|
2.8.10. @ConfigurationProperties vs. @Value
The @Value
annotation is a core container feature, and it does not provide the same features as type-safe configuration properties.
The following table summarizes the features that are supported by @ConfigurationProperties
and @Value
:
Feature | @ConfigurationProperties |
@Value |
---|---|---|
Yes |
Limited (see note below) |
|
Yes |
No |
|
|
No |
Yes |
If you do want to use For example, |
If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with @ConfigurationProperties
.
Doing so will provide you with structured, type-safe object that you can inject into your own beans.
SpEL
expressions from application property files are not processed at time of parsing these files and populating the environment.
However, it is possible to write a SpEL
expression in @Value
.
If the value of a property from an application property file is a SpEL
expression, it will be evaluated when consumed through @Value
.
3. Profiles
Spring Profiles provide a way to segregate parts of your application configuration and make it be available only in certain environments.
Any @Component
, @Configuration
or @ConfigurationProperties
can be marked with @Profile
to limit when it is loaded, as shown in the following example:
@Configuration(proxyBeanMethods = false)
@Profile("production")
public class ProductionConfiguration {
// ...
}
@Configuration(proxyBeanMethods = false)
@Profile("production")
class ProductionConfiguration {
// ...
}
If @ConfigurationProperties beans are registered through @EnableConfigurationProperties instead of automatic scanning, the @Profile annotation needs to be specified on the @Configuration class that has the @EnableConfigurationProperties annotation.
In the case where @ConfigurationProperties are scanned, @Profile can be specified on the @ConfigurationProperties class itself.
|
You can use a spring.profiles.active
Environment
property to specify which profiles are active.
You can specify the property in any of the ways described earlier in this chapter.
For example, you could include it in your application.properties
, as shown in the following example:
spring.profiles.active=dev,hsqldb
spring:
profiles:
active: "dev,hsqldb"
You could also specify it on the command line by using the following switch: --spring.profiles.active=dev,hsqldb
.
If no profile is active, a default profile is enabled.
The name of the default profile is default
and it can be tuned using the spring.profiles.default
Environment
property, as shown in the following example:
spring.profiles.default=none
spring:
profiles:
default: "none"
spring.profiles.active
and spring.profiles.default
can only be used in non-profile specific documents.
This means they cannot be included in profile specific files or documents activated by spring.config.activate.on-profile
.
For example, the second document configuration is invalid:
# this document is valid
spring.profiles.active=prod
#---
# this document is invalid
spring.config.activate.on-profile=prod
spring.profiles.active=metrics
# this document is valid
spring:
profiles:
active: "prod"
---
# this document is invalid
spring:
config:
activate:
on-profile: "prod"
profiles:
active: "metrics"
3.1. Adding Active Profiles
The spring.profiles.active
property follows the same ordering rules as other properties: The highest PropertySource
wins.
This means that you can specify active profiles in application.properties
and then replace them by using the command line switch.
Sometimes, it is useful to have properties that add to the active profiles rather than replace them.
The spring.profiles.include
property can be used to add active profiles on top of those activated by the spring.profiles.active
property.
The SpringApplication
entry point also has a Java API for setting additional profiles.
See the setAdditionalProfiles()
method in SpringApplication.
For example, when an application with the following properties is run, the common and local profiles will be activated even when it runs using the --spring.profiles.active switch:
spring.profiles.include[0]=common
spring.profiles.include[1]=local
spring:
profiles:
include:
- "common"
- "local"
Similar to spring.profiles.active , spring.profiles.include can only be used in non-profile specific documents.
This means it cannot be included in profile specific files or documents activated by spring.config.activate.on-profile .
|
Profile groups, which are described in the next section can also be used to add active profiles if a given profile is active.
3.2. Profile Groups
Occasionally the profiles that you define and use in your application are too fine-grained and become cumbersome to use.
For example, you might have proddb
and prodmq
profiles that you use to enable database and messaging features independently.
To help with this, Spring Boot lets you define profile groups. A profile group allows you to define a logical name for a related group of profiles.
For example, we can create a production
group that consists of our proddb
and prodmq
profiles.
spring.profiles.group.production[0]=proddb
spring.profiles.group.production[1]=prodmq
spring:
profiles:
group:
production:
- "proddb"
- "prodmq"
Our application can now be started using --spring.profiles.active=production
to active the production
, proddb
and prodmq
profiles in one hit.
3.3. Programmatically Setting Profiles
You can programmatically set active profiles by calling SpringApplication.setAdditionalProfiles(…)
before your application runs.
It is also possible to activate profiles by using Spring’s ConfigurableEnvironment
interface.
3.4. Profile-specific Configuration Files
Profile-specific variants of both application.properties
(or application.yml
) and files referenced through @ConfigurationProperties
are considered as files and loaded.
See "Profile Specific Files" for details.
4. Logging
Spring Boot uses Commons Logging for all internal logging but leaves the underlying log implementation open. Default configurations are provided for Java Util Logging, Log4J2, and Logback. In each case, loggers are pre-configured to use console output with optional file output also available.
By default, if you use the “Starters”, Logback is used for logging. Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J, or SLF4J all work correctly.
There are a lot of logging frameworks available for Java. Do not worry if the above list seems confusing. Generally, you do not need to change your logging dependencies and the Spring Boot defaults work just fine. |
When you deploy your application to a servlet container or application server, logging performed with the Java Util Logging API is not routed into your application’s logs. This prevents logging performed by the container or other applications that have been deployed to it from appearing in your application’s logs. |
4.1. Log Format
The default log output from Spring Boot resembles the following example:
2023-02-23 08:16:19.375 INFO 16560 --- [ main] o.s.b.d.f.s.MyApplication : Starting MyApplication using Java 1.8.0_362 on myhost with PID 16560 (/opt/apps/myapp.jar started by myuser in /opt/apps/) 2023-02-23 08:16:19.381 INFO 16560 --- [ main] o.s.b.d.f.s.MyApplication : No active profile set, falling back to 1 default profile: "default" 2023-02-23 08:16:20.417 INFO 16560 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http) 2023-02-23 08:16:20.431 INFO 16560 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2023-02-23 08:16:20.431 INFO 16560 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.71] 2023-02-23 08:16:20.505 INFO 16560 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2023-02-23 08:16:20.505 INFO 16560 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1012 ms 2023-02-23 08:16:20.902 INFO 16560 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '' 2023-02-23 08:16:20.913 INFO 16560 --- [ main] o.s.b.d.f.s.MyApplication : Started MyApplication in 2.077 seconds (JVM running for 2.5)
The following items are output:
-
Date and Time: Millisecond precision and easily sortable.
-
Log Level:
ERROR
,WARN
,INFO
,DEBUG
, orTRACE
. -
Process ID.
-
A
---
separator to distinguish the start of actual log messages. -
Thread name: Enclosed in square brackets (may be truncated for console output).
-
Logger name: This is usually the source class name (often abbreviated).
-
The log message.
Logback does not have a FATAL level.
It is mapped to ERROR .
|
4.2. Console Output
The default log configuration echoes messages to the console as they are written.
By default, ERROR
-level, WARN
-level, and INFO
-level messages are logged.
You can also enable a “debug” mode by starting your application with a --debug
flag.
$ java -jar myapp.jar --debug
You can also specify debug=true in your application.properties .
|
When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate, and Spring Boot) are configured to output more information.
Enabling the debug mode does not configure your application to log all messages with DEBUG
level.
Alternatively, you can enable a “trace” mode by starting your application with a --trace
flag (or trace=true
in your application.properties
).
Doing so enables trace logging for a selection of core loggers (embedded container, Hibernate schema generation, and the whole Spring portfolio).
4.2.1. Color-coded Output
If your terminal supports ANSI, color output is used to aid readability.
You can set spring.output.ansi.enabled
to a supported value to override the auto-detection.
Color coding is configured by using the %clr
conversion word.
In its simplest form, the converter colors the output according to the log level, as shown in the following example:
%clr(%5p)
The following table describes the mapping of log levels to colors:
Level | Color |
---|---|
|
Red |
|
Red |
|
Yellow |
|
Green |
|
Green |
|
Green |
Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion. For example, to make the text yellow, use the following setting:
%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}
The following colors and styles are supported:
-
blue
-
cyan
-
faint
-
green
-
magenta
-
red
-
yellow
4.3. File Output
By default, Spring Boot logs only to the console and does not write log files.
If you want to write log files in addition to the console output, you need to set a logging.file.name
or logging.file.path
property (for example, in your application.properties
).
The following table shows how the logging.*
properties can be used together:
logging.file.name |
logging.file.path |
Example | Description |
---|---|---|---|
(none) |
(none) |
Console only logging. |
|
Specific file |
(none) |
|
Writes to the specified log file. Names can be an exact location or relative to the current directory. |
(none) |
Specific directory |
|
Writes |
Log files rotate when they reach 10 MB and, as with console output, ERROR
-level, WARN
-level, and INFO
-level messages are logged by default.
Logging properties are independent of the actual logging infrastructure.
As a result, specific configuration keys (such as logback.configurationFile for Logback) are not managed by spring Boot.
|
4.4. File Rotation
If you are using the Logback, it is possible to fine-tune log rotation settings using your application.properties
or application.yaml
file.
For all other logging system, you will need to configure rotation settings directly yourself (for example, if you use Log4J2 then you could add a log4j2.xml
or log4j2-spring.xml
file).
The following rotation policy properties are supported:
Name | Description |
---|---|
|
The filename pattern used to create log archives. |
|
If log archive cleanup should occur when the application starts. |
|
The maximum size of log file before it is archived. |
|
The maximum amount of size log archives can take before being deleted. |
|
The maximum number of archive log files to keep (defaults to 7). |
4.5. Log Levels
All the supported logging systems can have the logger levels set in the Spring Environment
(for example, in application.properties
) by using logging.level.<logger-name>=<level>
where level
is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, or OFF.
The root
logger can be configured by using logging.level.root
.
The following example shows potential logging settings in application.properties
:
logging.level.root=warn
logging.level.org.springframework.web=debug
logging.level.org.hibernate=error
logging:
level:
root: "warn"
org.springframework.web: "debug"
org.hibernate: "error"
It is also possible to set logging levels using environment variables.
For example, LOGGING_LEVEL_ORG_SPRINGFRAMEWORK_WEB=DEBUG
will set org.springframework.web
to DEBUG
.
The above approach will only work for package level logging.
Since relaxed binding always converts environment variables to lowercase, it is not possible to configure logging for an individual class in this way.
If you need to configure logging for a class, you can use the SPRING_APPLICATION_JSON variable.
|
4.6. Log Groups
It is often useful to be able to group related loggers together so that they can all be configured at the same time. For example, you might commonly change the logging levels for all Tomcat related loggers, but you can not easily remember top level packages.
To help with this, Spring Boot allows you to define logging groups in your Spring Environment
.
For example, here is how you could define a “tomcat” group by adding it to your application.properties
:
logging.group.tomcat=org.apache.catalina,org.apache.coyote,org.apache.tomcat
logging:
group:
tomcat: "org.apache.catalina,org.apache.coyote,org.apache.tomcat"
Once defined, you can change the level for all the loggers in the group with a single line:
logging.level.tomcat=trace
logging:
level:
tomcat: "trace"
Spring Boot includes the following pre-defined logging groups that can be used out-of-the-box:
Name | Loggers |
---|---|
web |
|
sql |
|
4.7. Using a Log Shutdown Hook
In order to release logging resources when your application terminates, a shutdown hook that will trigger log system cleanup when the JVM exits is provided.
This shutdown hook is registered automatically unless your application is deployed as a war file.
If your application has complex context hierarchies the shutdown hook may not meet your needs.
If it does not, disable the shutdown hook and investigate the options provided directly by the underlying logging system.
For example, Logback offers context selectors which allow each Logger to be created in its own context.
You can use the logging.register-shutdown-hook
property to disable the shutdown hook.
Setting it to false
will disable the registration.
You can set the property in your application.properties
or application.yaml
file:
logging.register-shutdown-hook=false
logging:
register-shutdown-hook: false
4.8. Custom Log Configuration
The various logging systems can be activated by including the appropriate libraries on the classpath and can be further customized by providing a suitable configuration file in the root of the classpath or in a location specified by the following Spring Environment
property: logging.config
.
You can force Spring Boot to use a particular logging system by using the org.springframework.boot.logging.LoggingSystem
system property.
The value should be the fully qualified class name of a LoggingSystem
implementation.
You can also disable Spring Boot’s logging configuration entirely by using a value of none
.
Since logging is initialized before the ApplicationContext is created, it is not possible to control logging from @PropertySources in Spring @Configuration files.
The only way to change the logging system or disable it entirely is through System properties.
|
Depending on your logging system, the following files are loaded:
Logging System | Customization |
---|---|
Logback |
|
Log4j2 |
|
JDK (Java Util Logging) |
|
When possible, we recommend that you use the -spring variants for your logging configuration (for example, logback-spring.xml rather than logback.xml ).
If you use standard configuration locations, Spring cannot completely control log initialization.
|
There are known classloading issues with Java Util Logging that cause problems when running from an 'executable jar'. We recommend that you avoid it when running from an 'executable jar' if at all possible. |
To help with the customization, some other properties are transferred from the Spring Environment
to System properties, as described in the following table:
Spring Environment | System Property | Comments |
---|---|---|
|
|
The conversion word used when logging exceptions. |
|
|
If defined, it is used in the default log configuration. |
|
|
If defined, it is used in the default log configuration. |
|
|
The log pattern to use on the console (stdout). |
|
|
Appender pattern for log date format. |
|
|
The charset to use for console logging. |
|
|
The log pattern to use in a file (if |
|
|
The charset to use for file logging (if |
|
|
The format to use when rendering the log level (default |
|
|
The current process ID (discovered if possible and when not already defined as an OS environment variable). |
If you use Logback, the following properties are also transferred:
Spring Environment | System Property | Comments |
---|---|---|
|
|
Pattern for rolled-over log file names (default |
|
|
Whether to clean the archive log files on startup. |
|
|
Maximum log file size. |
|
|
Total size of log backups to be kept. |
|
|
Maximum number of archive log files to keep. |
All the supported logging systems can consult System properties when parsing their configuration files.
See the default configurations in spring-boot.jar
for examples:
If you want to use a placeholder in a logging property, you should use Spring Boot’s syntax and not the syntax of the underlying framework.
Notably, if you use Logback, you should use |
You can add MDC and other ad-hoc content to log lines by overriding only the 2019-08-30 12:30:04.031 user:someone INFO 22174 --- [ nio-8080-exec-0] demo.Controller Handling authenticated request |
4.9. Logback Extensions
Spring Boot includes a number of extensions to Logback that can help with advanced configuration.
You can use these extensions in your logback-spring.xml
configuration file.
Because the standard logback.xml configuration file is loaded too early, you cannot use extensions in it.
You need to either use logback-spring.xml or define a logging.config property.
|
The extensions cannot be used with Logback’s configuration scanning. If you attempt to do so, making changes to the configuration file results in an error similar to one of the following being logged: |
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]] ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]
4.9.1. Profile-specific Configuration
The <springProfile>
tag lets you optionally include or exclude sections of configuration based on the active Spring profiles.
Profile sections are supported anywhere within the <configuration>
element.
Use the name
attribute to specify which profile accepts the configuration.
The <springProfile>
tag can contain a profile name (for example staging
) or a profile expression.
A profile expression allows for more complicated profile logic to be expressed, for example production & (eu-central | eu-west)
.
Check the reference guide for more details.
The following listing shows three sample profiles:
<springProfile name="staging">
<!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>
<springProfile name="dev | staging">
<!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>
<springProfile name="!production">
<!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>
4.9.2. Environment Properties
The <springProperty>
tag lets you expose properties from the Spring Environment
for use within Logback.
Doing so can be useful if you want to access values from your application.properties
file in your Logback configuration.
The tag works in a similar way to Logback’s standard <property>
tag.
However, rather than specifying a direct value
, you specify the source
of the property (from the Environment
).
If you need to store the property somewhere other than in local
scope, you can use the scope
attribute.
If you need a fallback value (in case the property is not set in the Environment
), you can use the defaultValue
attribute.
The following example shows how to expose properties for use within Logback:
<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
<remoteHost>${fluentHost}</remoteHost>
...
</appender>
The source must be specified in kebab case (such as my.property-name ).
However, properties can be added to the Environment by using the relaxed rules.
|
5. Internationalization
Spring Boot supports localized messages so that your application can cater to users of different language preferences.
By default, Spring Boot looks for the presence of a messages
resource bundle at the root of the classpath.
The auto-configuration applies when the default properties file for the configured resource bundle is available (messages.properties by default).
If your resource bundle contains only language-specific properties files, you are required to add the default.
If no properties file is found that matches any of the configured base names, there will be no auto-configured MessageSource .
|
The basename of the resource bundle as well as several other attributes can be configured using the spring.messages
namespace, as shown in the following example:
spring.messages.basename=messages,config.i18n.messages
spring.messages.fallback-to-system-locale=false
spring:
messages:
basename: "messages,config.i18n.messages"
fallback-to-system-locale: false
spring.messages.basename supports comma-separated list of locations, either a package qualifier or a resource resolved from the classpath root.
|
See MessageSourceProperties
for more supported options.
6. JSON
Spring Boot provides integration with three JSON mapping libraries:
-
Gson
-
Jackson
-
JSON-B
Jackson is the preferred and default library.
6.1. Jackson
Auto-configuration for Jackson is provided and Jackson is part of spring-boot-starter-json
.
When Jackson is on the classpath an ObjectMapper
bean is automatically configured.
Several configuration properties are provided for customizing the configuration of the ObjectMapper
.
6.1.1. Custom Serializers and Deserializers
If you use Jackson to serialize and deserialize JSON data, you might want to write your own JsonSerializer
and JsonDeserializer
classes.
Custom serializers are usually registered with Jackson through a module, but Spring Boot provides an alternative @JsonComponent
annotation that makes it easier to directly register Spring Beans.
You can use the @JsonComponent
annotation directly on JsonSerializer
, JsonDeserializer
or KeyDeserializer
implementations.
You can also use it on classes that contain serializers/deserializers as inner classes, as shown in the following example:
@JsonComponent
public class MyJsonComponent {
public static class Serializer extends JsonSerializer<MyObject> {
@Override
public void serialize(MyObject value, JsonGenerator jgen, SerializerProvider serializers) throws IOException {
jgen.writeStartObject();
jgen.writeStringField("name", value.getName());
jgen.writeNumberField("age", value.getAge());
jgen.writeEndObject();
}
}
public static class Deserializer extends JsonDeserializer<MyObject> {
@Override
public MyObject deserialize(JsonParser jsonParser, DeserializationContext ctxt) throws IOException {
ObjectCodec codec = jsonParser.getCodec();
JsonNode tree = codec.readTree(jsonParser);
String name = tree.get("name").textValue();
int age = tree.get("age").intValue();
return new MyObject(name, age);
}
}
}
@JsonComponent
class MyJsonComponent {
class Serializer : JsonSerializer<MyObject>() {
@Throws(IOException::class)
override fun serialize(value: MyObject, jgen: JsonGenerator, serializers: SerializerProvider) {
jgen.writeStartObject()
jgen.writeStringField("name", value.name)
jgen.writeNumberField("age", value.age)
jgen.writeEndObject()
}
}
class Deserializer : JsonDeserializer<MyObject>() {
@Throws(IOException::class, JsonProcessingException::class)
override fun deserialize(jsonParser: JsonParser, ctxt: DeserializationContext): MyObject {
val codec = jsonParser.codec
val tree = codec.readTree<JsonNode>(jsonParser)
val name = tree["name"].textValue()
val age = tree["age"].intValue()
return MyObject(name, age)
}
}
}
All @JsonComponent
beans in the ApplicationContext
are automatically registered with Jackson.
Because @JsonComponent
is meta-annotated with @Component
, the usual component-scanning rules apply.
Spring Boot also provides JsonObjectSerializer
and JsonObjectDeserializer
base classes that provide useful alternatives to the standard Jackson versions when serializing objects.
See JsonObjectSerializer
and JsonObjectDeserializer
in the Javadoc for details.
The example above can be rewritten to use JsonObjectSerializer
/JsonObjectDeserializer
as follows:
@JsonComponent
public class MyJsonComponent {
public static class Serializer extends JsonObjectSerializer<MyObject> {
@Override
protected void serializeObject(MyObject value, JsonGenerator jgen, SerializerProvider provider)
throws IOException {
jgen.writeStringField("name", value.getName());
jgen.writeNumberField("age", value.getAge());
}
}
public static class Deserializer extends JsonObjectDeserializer<MyObject> {
@Override
protected MyObject deserializeObject(JsonParser jsonParser, DeserializationContext context, ObjectCodec codec,
JsonNode tree) throws IOException {
String name = nullSafeValue(tree.get("name"), String.class);
int age = nullSafeValue(tree.get("age"), Integer.class);
return new MyObject(name, age);
}
}
}
`object`
@JsonComponent
class MyJsonComponent {
class Serializer : JsonObjectSerializer<MyObject>() {
@Throws(IOException::class)
override fun serializeObject(value: MyObject, jgen: JsonGenerator, provider: SerializerProvider) {
jgen.writeStringField("name", value.name)
jgen.writeNumberField("age", value.age)
}
}
class Deserializer : JsonObjectDeserializer<MyObject>() {
@Throws(IOException::class)
override fun deserializeObject(jsonParser: JsonParser, context: DeserializationContext,
codec: ObjectCodec, tree: JsonNode): MyObject {
val name = nullSafeValue(tree["name"], String::class.java)
val age = nullSafeValue(tree["age"], Int::class.java)
return MyObject(name, age)
}
}
}
6.1.2. Mixins
Jackson has support for mixins that can be used to mix additional annotations into those already declared on a target class.
Spring Boot’s Jackson auto-configuration will scan your application’s packages for classes annotated with @JsonMixin
and register them with the auto-configured ObjectMapper
.
The registration is performed by Spring Boot’s JsonMixinModule
.
7. Task Execution and Scheduling
In the absence of an Executor
bean in the context, Spring Boot auto-configures a ThreadPoolTaskExecutor
with sensible defaults that can be automatically associated to asynchronous task execution (@EnableAsync
) and Spring MVC asynchronous request processing.
If you have defined a custom The auto-configured |
The thread pool uses 8 core threads that can grow and shrink according to the load.
Those default settings can be fine-tuned using the spring.task.execution
namespace, as shown in the following example:
spring.task.execution.pool.max-size=16
spring.task.execution.pool.queue-capacity=100
spring.task.execution.pool.keep-alive=10s
spring:
task:
execution:
pool:
max-size: 16
queue-capacity: 100
keep-alive: "10s"
This changes the thread pool to use a bounded queue so that when the queue is full (100 tasks), the thread pool increases to maximum 16 threads. Shrinking of the pool is more aggressive as threads are reclaimed when they are idle for 10 seconds (rather than 60 seconds by default).
A ThreadPoolTaskScheduler
can also be auto-configured if need to be associated to scheduled task execution (using @EnableScheduling
for instance).
The thread pool uses one thread by default and its settings can be fine-tuned using the spring.task.scheduling
namespace, as shown in the following example:
spring.task.scheduling.thread-name-prefix=scheduling-
spring.task.scheduling.pool.size=2
spring:
task:
scheduling:
thread-name-prefix: "scheduling-"
pool:
size: 2
Both a TaskExecutorBuilder
bean and a TaskSchedulerBuilder
bean are made available in the context if a custom executor or scheduler needs to be created.
8. Testing
Spring Boot provides a number of utilities and annotations to help when testing your application.
Test support is provided by two modules: spring-boot-test
contains core items, and spring-boot-test-autoconfigure
supports auto-configuration for tests.
Most developers use the spring-boot-starter-test
“Starter”, which imports both Spring Boot test modules as well as JUnit Jupiter, AssertJ, Hamcrest, and a number of other useful libraries.
If you have tests that use JUnit 4, JUnit 5’s vintage engine can be used to run them.
To use the vintage engine, add a dependency on
|
hamcrest-core
is excluded in favor of org.hamcrest:hamcrest
that is part of spring-boot-starter-test
.
8.1. Test Scope Dependencies
The spring-boot-starter-test
“Starter” (in the test
scope
) contains the following provided libraries:
-
JUnit 5: The de-facto standard for unit testing Java applications.
-
Spring Test & Spring Boot Test: Utilities and integration test support for Spring Boot applications.
-
AssertJ: A fluent assertion library.
-
Hamcrest: A library of matcher objects (also known as constraints or predicates).
-
Mockito: A Java mocking framework.
-
JSONassert: An assertion library for JSON.
-
JsonPath: XPath for JSON.
We generally find these common libraries to be useful when writing tests. If these libraries do not suit your needs, you can add additional test dependencies of your own.
8.2. Testing Spring Applications
One of the major advantages of dependency injection is that it should make your code easier to unit test.
You can instantiate objects by using the new
operator without even involving Spring.
You can also use mock objects instead of real dependencies.
Often, you need to move beyond unit testing and start integration testing (with a Spring ApplicationContext
).
It is useful to be able to perform integration testing without requiring deployment of your application or needing to connect to other infrastructure.
The Spring Framework includes a dedicated test module for such integration testing.
You can declare a dependency directly to org.springframework:spring-test
or use the spring-boot-starter-test
“Starter” to pull it in transitively.
If you have not used the spring-test
module before, you should start by reading the relevant section of the Spring Framework reference documentation.
8.3. Testing Spring Boot Applications
A Spring Boot application is a Spring ApplicationContext
, so nothing very special has to be done to test it beyond what you would normally do with a vanilla Spring context.
External properties, logging, and other features of Spring Boot are installed in the context by default only if you use SpringApplication to create it.
|
Spring Boot provides a @SpringBootTest
annotation, which can be used as an alternative to the standard spring-test
@ContextConfiguration
annotation when you need Spring Boot features.
The annotation works by creating the ApplicationContext
used in your tests through SpringApplication
.
In addition to @SpringBootTest
a number of other annotations are also provided for testing more specific slices of an application.
If you are using JUnit 4, do not forget to also add @RunWith(SpringRunner.class) to your test, otherwise the annotations will be ignored.
If you are using JUnit 5, there is no need to add the equivalent @ExtendWith(SpringExtension.class) as @SpringBootTest and the other @…Test annotations are already annotated with it.
|
By default, @SpringBootTest
will not start a server.
You can use the webEnvironment
attribute of @SpringBootTest
to further refine how your tests run:
-
MOCK
(Default) : Loads a webApplicationContext
and provides a mock web environment. Embedded servers are not started when using this annotation. If a web environment is not available on your classpath, this mode transparently falls back to creating a regular non-webApplicationContext
. It can be used in conjunction with@AutoConfigureMockMvc
or@AutoConfigureWebTestClient
for mock-based testing of your web application. -
RANDOM_PORT
: Loads aWebServerApplicationContext
and provides a real web environment. Embedded servers are started and listen on a random port. -
DEFINED_PORT
: Loads aWebServerApplicationContext
and provides a real web environment. Embedded servers are started and listen on a defined port (from yourapplication.properties
) or on the default port of8080
. -
NONE
: Loads anApplicationContext
by usingSpringApplication
but does not provide any web environment (mock or otherwise).
If your test is @Transactional , it rolls back the transaction at the end of each test method by default.
However, as using this arrangement with either RANDOM_PORT or DEFINED_PORT implicitly provides a real servlet environment, the HTTP client and server run in separate threads and, thus, in separate transactions.
Any transaction initiated on the server does not roll back in this case.
|
@SpringBootTest with webEnvironment = WebEnvironment.RANDOM_PORT will also start the management server on a separate random port if your application uses a different port for the management server.
|
8.3.1. Detecting Web Application Type
If Spring MVC is available, a regular MVC-based application context is configured. If you have only Spring WebFlux, we will detect that and configure a WebFlux-based application context instead.
If both are present, Spring MVC takes precedence.
If you want to test a reactive web application in this scenario, you must set the spring.main.web-application-type
property:
@SpringBootTest(properties = "spring.main.web-application-type=reactive")
class MyWebFluxTests {
// ...
}
@SpringBootTest(properties = ["spring.main.web-application-type=reactive"])
class MyWebFluxTests {
// ...
}
8.3.2. Detecting Test Configuration
If you are familiar with the Spring Test Framework, you may be used to using @ContextConfiguration(classes=…)
in order to specify which Spring @Configuration
to load.
Alternatively, you might have often used nested @Configuration
classes within your test.
When testing Spring Boot applications, this is often not required.
Spring Boot’s @*Test
annotations search for your primary configuration automatically whenever you do not explicitly define one.
The search algorithm works up from the package that contains the test until it finds a class annotated with @SpringBootApplication
or @SpringBootConfiguration
.
As long as you structured your code in a sensible way, your main configuration is usually found.
If you use a test annotation to test a more specific slice of your application, you should avoid adding configuration settings that are specific to a particular area on the main method’s application class. The underlying component scan configuration of |
If you want to customize the primary configuration, you can use a nested @TestConfiguration
class.
Unlike a nested @Configuration
class, which would be used instead of your application’s primary configuration, a nested @TestConfiguration
class is used in addition to your application’s primary configuration.
Spring’s test framework caches application contexts between tests. Therefore, as long as your tests share the same configuration (no matter how it is discovered), the potentially time-consuming process of loading the context happens only once. |
8.3.3. Excluding Test Configuration
If your application uses component scanning (for example, if you use @SpringBootApplication
or @ComponentScan
), you may find top-level configuration classes that you created only for specific tests accidentally get picked up everywhere.
As we have seen earlier, @TestConfiguration
can be used on an inner class of a test to customize the primary configuration.
When placed on a top-level class, @TestConfiguration
indicates that classes in src/test/java
should not be picked up by scanning.
You can then import that class explicitly where it is required, as shown in the following example:
@SpringBootTest
@Import(MyTestsConfiguration.class)
class MyTests {
@Test
void exampleTest() {
// ...
}
}
@SpringBootTest
@Import(MyTestsConfiguration::class)
class MyTests {
@Test
fun exampleTest() {
// ...
}
}
If you directly use @ComponentScan (that is, not through @SpringBootApplication ) you need to register the TypeExcludeFilter with it.
See the Javadoc for details.
|
8.3.4. Using Application Arguments
If your application expects arguments, you can
have @SpringBootTest
inject them using the args
attribute.
@SpringBootTest(args = "--app.test=one")
class MyApplicationArgumentTests {
@Test
void applicationArgumentsPopulated(@Autowired ApplicationArguments args) {
assertThat(args.getOptionNames()).containsOnly("app.test");
assertThat(args.getOptionValues("app.test")).containsOnly("one");
}
}
@SpringBootTest(args = ["--app.test=one"])
class MyApplicationArgumentTests {
@Test
fun applicationArgumentsPopulated(@Autowired args: ApplicationArguments) {
assertThat(args.optionNames).containsOnly("app.test")
assertThat(args.getOptionValues("app.test")).containsOnly("one")
}
}
8.3.5. Testing With a Mock Environment
By default, @SpringBootTest
does not start the server but instead sets up a mock environment for testing web endpoints.
With Spring MVC, we can query our web endpoints using MockMvc
or WebTestClient
, as shown in the following example:
@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {
@Test
void testWithMockMvc(@Autowired MockMvc mvc) throws Exception {
mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
}
// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
@Test
void testWithWebTestClient(@Autowired WebTestClient webClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Hello World");
}
}
@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {
@Test
fun testWithMockMvc(@Autowired mvc: MockMvc) {
mvc.perform(MockMvcRequestBuilders.get("/")).andExpect(MockMvcResultMatchers.status().isOk)
.andExpect(MockMvcResultMatchers.content().string("Hello World"))
}
// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
@Test
fun testWithWebTestClient(@Autowired webClient: WebTestClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Hello World")
}
}
If you want to focus only on the web layer and not start a complete ApplicationContext , consider using @WebMvcTest instead.
|
With Spring WebFlux endpoints, you can use WebTestClient
as shown in the following example:
@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {
@Test
void exampleTest(@Autowired WebTestClient webClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Hello World");
}
}
@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {
@Test
fun exampleTest(@Autowired webClient: WebTestClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Hello World")
}
}
Testing within a mocked environment is usually faster than running with a full servlet container. However, since mocking occurs at the Spring MVC layer, code that relies on lower-level servlet container behavior cannot be directly tested with MockMvc. For example, Spring Boot’s error handling is based on the “error page” support provided by the servlet container. This means that, whilst you can test your MVC layer throws and handles exceptions as expected, you cannot directly test that a specific custom error page is rendered. If you need to test these lower-level concerns, you can start a fully running server as described in the next section. |
8.3.6. Testing With a Running Server
If you need to start a full running server, we recommend that you use random ports.
If you use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT)
, an available port is picked at random each time your test runs.
The @LocalServerPort
annotation can be used to inject the actual port used into your test.
For convenience, tests that need to make REST calls to the started server can additionally @Autowire
a WebTestClient
, which resolves relative links to the running server and comes with a dedicated API for verifying responses, as shown in the following example:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortWebTestClientTests {
@Test
void exampleTest(@Autowired WebTestClient webClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Hello World");
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortWebTestClientTests {
@Test
fun exampleTest(@Autowired webClient: WebTestClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Hello World")
}
}
WebTestClient can be used against both live servers and mock environments.
|
This setup requires spring-webflux
on the classpath.
If you can not or will not add webflux, Spring Boot also provides a TestRestTemplate
facility:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortTestRestTemplateTests {
@Test
void exampleTest(@Autowired TestRestTemplate restTemplate) {
String body = restTemplate.getForObject("/", String.class);
assertThat(body).isEqualTo("Hello World");
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortTestRestTemplateTests {
@Test
fun exampleTest(@Autowired restTemplate: TestRestTemplate) {
val body = restTemplate.getForObject("/", String::class.java)
assertThat(body).isEqualTo("Hello World")
}
}
8.3.7. Customizing WebTestClient
To customize the WebTestClient
bean, configure a WebTestClientBuilderCustomizer
bean.
Any such beans are called with the WebTestClient.Builder
that is used to create the WebTestClient
.
8.3.8. Using JMX
As the test context framework caches context, JMX is disabled by default to prevent identical components to register on the same domain.
If such test needs access to an MBeanServer
, consider marking it dirty as well:
@SpringBootTest(properties = "spring.jmx.enabled=true")
@DirtiesContext
class MyJmxTests {
@Autowired
private MBeanServer mBeanServer;
@Test
void exampleTest() {
assertThat(this.mBeanServer.getDomains()).contains("java.lang");
// ...
}
}
@SpringBootTest(properties = ["spring.jmx.enabled=true"])
@DirtiesContext
class MyJmxTests(@Autowired val mBeanServer: MBeanServer) {
@Test
fun exampleTest() {
assertThat(mBeanServer.domains).contains("java.lang")
// ...
}
}
8.3.9. Using Metrics
Regardless of your classpath, meter registries, except the in-memory backed, are not auto-configured when using @SpringBootTest
.
If you need to export metrics to a different backend as part of an integration test, annotate it with @AutoConfigureMetrics
.
8.3.10. Mocking and Spying Beans
When running tests, it is sometimes necessary to mock certain components within your application context. For example, you may have a facade over some remote service that is unavailable during development. Mocking can also be useful when you want to simulate failures that might be hard to trigger in a real environment.
Spring Boot includes a @MockBean
annotation that can be used to define a Mockito mock for a bean inside your ApplicationContext
.
You can use the annotation to add new beans or replace a single existing bean definition.
The annotation can be used directly on test classes, on fields within your test, or on @Configuration
classes and fields.
When used on a field, the instance of the created mock is also injected.
Mock beans are automatically reset after each test method.
If your test uses one of Spring Boot’s test annotations (such as Java
Kotlin
|
The following example replaces an existing RemoteService
bean with a mock implementation:
@SpringBootTest
class MyTests {
@Autowired
private Reverser reverser;
@MockBean
private RemoteService remoteService;
@Test
void exampleTest() {
given(this.remoteService.getValue()).willReturn("spring");
String reverse = this.reverser.getReverseValue(); // Calls injected RemoteService
assertThat(reverse).isEqualTo("gnirps");
}
}
@SpringBootTest
class MyTests(@Autowired val reverser: Reverser, @MockBean val remoteService: RemoteService) {
@Test
fun exampleTest() {
given(remoteService.value).willReturn("spring")
val reverse = reverser.reverseValue // Calls injected RemoteService
assertThat(reverse).isEqualTo("gnirps")
}
}
@MockBean cannot be used to mock the behavior of a bean that is exercised during application context refresh.
By the time the test is executed, the application context refresh has completed and it is too late to configure the mocked behavior.
We recommend using a @Bean method to create and configure the mock in this situation.
|
Additionally, you can use @SpyBean
to wrap any existing bean with a Mockito spy
.
See the Javadoc for full details.
CGLib proxies, such as those created for scoped beans, declare the proxied methods as final .
This stops Mockito from functioning correctly as it cannot mock or spy on final methods in its default configuration.
If you want to mock or spy on such a bean, configure Mockito to use its inline mock maker by adding org.mockito:mockito-inline to your application’s test dependencies.
This allows Mockito to mock and spy on final methods.
|
While Spring’s test framework caches application contexts between tests and reuses a context for tests sharing the same configuration, the use of @MockBean or @SpyBean influences the cache key, which will most likely increase the number of contexts.
|
If you are using @SpyBean to spy on a bean with @Cacheable methods that refer to parameters by name, your application must be compiled with -parameters .
This ensures that the parameter names are available to the caching infrastructure once the bean has been spied upon.
|
When you are using @SpyBean to spy on a bean that is proxied by Spring, you may need to remove Spring’s proxy in some situations, for example when setting expectations using given or when .
Use AopTestUtils.getTargetObject(yourProxiedSpy) to do so.
|
8.3.11. Auto-configured Tests
Spring Boot’s auto-configuration system works well for applications but can sometimes be a little too much for tests. It often helps to load only the parts of the configuration that are required to test a “slice” of your application. For example, you might want to test that Spring MVC controllers are mapping URLs correctly, and you do not want to involve database calls in those tests, or you might want to test JPA entities, and you are not interested in the web layer when those tests run.
The spring-boot-test-autoconfigure
module includes a number of annotations that can be used to automatically configure such “slices”.
Each of them works in a similar way, providing a @…Test
annotation that loads the ApplicationContext
and one or more @AutoConfigure…
annotations that can be used to customize auto-configuration settings.
Each slice restricts component scan to appropriate components and loads a very restricted set of auto-configuration classes.
If you need to exclude one of them, most @…Test annotations provide an excludeAutoConfiguration attribute.
Alternatively, you can use @ImportAutoConfiguration#exclude .
|
Including multiple “slices” by using several @…Test annotations in one test is not supported.
If you need multiple “slices”, pick one of the @…Test annotations and include the @AutoConfigure… annotations of the other “slices” by hand.
|
It is also possible to use the @AutoConfigure… annotations with the standard @SpringBootTest annotation.
You can use this combination if you are not interested in “slicing” your application but you want some of the auto-configured test beans.
|
8.3.12. Auto-configured JSON Tests
To test that object JSON serialization and deserialization is working as expected, you can use the @JsonTest
annotation.
@JsonTest
auto-configures the available supported JSON mapper, which can be one of the following libraries:
-
Jackson
ObjectMapper
, any@JsonComponent
beans and any JacksonModule
s -
Gson
-
Jsonb
A list of the auto-configurations that are enabled by @JsonTest can be found in the appendix.
|
If you need to configure elements of the auto-configuration, you can use the @AutoConfigureJsonTesters
annotation.
Spring Boot includes AssertJ-based helpers that work with the JSONAssert and JsonPath libraries to check that JSON appears as expected.
The JacksonTester
, GsonTester
, JsonbTester
, and BasicJsonTester
classes can be used for Jackson, Gson, Jsonb, and Strings respectively.
Any helper fields on the test class can be @Autowired
when using @JsonTest
.
The following example shows a test class for Jackson:
@JsonTest
class MyJsonTests {
@Autowired
private JacksonTester<VehicleDetails> json;
@Test
void serialize() throws Exception {
VehicleDetails details = new VehicleDetails("Honda", "Civic");
// Assert against a `.json` file in the same package as the test
assertThat(this.json.write(details)).isEqualToJson("expected.json");
// Or use JSON path based assertions
assertThat(this.json.write(details)).hasJsonPathStringValue("@.make");
assertThat(this.json.write(details)).extractingJsonPathStringValue("@.make").isEqualTo("Honda");
}
@Test
void deserialize() throws Exception {
String content = "{\"make\":\"Ford\",\"model\":\"Focus\"}";
assertThat(this.json.parse(content)).isEqualTo(new VehicleDetails("Ford", "Focus"));
assertThat(this.json.parseObject(content).getMake()).isEqualTo("Ford");
}
}
@JsonTest
class MyJsonTests(@Autowired val json: JacksonTester<VehicleDetails>) {
@Test
fun serialize() {
val details = VehicleDetails("Honda", "Civic")
// Assert against a `.json` file in the same package as the test
assertThat(json.write(details)).isEqualToJson("expected.json")
// Or use JSON path based assertions
assertThat(json.write(details)).hasJsonPathStringValue("@.make")
assertThat(json.write(details)).extractingJsonPathStringValue("@.make").isEqualTo("Honda")
}
@Test
fun deserialize() {
val content = "{\"make\":\"Ford\",\"model\":\"Focus\"}"
assertThat(json.parse(content)).isEqualTo(VehicleDetails("Ford", "Focus"))
assertThat(json.parseObject(content).make).isEqualTo("Ford")
}
}
JSON helper classes can also be used directly in standard unit tests.
To do so, call the initFields method of the helper in your @Before method if you do not use @JsonTest .
|
If you use Spring Boot’s AssertJ-based helpers to assert on a number value at a given JSON path, you might not be able to use isEqualTo
depending on the type.
Instead, you can use AssertJ’s satisfies
to assert that the value matches the given condition.
For instance, the following example asserts that the actual number is a float value close to 0.15
within an offset of 0.01
.
@Test
void someTest() throws Exception {
SomeObject value = new SomeObject(0.152f);
assertThat(this.json.write(value)).extractingJsonPathNumberValue("@.test.numberValue")
.satisfies((number) -> assertThat(number.floatValue()).isCloseTo(0.15f, within(0.01f)));
}
@Test
fun someTest() {
val value = SomeObject(0.152f)
assertThat(json.write(value)).extractingJsonPathNumberValue("@.test.numberValue")
.satisfies(ThrowingConsumer { number ->
assertThat(number.toFloat()).isCloseTo(0.15f, within(0.01f))
})
}
8.3.13. Auto-configured Spring MVC Tests
To test whether Spring MVC controllers are working as expected, use the @WebMvcTest
annotation.
@WebMvcTest
auto-configures the Spring MVC infrastructure and limits scanned beans to @Controller
, @ControllerAdvice
, @JsonComponent
, Converter
, GenericConverter
, Filter
, HandlerInterceptor
, WebMvcConfigurer
, WebMvcRegistrations
, and HandlerMethodArgumentResolver
.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @WebMvcTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configuration settings that are enabled by @WebMvcTest can be found in the appendix.
|
If you need to register extra components, such as the Jackson Module , you can import additional configuration classes by using @Import on your test.
|
Often, @WebMvcTest
is limited to a single controller and is used in combination with @MockBean
to provide mock implementations for required collaborators.
@WebMvcTest
also auto-configures MockMvc
.
Mock MVC offers a powerful way to quickly test MVC controllers without needing to start a full HTTP server.
You can also auto-configure MockMvc in a non-@WebMvcTest (such as @SpringBootTest ) by annotating it with @AutoConfigureMockMvc .
The following example uses MockMvc :
|
@WebMvcTest(UserVehicleController.class)
class MyControllerTests {
@Autowired
private MockMvc mvc;
@MockBean
private UserVehicleService userVehicleService;
@Test
void testExample() throws Exception {
given(this.userVehicleService.getVehicleDetails("sboot"))
.willReturn(new VehicleDetails("Honda", "Civic"));
this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
.andExpect(status().isOk())
.andExpect(content().string("Honda Civic"));
}
}
@WebMvcTest(UserVehicleController::class)
class MyControllerTests(@Autowired val mvc: MockMvc) {
@MockBean
lateinit var userVehicleService: UserVehicleService
@Test
fun testExample() {
given(userVehicleService.getVehicleDetails("sboot"))
.willReturn(VehicleDetails("Honda", "Civic"))
mvc.perform(MockMvcRequestBuilders.get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
.andExpect(MockMvcResultMatchers.status().isOk)
.andExpect(MockMvcResultMatchers.content().string("Honda Civic"))
}
}
If you need to configure elements of the auto-configuration (for example, when servlet filters should be applied) you can use attributes in the @AutoConfigureMockMvc annotation.
|
If you use HtmlUnit and Selenium, auto-configuration also provides an HtmlUnit WebClient
bean and/or a Selenium WebDriver
bean.
The following example uses HtmlUnit:
@WebMvcTest(UserVehicleController.class)
class MyHtmlUnitTests {
@Autowired
private WebClient webClient;
@MockBean
private UserVehicleService userVehicleService;
@Test
void testExample() throws Exception {
given(this.userVehicleService.getVehicleDetails("sboot")).willReturn(new VehicleDetails("Honda", "Civic"));
HtmlPage page = this.webClient.getPage("/sboot/vehicle.html");
assertThat(page.getBody().getTextContent()).isEqualTo("Honda Civic");
}
}
@WebMvcTest(UserVehicleController::class)
class MyHtmlUnitTests(@Autowired val webClient: WebClient) {
@MockBean
lateinit var userVehicleService: UserVehicleService
@Test
fun testExample() {
given(userVehicleService.getVehicleDetails("sboot")).willReturn(VehicleDetails("Honda", "Civic"))
val page = webClient.getPage<HtmlPage>("/sboot/vehicle.html")
assertThat(page.body.textContent).isEqualTo("Honda Civic")
}
}
By default, Spring Boot puts WebDriver beans in a special “scope” to ensure that the driver exits after each test and that a new instance is injected.
If you do not want this behavior, you can add @Scope("singleton") to your WebDriver @Bean definition.
|
The webDriver scope created by Spring Boot will replace any user defined scope of the same name.
If you define your own webDriver scope you may find it stops working when you use @WebMvcTest .
|
If you have Spring Security on the classpath, @WebMvcTest
will also scan WebSecurityConfigurer
beans.
Instead of disabling security completely for such tests, you can use Spring Security’s test support.
More details on how to use Spring Security’s MockMvc
support can be found in this howto.html how-to section.
Sometimes writing Spring MVC tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server. |
8.3.14. Auto-configured Spring WebFlux Tests
To test that Spring WebFlux controllers are working as expected, you can use the @WebFluxTest
annotation.
@WebFluxTest
auto-configures the Spring WebFlux infrastructure and limits scanned beans to @Controller
, @ControllerAdvice
, @JsonComponent
, Converter
, GenericConverter
, WebFilter
, and WebFluxConfigurer
.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @WebFluxTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configurations that are enabled by @WebFluxTest can be found in the appendix.
|
If you need to register extra components, such as Jackson Module , you can import additional configuration classes using @Import on your test.
|
Often, @WebFluxTest
is limited to a single controller and used in combination with the @MockBean
annotation to provide mock implementations for required collaborators.
@WebFluxTest
also auto-configures WebTestClient
, which offers a powerful way to quickly test WebFlux controllers without needing to start a full HTTP server.
You can also auto-configure WebTestClient in a non-@WebFluxTest (such as @SpringBootTest ) by annotating it with @AutoConfigureWebTestClient .
The following example shows a class that uses both @WebFluxTest and a WebTestClient :
|
@WebFluxTest(UserVehicleController.class)
class MyControllerTests {
@Autowired
private WebTestClient webClient;
@MockBean
private UserVehicleService userVehicleService;
@Test
void testExample() {
given(this.userVehicleService.getVehicleDetails("sboot"))
.willReturn(new VehicleDetails("Honda", "Civic"));
this.webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN).exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Honda Civic");
}
}
@WebFluxTest(UserVehicleController::class)
class MyControllerTests(@Autowired val webClient: WebTestClient) {
@MockBean
lateinit var userVehicleService: UserVehicleService
@Test
fun testExample() {
given(userVehicleService.getVehicleDetails("sboot"))
.willReturn(VehicleDetails("Honda", "Civic"))
webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN).exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Honda Civic")
}
}
This setup is only supported by WebFlux applications as using WebTestClient in a mocked web application only works with WebFlux at the moment.
|
@WebFluxTest cannot detect routes registered through the functional web framework.
For testing RouterFunction beans in the context, consider importing your RouterFunction yourself by using @Import or by using @SpringBootTest .
|
@WebFluxTest cannot detect custom security configuration registered as a @Bean of type SecurityWebFilterChain .
To include that in your test, you will need to import the configuration that registers the bean by using @Import or by using @SpringBootTest .
|
Sometimes writing Spring WebFlux tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server. |
8.3.15. Auto-configured Spring GraphQL Tests
Spring GraphQL offers a dedicated testing support module; you’ll need to add it to your project:
<dependencies>
<dependency>
<groupId>org.springframework.graphql</groupId>
<artifactId>spring-graphql-test</artifactId>
<scope>test</scope>
</dependency>
<!-- Unless already present in the compile scope -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
dependencies {
testImplementation("org.springframework.graphql:spring-graphql-test")
// Unless already present in the implementation configuration
testImplementation("org.springframework.boot:spring-boot-starter-webflux")
}
This testing module ships the GraphQlTester.
The tester is heavily used in test, so be sure to become familiar with using it.
There are GraphQlTester
variants and Spring Boot will auto-configure them depending on the type of tests:
-
the
ExecutionGraphQlServiceTester
performs tests on the server side, without a client nor a transport -
the
HttpGraphQlTester
performs tests with a client that connects to a server, with or without a live server
Spring Boot helps you to test your Spring GraphQL Controllers with the @GraphQlTest
annotation.
@GraphQlTest
auto-configures the Spring GraphQL infrastructure, without any transport nor server being involved.
This limits scanned beans to @Controller
, RuntimeWiringConfigurer
, JsonComponent
, Converter
, GenericConverter
, DataFetcherExceptionResolver
, Instrumentation
and GraphQlSourceBuilderCustomizer
.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @GraphQlTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configurations that are enabled by @GraphQlTest can be found in the appendix.
|
If you need to register extra components, such as Jackson Module , you can import additional configuration classes using @Import on your test.
|
Often, @GraphQlTest
is limited to a set of controllers and used in combination with the @MockBean
annotation to provide mock implementations for required collaborators.
@GraphQlTest(GreetingController.class)
class GreetingControllerTests {
@Autowired
private GraphQlTester graphQlTester;
@Test
void shouldGreetWithSpecificName() {
this.graphQlTester.document("{ greeting(name: \"Alice\") } ")
.execute()
.path("greeting")
.entity(String.class)
.isEqualTo("Hello, Alice!");
}
@Test
void shouldGreetWithDefaultName() {
this.graphQlTester.document("{ greeting } ")
.execute()
.path("greeting")
.entity(String.class)
.isEqualTo("Hello, Spring!");
}
}
@GraphQlTest(GreetingController::class)
internal class GreetingControllerTests {
@Autowired
lateinit var graphQlTester: GraphQlTester
@Test
fun shouldGreetWithSpecificName() {
graphQlTester.document("{ greeting(name: \"Alice\") } ").execute().path("greeting").entity(String::class.java)
.isEqualTo("Hello, Alice!")
}
@Test
fun shouldGreetWithDefaultName() {
graphQlTester.document("{ greeting } ").execute().path("greeting").entity(String::class.java)
.isEqualTo("Hello, Spring!")
}
}
@SpringBootTest
tests are full integration tests and involve the entire application.
When using a random or defined port, a live server is configured and an HttpGraphQlTester
bean is contributed automatically so you can use it to test your server.
When a MOCK environment is configured, you can also request an HttpGraphQlTester
bean by annotating your test class with @AutoConfigureHttpGraphQlTester
:
@AutoConfigureHttpGraphQlTester
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
class GraphQlIntegrationTests {
@Test
void shouldGreetWithSpecificName(@Autowired HttpGraphQlTester graphQlTester) {
HttpGraphQlTester authenticatedTester = graphQlTester.mutate()
.webTestClient((client) -> client.defaultHeaders((headers) -> headers.setBasicAuth("admin", "ilovespring")))
.build();
authenticatedTester.document("{ greeting(name: \"Alice\") } ")
.execute()
.path("greeting")
.entity(String.class)
.isEqualTo("Hello, Alice!");
}
}
@AutoConfigureHttpGraphQlTester
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
class GraphQlIntegrationTests {
@Test
fun shouldGreetWithSpecificName(@Autowired graphQlTester: HttpGraphQlTester) {
val authenticatedTester = graphQlTester.mutate()
.webTestClient { client: WebTestClient.Builder ->
client.defaultHeaders { headers: HttpHeaders ->
headers.setBasicAuth("admin", "ilovespring")
}
}.build()
authenticatedTester.document("{ greeting(name: \"Alice\") } ").execute()
.path("greeting").entity(String::class.java).isEqualTo("Hello, Alice!")
}
}
8.3.16. Auto-configured Data Cassandra Tests
You can use @DataCassandraTest
to test Cassandra applications.
By default, it configures a CassandraTemplate
, scans for @Table
classes, and configures Spring Data Cassandra repositories.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataCassandraTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
(For more about using Cassandra with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataCassandraTest can be found in the appendix.
|
The following example shows a typical setup for using Cassandra tests in Spring Boot:
@DataCassandraTest
class MyDataCassandraTests {
@Autowired
private SomeRepository repository;
}
@DataCassandraTest
class MyDataCassandraTests(@Autowired val repository: SomeRepository)
8.3.17. Auto-configured Data Couchbase Tests
You can use @DataCouchbaseTest
to test Couchbase applications.
By default, it configures a CouchbaseTemplate
or ReactiveCouchbaseTemplate
, scans for @Document
classes, and configures Spring Data Couchbase repositories.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataCouchbaseTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
(For more about using Couchbase with Spring Boot, see "data.html", earlier in this chapter.)
A list of the auto-configuration settings that are enabled by @DataCouchbaseTest can be found in the appendix.
|
The following example shows a typical setup for using Couchbase tests in Spring Boot:
@DataCouchbaseTest
class MyDataCouchbaseTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataCouchbaseTest
class MyDataCouchbaseTests(@Autowired val repository: SomeRepository) {
// ...
}
8.3.18. Auto-configured Data Elasticsearch Tests
You can use @DataElasticsearchTest
to test Elasticsearch applications.
By default, it configures an ElasticsearchRestTemplate
, scans for @Document
classes, and configures Spring Data Elasticsearch repositories.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataElasticsearchTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
(For more about using Elasticsearch with Spring Boot, see "data.html", earlier in this chapter.)
A list of the auto-configuration settings that are enabled by @DataElasticsearchTest can be found in the appendix.
|
The following example shows a typical setup for using Elasticsearch tests in Spring Boot:
@DataElasticsearchTest
class MyDataElasticsearchTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataElasticsearchTest
class MyDataElasticsearchTests(@Autowired val repository: SomeRepository) {
// ...
}
8.3.19. Auto-configured Data JPA Tests
You can use the @DataJpaTest
annotation to test JPA applications.
By default, it scans for @Entity
classes and configures Spring Data JPA repositories.
If an embedded database is available on the classpath, it configures one as well.
SQL queries are logged by default by setting the spring.jpa.show-sql
property to true
.
This can be disabled using the showSql()
attribute of the annotation.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataJpaTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configuration settings that are enabled by @DataJpaTest can be found in the appendix.
|
By default, data JPA tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class as follows:
@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyNonTransactionalTests {
// ...
}
@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyNonTransactionalTests {
// ...
}
Data JPA tests may also inject a TestEntityManager
bean, which provides an alternative to the standard JPA EntityManager
that is specifically designed for tests.
TestEntityManager can also be auto-configured to any of your Spring-based test class by adding @AutoConfigureTestEntityManager .
When doing so, make sure that your test is running in a transaction, for instance by adding @Transactional on your test class or method.
|
A JdbcTemplate
is also available if you need that.
The following example shows the @DataJpaTest
annotation in use:
@DataJpaTest
class MyRepositoryTests {
@Autowired
private TestEntityManager entityManager;
@Autowired
private UserRepository repository;
@Test
void testExample() {
this.entityManager.persist(new User("sboot", "1234"));
User user = this.repository.findByUsername("sboot");
assertThat(user.getUsername()).isEqualTo("sboot");
assertThat(user.getEmployeeNumber()).isEqualTo("1234");
}
}
@DataJpaTest
class MyRepositoryTests(@Autowired val entityManager: TestEntityManager, @Autowired val repository: UserRepository) {
@Test
fun testExample() {
entityManager.persist(User("sboot", "1234"))
val user = repository.findByUsername("sboot")
assertThat(user?.username).isEqualTo("sboot")
assertThat(user?.employeeNumber).isEqualTo("1234")
}
}
In-memory embedded databases generally work well for tests, since they are fast and do not require any installation.
If, however, you prefer to run tests against a real database you can use the @AutoConfigureTestDatabase
annotation, as shown in the following example:
@DataJpaTest
@AutoConfigureTestDatabase(replace = Replace.NONE)
class MyRepositoryTests {
// ...
}
@DataJpaTest
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
class MyRepositoryTests {
// ...
}
8.3.20. Auto-configured JDBC Tests
@JdbcTest
is similar to @DataJpaTest
but is for tests that only require a DataSource
and do not use Spring Data JDBC.
By default, it configures an in-memory embedded database and a JdbcTemplate
.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @JdbcTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configurations that are enabled by @JdbcTest can be found in the appendix.
|
By default, JDBC tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:
@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyTransactionalTests {
}
@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyTransactionalTests
If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase
annotation in the same way as for DataJpaTest
.
(See "Auto-configured Data JPA Tests".)
8.3.21. Auto-configured Data JDBC Tests
@DataJdbcTest
is similar to @JdbcTest
but is for tests that use Spring Data JDBC repositories.
By default, it configures an in-memory embedded database, a JdbcTemplate
, and Spring Data JDBC repositories.
Only AbstractJdbcConfiguration
sub-classes are scanned when the @DataJdbcTest
annotation is used, regular @Component
and @ConfigurationProperties
beans are not scanned.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configurations that are enabled by @DataJdbcTest can be found in the appendix.
|
By default, Data JDBC tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole test class as shown in the JDBC example.
If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase
annotation in the same way as for DataJpaTest
.
(See "Auto-configured Data JPA Tests".)
8.3.22. Auto-configured jOOQ Tests
You can use @JooqTest
in a similar fashion as @JdbcTest
but for jOOQ-related tests.
As jOOQ relies heavily on a Java-based schema that corresponds with the database schema, the existing DataSource
is used.
If you want to replace it with an in-memory database, you can use @AutoConfigureTestDatabase
to override those settings.
(For more about using jOOQ with Spring Boot, see "data.html".)
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @JooqTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configurations that are enabled by @JooqTest can be found in the appendix.
|
@JooqTest
configures a DSLContext
.
The following example shows the @JooqTest
annotation in use:
@JooqTest
class MyJooqTests {
@Autowired
private DSLContext dslContext;
// ...
}
@JooqTest
class MyJooqTests(@Autowired val dslContext: DSLContext) {
// ...
}
JOOQ tests are transactional and roll back at the end of each test by default. If that is not what you want, you can disable transaction management for a test or for the whole test class as shown in the JDBC example.
8.3.23. Auto-configured Data MongoDB Tests
You can use @DataMongoTest
to test MongoDB applications.
By default, it configures an in-memory embedded MongoDB (if available), configures a MongoTemplate
, scans for @Document
classes, and configures Spring Data MongoDB repositories.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataMongoTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
(For more about using MongoDB with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataMongoTest can be found in the appendix.
|
The following class shows the @DataMongoTest
annotation in use:
@DataMongoTest
class MyDataMongoDbTests {
@Autowired
private MongoTemplate mongoTemplate;
// ...
}
@DataMongoTest
class MyDataMongoDbTests(@Autowired val mongoTemplate: MongoTemplate) {
// ...
}
In-memory embedded MongoDB generally works well for tests, since it is fast and does not require any developer installation. If, however, you prefer to run tests against a real MongoDB server, you should exclude the embedded MongoDB auto-configuration, as shown in the following example:
@DataMongoTest(excludeAutoConfiguration = EmbeddedMongoAutoConfiguration.class)
class MyDataMongoDbTests {
// ...
}
@DataMongoTest(excludeAutoConfiguration = [EmbeddedMongoAutoConfiguration::class])
class MyDataMongoDbTests {
// ...
}
8.3.24. Auto-configured Data Neo4j Tests
You can use @DataNeo4jTest
to test Neo4j applications.
By default, it scans for @Node
classes, and configures Spring Data Neo4j repositories.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataNeo4jTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
(For more about using Neo4J with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataNeo4jTest can be found in the appendix.
|
The following example shows a typical setup for using Neo4J tests in Spring Boot:
@DataNeo4jTest
class MyDataNeo4jTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataNeo4jTest
class MyDataNeo4jTests(@Autowired val repository: SomeRepository) {
// ...
}
By default, Data Neo4j tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:
@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyDataNeo4jTests {
}
@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyDataNeo4jTests
Transactional tests are not supported with reactive access.
If you are using this style, you must configure @DataNeo4jTest tests as described above.
|
8.3.25. Auto-configured Data Redis Tests
You can use @DataRedisTest
to test Redis applications.
By default, it scans for @RedisHash
classes and configures Spring Data Redis repositories.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataRedisTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
(For more about using Redis with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataRedisTest can be found in the appendix.
|
The following example shows the @DataRedisTest
annotation in use:
@DataRedisTest
class MyDataRedisTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataRedisTest
class MyDataRedisTests(@Autowired val repository: SomeRepository) {
// ...
}
8.3.26. Auto-configured Data LDAP Tests
You can use @DataLdapTest
to test LDAP applications.
By default, it configures an in-memory embedded LDAP (if available), configures an LdapTemplate
, scans for @Entry
classes, and configures Spring Data LDAP repositories.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @DataLdapTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
(For more about using LDAP with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataLdapTest can be found in the appendix.
|
The following example shows the @DataLdapTest
annotation in use:
@DataLdapTest
class MyDataLdapTests {
@Autowired
private LdapTemplate ldapTemplate;
// ...
}
@DataLdapTest
class MyDataLdapTests(@Autowired val ldapTemplate: LdapTemplate) {
// ...
}
In-memory embedded LDAP generally works well for tests, since it is fast and does not require any developer installation. If, however, you prefer to run tests against a real LDAP server, you should exclude the embedded LDAP auto-configuration, as shown in the following example:
@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
class MyDataLdapTests {
// ...
}
@DataLdapTest(excludeAutoConfiguration = [EmbeddedLdapAutoConfiguration::class])
class MyDataLdapTests {
// ...
}
8.3.27. Auto-configured REST Clients
You can use the @RestClientTest
annotation to test REST clients.
By default, it auto-configures Jackson, GSON, and Jsonb support, configures a RestTemplateBuilder
, and adds support for MockRestServiceServer
.
Regular @Component
and @ConfigurationProperties
beans are not scanned when the @RestClientTest
annotation is used.
@EnableConfigurationProperties
can be used to include @ConfigurationProperties
beans.
A list of the auto-configuration settings that are enabled by @RestClientTest can be found in the appendix.
|
The specific beans that you want to test should be specified by using the value
or components
attribute of @RestClientTest
, as shown in the following example:
@RestClientTest(RemoteVehicleDetailsService.class)
class MyRestClientTests {
@Autowired
private RemoteVehicleDetailsService service;
@Autowired
private MockRestServiceServer server;
@Test
void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails() {
this.server.expect(requestTo("/greet/details")).andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
String greeting = this.service.callRestService();
assertThat(greeting).isEqualTo("hello");
}
}
@RestClientTest(RemoteVehicleDetailsService::class)
class MyRestClientTests(
@Autowired val service: RemoteVehicleDetailsService,
@Autowired val server: MockRestServiceServer) {
@Test
fun getVehicleDetailsWhenResultIsSuccessShouldReturnDetails(): Unit {
server.expect(MockRestRequestMatchers.requestTo("/greet/details"))
.andRespond(MockRestResponseCreators.withSuccess("hello", MediaType.TEXT_PLAIN))
val greeting = service.callRestService()
assertThat(greeting).isEqualTo("hello")
}
}
8.3.28. Auto-configured Spring REST Docs Tests
You can use the @AutoConfigureRestDocs
annotation to use Spring REST Docs in your tests with Mock MVC, REST Assured, or WebTestClient.
It removes the need for the JUnit extension in Spring REST Docs.
@AutoConfigureRestDocs
can be used to override the default output directory (target/generated-snippets
if you are using Maven or build/generated-snippets
if you are using Gradle).
It can also be used to configure the host, scheme, and port that appears in any documented URIs.
Auto-configured Spring REST Docs Tests With Mock MVC
@AutoConfigureRestDocs
customizes the MockMvc
bean to use Spring REST Docs when testing servlet-based web applications.
You can inject it by using @Autowired
and use it in your tests as you normally would when using Mock MVC and Spring REST Docs, as shown in the following example:
@WebMvcTest(UserController.class)
@AutoConfigureRestDocs
class MyUserDocumentationTests {
@Autowired
private MockMvc mvc;
@Test
void listUsers() throws Exception {
this.mvc.perform(get("/users").accept(MediaType.TEXT_PLAIN))
.andExpect(status().isOk())
.andDo(document("list-users"));
}
}
@WebMvcTest(UserController::class)
@AutoConfigureRestDocs
class MyUserDocumentationTests(@Autowired val mvc: MockMvc) {
@Test
fun listUsers() {
mvc.perform(MockMvcRequestBuilders.get("/users").accept(MediaType.TEXT_PLAIN))
.andExpect(MockMvcResultMatchers.status().isOk)
.andDo(MockMvcRestDocumentation.document("list-users"))
}
}
If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs
, you can use a RestDocsMockMvcConfigurationCustomizer
bean, as shown in the following example:
@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsMockMvcConfigurationCustomizer {
@Override
public void customize(MockMvcRestDocumentationConfigurer configurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsMockMvcConfigurationCustomizer {
override fun customize(configurer: MockMvcRestDocumentationConfigurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown())
}
}
If you want to make use of Spring REST Docs support for a parameterized output directory, you can create a RestDocumentationResultHandler
bean.
The auto-configuration calls alwaysDo
with this result handler, thereby causing each MockMvc
call to automatically generate the default snippets.
The following example shows a RestDocumentationResultHandler
being defined:
@TestConfiguration(proxyBeanMethods = false)
public class MyResultHandlerConfiguration {
@Bean
public RestDocumentationResultHandler restDocumentation() {
return MockMvcRestDocumentation.document("{method-name}");
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyResultHandlerConfiguration {
@Bean
fun restDocumentation(): RestDocumentationResultHandler {
return MockMvcRestDocumentation.document("{method-name}")
}
}
Auto-configured Spring REST Docs Tests With WebTestClient
@AutoConfigureRestDocs
can also be used with WebTestClient
when testing reactive web applications.
You can inject it by using @Autowired
and use it in your tests as you normally would when using @WebFluxTest
and Spring REST Docs, as shown in the following example:
@WebFluxTest
@AutoConfigureRestDocs
class MyUsersDocumentationTests {
@Autowired
private WebTestClient webTestClient;
@Test
void listUsers() {
this.webTestClient
.get().uri("/")
.exchange()
.expectStatus()
.isOk()
.expectBody()
.consumeWith(document("list-users"));
}
}
@WebFluxTest
@AutoConfigureRestDocs
class MyUsersDocumentationTests(@Autowired val webTestClient: WebTestClient) {
@Test
fun listUsers() {
webTestClient
.get().uri("/")
.exchange()
.expectStatus()
.isOk
.expectBody()
.consumeWith(WebTestClientRestDocumentation.document("list-users"))
}
}
If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs
, you can use a RestDocsWebTestClientConfigurationCustomizer
bean, as shown in the following example:
@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsWebTestClientConfigurationCustomizer {
@Override
public void customize(WebTestClientRestDocumentationConfigurer configurer) {
configurer.snippets().withEncoding("UTF-8");
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsWebTestClientConfigurationCustomizer {
override fun customize(configurer: WebTestClientRestDocumentationConfigurer) {
configurer.snippets().withEncoding("UTF-8")
}
}
If you want to make use of Spring REST Docs support for a parameterized output directory, you can use a WebTestClientBuilderCustomizer
to configure a consumer for every entity exchange result.
The following example shows such a WebTestClientBuilderCustomizer
being defined:
@TestConfiguration(proxyBeanMethods = false)
public class MyWebTestClientBuilderCustomizerConfiguration {
@Bean
public WebTestClientBuilderCustomizer restDocumentation() {
return (builder) -> builder.entityExchangeResultConsumer(document("{method-name}"));
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyWebTestClientBuilderCustomizerConfiguration {
@Bean
fun restDocumentation(): WebTestClientBuilderCustomizer {
return WebTestClientBuilderCustomizer { builder: WebTestClient.Builder ->
builder.entityExchangeResultConsumer(
WebTestClientRestDocumentation.document("{method-name}")
)
}
}
}
Auto-configured Spring REST Docs Tests With REST Assured
@AutoConfigureRestDocs
makes a RequestSpecification
bean, preconfigured to use Spring REST Docs, available to your tests.
You can inject it by using @Autowired
and use it in your tests as you normally would when using REST Assured and Spring REST Docs, as shown in the following example:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
class MyUserDocumentationTests {
@Test
void listUsers(@Autowired RequestSpecification documentationSpec, @LocalServerPort int port) {
given(documentationSpec)
.filter(document("list-users"))
.when()
.port(port)
.get("/")
.then().assertThat()
.statusCode(is(200));
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
class MyUserDocumentationTests {
@Test
fun listUsers(@Autowired documentationSpec: RequestSpecification?, @LocalServerPort port: Int) {
RestAssured.given(documentationSpec)
.filter(RestAssuredRestDocumentation.document("list-users"))
.`when`()
.port(port)["/"]
.then().assertThat()
.statusCode(Matchers.`is`(200))
}
}
If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs
, a RestDocsRestAssuredConfigurationCustomizer
bean can be used, as shown in the following example:
@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsRestAssuredConfigurationCustomizer {
@Override
public void customize(RestAssuredRestDocumentationConfigurer configurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsRestAssuredConfigurationCustomizer {
override fun customize(configurer: RestAssuredRestDocumentationConfigurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown())
}
}
8.3.29. Auto-configured Spring Web Services Tests
Auto-configured Spring Web Services Client Tests
You can use @WebServiceClientTest
to test applications that call web services using the Spring Web Services project.
By default, it configures a mock WebServiceServer
bean and automatically customizes your WebServiceTemplateBuilder
.
(For more about using Web Services with Spring Boot, see "io.html".)
A list of the auto-configuration settings that are enabled by @WebServiceClientTest can be found in the appendix.
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The following example shows the @WebServiceClientTest
annotation in use:
@WebServiceClientTest(SomeWebService.class)
class MyWebServiceClientTests {
@Autowired
private MockWebServiceServer server;
@Autowired
private SomeWebService someWebService;
@Test
void mockServerCall() {
this.server
.expect(payload(new StringSource("<request/>")))
.andRespond(withPayload(new StringSource("<response><status>200</status></response>")));
assertThat(this.someWebService.test())
.extracting(Response::getStatus)
.isEqualTo(200);
}
}
@WebServiceClientTest(SomeWebService::class)
class MyWebServiceClientTests(@Autowired val server: MockWebServiceServer, @Autowired val someWebService: SomeWebService) {
@Test
fun mockServerCall() {
server
.expect(RequestMatchers.payload(StringSource("<request/>")))
.andRespond(ResponseCreators.withPayload(StringSource("<response><status>200</status></response>")))
assertThat(this.someWebService.test()).extracting(Response::status).isEqualTo(200)
}
}
Auto-configured Spring Web Services Server Tests
You can use @WebServiceServerTest
to test applications that implement web services using the Spring Web Services project.
By default, it configures a MockWebServiceClient
bean that can be used to call your web service endpoints.
(For more about using Web Services with Spring Boot, see "io.html".)
A list of the auto-configuration settings that are enabled by @WebServiceServerTest can be found in the appendix.
|
The following example shows the @WebServiceServerTest
annotation in use:
@WebServiceServerTest(ExampleEndpoint.class)
class MyWebServiceServerTests {
@Autowired
private MockWebServiceClient client;
@Test
void mockServerCall() {
this.client
.sendRequest(RequestCreators.withPayload(new StringSource("<ExampleRequest/>")))
.andExpect(ResponseMatchers.payload(new StringSource("<ExampleResponse>42</ExampleResponse>")));
}
}
@WebServiceServerTest(ExampleEndpoint::class)
class MyWebServiceServerTests(@Autowired val client: MockWebServiceClient) {
@Test
fun mockServerCall() {
client
.sendRequest(RequestCreators.withPayload(StringSource("<ExampleRequest/>")))
.andExpect(ResponseMatchers.payload(StringSource("<ExampleResponse>42</ExampleResponse>")))
}
}
8.3.30. Additional Auto-configuration and Slicing
Each slice provides one or more @AutoConfigure…
annotations that namely defines the auto-configurations that should be included as part of a slice.
Additional auto-configurations can be added on a test-by-test basis by creating a custom @AutoConfigure…
annotation or by adding @ImportAutoConfiguration
to the test as shown in the following example:
@JdbcTest
@ImportAutoConfiguration(IntegrationAutoConfiguration.class)
class MyJdbcTests {
}
@JdbcTest
@ImportAutoConfiguration(IntegrationAutoConfiguration::class)
class MyJdbcTests
Make sure to not use the regular @Import annotation to import auto-configurations as they are handled in a specific way by Spring Boot.
|
Alternatively, additional auto-configurations can be added for any use of a slice annotation by registering them in a file stored in META-INF/spring
as shown in the following example:
com.example.IntegrationAutoConfiguration
In this example, the com.example.IntegrationAutoConfiguration
is enabled on every test annotated with @JdbcTest
.
You can use comments with # in this file.
|
A slice or @AutoConfigure… annotation can be customized this way as long as it is meta-annotated with @ImportAutoConfiguration .
|
8.3.31. User Configuration and Slicing
If you structure your code in a sensible way, your @SpringBootApplication
class is used by default as the configuration of your tests.
It then becomes important not to litter the application’s main class with configuration settings that are specific to a particular area of its functionality.
Assume that you are using Spring Batch and you rely on the auto-configuration for it.
You could define your @SpringBootApplication
as follows:
@SpringBootApplication
@EnableBatchProcessing
public class MyApplication {
// ...
}
@SpringBootApplication
@EnableBatchProcessing
class MyApplication {
// ...
}
Because this class is the source configuration for the test, any slice test actually tries to start Spring Batch, which is definitely not what you want to do.
A recommended approach is to move that area-specific configuration to a separate @Configuration
class at the same level as your application, as shown in the following example:
@Configuration(proxyBeanMethods = false)
@EnableBatchProcessing
public class MyBatchConfiguration {
// ...
}
@Configuration(proxyBeanMethods = false)
@EnableBatchProcessing
class MyBatchConfiguration {
// ...
}
Depending on the complexity of your application, you may either have a single @Configuration class for your customizations or one class per domain area.
The latter approach lets you enable it in one of your tests, if necessary, with the @Import annotation.
See this how-to section for more details on when you might want to enable specific @Configuration classes for slice tests.
|
Test slices exclude @Configuration
classes from scanning.
For example, for a @WebMvcTest
, the following configuration will not include the given WebMvcConfigurer
bean in the application context loaded by the test slice:
@Configuration(proxyBeanMethods = false)
public class MyWebConfiguration {
@Bean
public WebMvcConfigurer testConfigurer() {
return new WebMvcConfigurer() {
// ...
};
}
}
@Configuration(proxyBeanMethods = false)
class MyWebConfiguration {
@Bean
fun testConfigurer(): WebMvcConfigurer {
return object : WebMvcConfigurer {
// ...
}
}
}
The configuration below will, however, cause the custom WebMvcConfigurer
to be loaded by the test slice.
@Component
public class MyWebMvcConfigurer implements WebMvcConfigurer {
// ...
}
@Component
class MyWebMvcConfigurer : WebMvcConfigurer {
// ...
}
Another source of confusion is classpath scanning. Assume that, while you structured your code in a sensible way, you need to scan an additional package. Your application may resemble the following code:
@SpringBootApplication
@ComponentScan({ "com.example.app", "com.example.another" })
public class MyApplication {
// ...
}
@SpringBootApplication
@ComponentScan("com.example.app", "com.example.another")
class MyApplication {
// ...
}
Doing so effectively overrides the default component scan directive with the side effect of scanning those two packages regardless of the slice that you chose.
For instance, a @DataJpaTest
seems to suddenly scan components and user configurations of your application.
Again, moving the custom directive to a separate class is a good way to fix this issue.
If this is not an option for you, you can create a @SpringBootConfiguration somewhere in the hierarchy of your test so that it is used instead.
Alternatively, you can specify a source for your test, which disables the behavior of finding a default one.
|
8.3.32. Using Spock to Test Spring Boot Applications
Spock 2.x can be used to test a Spring Boot application.
To do so, add a dependency on Spock’s spock-spring
module to your application’s build.
spock-spring
integrates Spring’s test framework into Spock.
See the documentation for Spock’s Spring module for further details.
8.4. Test Utilities
A few test utility classes that are generally useful when testing your application are packaged as part of spring-boot
.
8.4.1. ConfigDataApplicationContextInitializer
ConfigDataApplicationContextInitializer
is an ApplicationContextInitializer
that you can apply to your tests to load Spring Boot application.properties
files.
You can use it when you do not need the full set of features provided by @SpringBootTest
, as shown in the following example:
@ContextConfiguration(classes = Config.class, initializers = ConfigDataApplicationContextInitializer.class)
class MyConfigFileTests {
// ...
}
@ContextConfiguration(classes = [Config::class], initializers = [ConfigDataApplicationContextInitializer::class])
class MyConfigFileTests {
// ...
}
Using ConfigDataApplicationContextInitializer alone does not provide support for @Value("${…}") injection.
Its only job is to ensure that application.properties files are loaded into Spring’s Environment .
For @Value support, you need to either additionally configure a PropertySourcesPlaceholderConfigurer or use @SpringBootTest , which auto-configures one for you.
|
8.4.2. TestPropertyValues
TestPropertyValues
lets you quickly add properties to a ConfigurableEnvironment
or ConfigurableApplicationContext
.
You can call it with key=value
strings, as follows:
class MyEnvironmentTests {
@Test
void testPropertySources() {
MockEnvironment environment = new MockEnvironment();
TestPropertyValues.of("org=Spring", "name=Boot").applyTo(environment);
assertThat(environment.getProperty("name")).isEqualTo("Boot");
}
}
class MyEnvironmentTests {
@Test
fun testPropertySources() {
val environment = MockEnvironment()
TestPropertyValues.of("org=Spring", "name=Boot").applyTo(environment)
assertThat(environment.getProperty("name")).isEqualTo("Boot")
}
}
8.4.3. OutputCapture
OutputCapture
is a JUnit Extension
that you can use to capture System.out
and System.err
output.
To use add @ExtendWith(OutputCaptureExtension.class)
and inject CapturedOutput
as an argument to your test class constructor or test method as follows:
@ExtendWith(OutputCaptureExtension.class)
class MyOutputCaptureTests {
@Test
void testName(CapturedOutput output) {
System.out.println("Hello World!");
assertThat(output).contains("World");
}
}
@ExtendWith(OutputCaptureExtension::class)
class MyOutputCaptureTests {
@Test
fun testName(output: CapturedOutput?) {
println("Hello World!")
assertThat(output).contains("World")
}
}
8.4.4. TestRestTemplate
TestRestTemplate
is a convenience alternative to Spring’s RestTemplate
that is useful in integration tests.
You can get a vanilla template or one that sends Basic HTTP authentication (with a username and password).
In either case, the template is fault tolerant.
This means that it behaves in a test-friendly way by not throwing exceptions on 4xx and 5xx errors.
Instead, such errors can be detected through the returned ResponseEntity
and its status code.
Spring Framework 5.0 provides a new WebTestClient that works for WebFlux integration tests and both WebFlux and MVC end-to-end testing.
It provides a fluent API for assertions, unlike TestRestTemplate .
|
It is recommended, but not mandatory, to use the Apache HTTP Client (version 4.3.2 or better).
If you have that on your classpath, the TestRestTemplate
responds by configuring the client appropriately.
If you do use Apache’s HTTP client, some additional test-friendly features are enabled:
-
Redirects are not followed (so you can assert the response location).
-
Cookies are ignored (so the template is stateless).
TestRestTemplate
can be instantiated directly in your integration tests, as shown in the following example:
class MyTests {
private final TestRestTemplate template = new TestRestTemplate();
@Test
void testRequest() {
ResponseEntity<String> headers = this.template.getForEntity("https://myhost.example.com/example", String.class);
assertThat(headers.getHeaders().getLocation()).hasHost("other.example.com");
}
}
class MyTests {
private val template = TestRestTemplate()
@Test
fun testRequest() {
val headers = template.getForEntity("https://myhost.example.com/example", String::class.java)
assertThat(headers.headers.location).hasHost("other.example.com")
}
}
Alternatively, if you use the @SpringBootTest
annotation with WebEnvironment.RANDOM_PORT
or WebEnvironment.DEFINED_PORT
, you can inject a fully configured TestRestTemplate
and start using it.
If necessary, additional customizations can be applied through the RestTemplateBuilder
bean.
Any URLs that do not specify a host and port automatically connect to the embedded server, as shown in the following example:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MySpringBootTests {
@Autowired
private TestRestTemplate template;
@Test
void testRequest() {
HttpHeaders headers = this.template.getForEntity("/example", String.class).getHeaders();
assertThat(headers.getLocation()).hasHost("other.example.com");
}
@TestConfiguration(proxyBeanMethods = false)
static class RestTemplateBuilderConfiguration {
@Bean
RestTemplateBuilder restTemplateBuilder() {
return new RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
.setReadTimeout(Duration.ofSeconds(1));
}
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MySpringBootTests(@Autowired val template: TestRestTemplate) {
@Test
fun testRequest() {
val headers = template.getForEntity("/example", String::class.java).headers
assertThat(headers.location).hasHost("other.example.com")
}
@TestConfiguration(proxyBeanMethods = false)
internal class RestTemplateBuilderConfiguration {
@Bean
fun restTemplateBuilder(): RestTemplateBuilder {
return RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
.setReadTimeout(Duration.ofSeconds(1))
}
}
}
9. Creating Your Own Auto-configuration
If you work in a company that develops shared libraries, or if you work on an open-source or commercial library, you might want to develop your own auto-configuration. Auto-configuration classes can be bundled in external jars and still be picked-up by Spring Boot.
Auto-configuration can be associated to a “starter” that provides the auto-configuration code as well as the typical libraries that you would use with it. We first cover what you need to know to build your own auto-configuration and then we move on to the typical steps required to create a custom starter.
9.1. Understanding Auto-configured Beans
Classes that implement auto-configuration are annotated with @AutoConfiguration
.
This annotation itself is meta-annotated with @Configuration
, making auto-configurations standard @Configuration
classes.
Additional @Conditional
annotations are used to constrain when the auto-configuration should apply.
Usually, auto-configuration classes use @ConditionalOnClass
and @ConditionalOnMissingBean
annotations.
This ensures that auto-configuration applies only when relevant classes are found and when you have not declared your own @Configuration
.
You can browse the source code of spring-boot-autoconfigure
to see the @AutoConfiguration
classes that Spring provides (see the META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports
file).
9.2. Locating Auto-configuration Candidates
Spring Boot checks for the presence of a META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports
file within your published jar.
The file should list your configuration classes, with one class name per line, as shown in the following example:
com.mycorp.libx.autoconfigure.LibXAutoConfiguration com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration
You can add comments to the imports file using the # character.
|
Auto-configurations must be loaded only by being named in the imports file.
Make sure that they are defined in a specific package space and that they are never the target of component scanning.
Furthermore, auto-configuration classes should not enable component scanning to find additional components.
Specific @Import s should be used instead.
|
If your configuration needs to be applied in a specific order, you can use the before
, beforeName
, after
and afterName
attributes on the @AutoConfiguration
annotation or the dedicated @AutoConfigureBefore
and @AutoConfigureAfter
annotations.
For example, if you provide web-specific configuration, your class may need to be applied after WebMvcAutoConfiguration
.
If you want to order certain auto-configurations that should not have any direct knowledge of each other, you can also use @AutoConfigureOrder
.
That annotation has the same semantic as the regular @Order
annotation but provides a dedicated order for auto-configuration classes.
As with standard @Configuration
classes, the order in which auto-configuration classes are applied only affects the order in which their beans are defined.
The order in which those beans are subsequently created is unaffected and is determined by each bean’s dependencies and any @DependsOn
relationships.
9.3. Condition Annotations
You almost always want to include one or more @Conditional
annotations on your auto-configuration class.
The @ConditionalOnMissingBean
annotation is one common example that is used to allow developers to override auto-configuration if they are not happy with your defaults.
Spring Boot includes a number of @Conditional
annotations that you can reuse in your own code by annotating @Configuration
classes or individual @Bean
methods.
These annotations include:
9.3.1. Class Conditions
The @ConditionalOnClass
and @ConditionalOnMissingClass
annotations let @Configuration
classes be included based on the presence or absence of specific classes.
Due to the fact that annotation metadata is parsed by using ASM, you can use the value
attribute to refer to the real class, even though that class might not actually appear on the running application classpath.
You can also use the name
attribute if you prefer to specify the class name by using a String
value.
This mechanism does not apply the same way to @Bean
methods where typically the return type is the target of the condition: before the condition on the method applies, the JVM will have loaded the class and potentially processed method references which will fail if the class is not present.
To handle this scenario, a separate @Configuration
class can be used to isolate the condition, as shown in the following example:
@AutoConfiguration
// Some conditions ...
public class MyAutoConfiguration {
// Auto-configured beans ...
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(SomeService.class)
public static class SomeServiceConfiguration {
@Bean
@ConditionalOnMissingBean
public SomeService someService() {
return new SomeService();
}
}
}
@Configuration(proxyBeanMethods = false)
// Some conditions ...
class MyAutoConfiguration {
// Auto-configured beans ...
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(SomeService::class)
class SomeServiceConfiguration {
@Bean
@ConditionalOnMissingBean
fun someService(): SomeService {
return SomeService()
}
}
}
If you use @ConditionalOnClass or @ConditionalOnMissingClass as a part of a meta-annotation to compose your own composed annotations, you must use name as referring to the class in such a case is not handled.
|
9.3.2. Bean Conditions
The @ConditionalOnBean
and @ConditionalOnMissingBean
annotations let a bean be included based on the presence or absence of specific beans.
You can use the value
attribute to specify beans by type or name
to specify beans by name.
The search
attribute lets you limit the ApplicationContext
hierarchy that should be considered when searching for beans.
When placed on a @Bean
method, the target type defaults to the return type of the method, as shown in the following example:
@AutoConfiguration
public class MyAutoConfiguration {
@Bean
@ConditionalOnMissingBean
public SomeService someService() {
return new SomeService();
}
}
@Configuration(proxyBeanMethods = false)
class MyAutoConfiguration {
@Bean
@ConditionalOnMissingBean
fun someService(): SomeService {
return SomeService()
}
}
In the preceding example, the someService
bean is going to be created if no bean of type SomeService
is already contained in the ApplicationContext
.
You need to be very careful about the order in which bean definitions are added, as these conditions are evaluated based on what has been processed so far.
For this reason, we recommend using only @ConditionalOnBean and @ConditionalOnMissingBean annotations on auto-configuration classes (since these are guaranteed to load after any user-defined bean definitions have been added).
|
@ConditionalOnBean and @ConditionalOnMissingBean do not prevent @Configuration classes from being created.
The only difference between using these conditions at the class level and marking each contained @Bean method with the annotation is that the former prevents registration of the @Configuration class as a bean if the condition does not match.
|
When declaring a @Bean method, provide as much type information as possible in the method’s return type.
For example, if your bean’s concrete class implements an interface the bean method’s return type should be the concrete class and not the interface.
Providing as much type information as possible in @Bean methods is particularly important when using bean conditions as their evaluation can only rely upon to type information that is available in the method signature.
|
9.3.3. Property Conditions
The @ConditionalOnProperty
annotation lets configuration be included based on a Spring Environment property.
Use the prefix
and name
attributes to specify the property that should be checked.
By default, any property that exists and is not equal to false
is matched.
You can also create more advanced checks by using the havingValue
and matchIfMissing
attributes.
9.3.4. Resource Conditions
The @ConditionalOnResource
annotation lets configuration be included only when a specific resource is present.
Resources can be specified by using the usual Spring conventions, as shown in the following example: file:/home/user/test.dat
.
9.3.5. Web Application Conditions
The @ConditionalOnWebApplication
and @ConditionalOnNotWebApplication
annotations let configuration be included depending on whether the application is a “web application”.
A servlet-based web application is any application that uses a Spring WebApplicationContext
, defines a session
scope, or has a ConfigurableWebEnvironment
.
A reactive web application is any application that uses a ReactiveWebApplicationContext
, or has a ConfigurableReactiveWebEnvironment
.
The @ConditionalOnWarDeployment
annotation lets configuration be included depending on whether the application is a traditional WAR application that is deployed to a container.
This condition will not match for applications that are run with an embedded server.
9.3.6. SpEL Expression Conditions
The @ConditionalOnExpression
annotation lets configuration be included based on the result of a SpEL expression.
Referencing a bean in the expression will cause that bean to be initialized very early in context refresh processing. As a result, the bean won’t be eligible for post-processing (such as configuration properties binding) and its state may be incomplete. |
9.4. Testing your Auto-configuration
An auto-configuration can be affected by many factors: user configuration (@Bean
definition and Environment
customization), condition evaluation (presence of a particular library), and others.
Concretely, each test should create a well defined ApplicationContext
that represents a combination of those customizations.
ApplicationContextRunner
provides a great way to achieve that.
ApplicationContextRunner
is usually defined as a field of the test class to gather the base, common configuration.
The following example makes sure that MyServiceAutoConfiguration
is always invoked:
private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
.withConfiguration(AutoConfigurations.of(MyServiceAutoConfiguration.class));
val contextRunner = ApplicationContextRunner()
.withConfiguration(AutoConfigurations.of(MyServiceAutoConfiguration::class.java))
If multiple auto-configurations have to be defined, there is no need to order their declarations as they are invoked in the exact same order as when running the application. |
Each test can use the runner to represent a particular use case.
For instance, the sample below invokes a user configuration (UserConfiguration
) and checks that the auto-configuration backs off properly.
Invoking run
provides a callback context that can be used with AssertJ
.
@Test
void defaultServiceBacksOff() {
this.contextRunner.withUserConfiguration(UserConfiguration.class).run((context) -> {
assertThat(context).hasSingleBean(MyService.class);
assertThat(context).getBean("myCustomService").isSameAs(context.getBean(MyService.class));
});
}
@Configuration(proxyBeanMethods = false)
static class UserConfiguration {
@Bean
MyService myCustomService() {
return new MyService("mine");
}
}
@Test
fun defaultServiceBacksOff() {
contextRunner.withUserConfiguration(UserConfiguration::class.java)
.run { context: AssertableApplicationContext ->
assertThat(context).hasSingleBean(MyService::class.java)
assertThat(context).getBean("myCustomService")
.isSameAs(context.getBean(MyService::class.java))
}
}
@Configuration(proxyBeanMethods = false)
internal class UserConfiguration {
@Bean
fun myCustomService(): MyService {
return MyService("mine")
}
}
It is also possible to easily customize the Environment
, as shown in the following example:
@Test
void serviceNameCanBeConfigured() {
this.contextRunner.withPropertyValues("user.name=test123").run((context) -> {
assertThat(context).hasSingleBean(MyService.class);
assertThat(context.getBean(MyService.class).getName()).isEqualTo("test123");
});
}
@Test
fun serviceNameCanBeConfigured() {
contextRunner.withPropertyValues("user.name=test123").run { context: AssertableApplicationContext ->
assertThat(context).hasSingleBean(MyService::class.java)
assertThat(context.getBean(MyService::class.java).name).isEqualTo("test123")
}
}
The runner can also be used to display the ConditionEvaluationReport
.
The report can be printed at INFO
or DEBUG
level.
The following example shows how to use the ConditionEvaluationReportLoggingListener
to print the report in auto-configuration tests.
class MyConditionEvaluationReportingTests {
@Test
void autoConfigTest() {
new ApplicationContextRunner()
.withInitializer(new ConditionEvaluationReportLoggingListener(LogLevel.INFO))
.run((context) -> {
// Test something...
});
}
}
class MyConditionEvaluationReportingTests {
@Test
fun autoConfigTest() {
ApplicationContextRunner()
.withInitializer(ConditionEvaluationReportLoggingListener(LogLevel.INFO))
.run { context: AssertableApplicationContext? -> }
}
}
9.4.1. Simulating a Web Context
If you need to test an auto-configuration that only operates in a servlet or reactive web application context, use the WebApplicationContextRunner
or ReactiveWebApplicationContextRunner
respectively.
9.4.2. Overriding the Classpath
It is also possible to test what happens when a particular class and/or package is not present at runtime.
Spring Boot ships with a FilteredClassLoader
that can easily be used by the runner.
In the following example, we assert that if MyService
is not present, the auto-configuration is properly disabled:
@Test
void serviceIsIgnoredIfLibraryIsNotPresent() {
this.contextRunner.withClassLoader(new FilteredClassLoader(MyService.class))
.run((context) -> assertThat(context).doesNotHaveBean("myService"));
}
@Test
fun serviceIsIgnoredIfLibraryIsNotPresent() {
contextRunner.withClassLoader(FilteredClassLoader(MyService::class.java))
.run { context: AssertableApplicationContext? ->
assertThat(context).doesNotHaveBean("myService")
}
}
9.5. Creating Your Own Starter
A typical Spring Boot starter contains code to auto-configure and customize the infrastructure of a given technology, let’s call that "acme". To make it easily extensible, a number of configuration keys in a dedicated namespace can be exposed to the environment. Finally, a single "starter" dependency is provided to help users get started as easily as possible.
Concretely, a custom starter can contain the following:
-
The
autoconfigure
module that contains the auto-configuration code for "acme". -
The
starter
module that provides a dependency to theautoconfigure
module as well as "acme" and any additional dependencies that are typically useful. In a nutshell, adding the starter should provide everything needed to start using that library.
This separation in two modules is in no way necessary.
If "acme" has several flavors, options or optional features, then it is better to separate the auto-configuration as you can clearly express the fact some features are optional.
Besides, you have the ability to craft a starter that provides an opinion about those optional dependencies.
At the same time, others can rely only on the autoconfigure
module and craft their own starter with different opinions.
If the auto-configuration is relatively straightforward and does not have optional feature, merging the two modules in the starter is definitely an option.
9.5.1. Naming
You should make sure to provide a proper namespace for your starter.
Do not start your module names with spring-boot
, even if you use a different Maven groupId
.
We may offer official support for the thing you auto-configure in the future.
As a rule of thumb, you should name a combined module after the starter.
For example, assume that you are creating a starter for "acme" and that you name the auto-configure module acme-spring-boot
and the starter acme-spring-boot-starter
.
If you only have one module that combines the two, name it acme-spring-boot-starter
.
9.5.2. Configuration keys
If your starter provides configuration keys, use a unique namespace for them.
In particular, do not include your keys in the namespaces that Spring Boot uses (such as server
, management
, spring
, and so on).
If you use the same namespace, we may modify these namespaces in the future in ways that break your modules.
As a rule of thumb, prefix all your keys with a namespace that you own (for example acme
).
Make sure that configuration keys are documented by adding field javadoc for each property, as shown in the following example:
@ConfigurationProperties("acme")
public class AcmeProperties {
/**
* Whether to check the location of acme resources.
*/
private boolean checkLocation = true;
/**
* Timeout for establishing a connection to the acme server.
*/
private Duration loginTimeout = Duration.ofSeconds(3);
}
@ConfigurationProperties("acme")
class AcmeProperties(
/**
* Whether to check the location of acme resources.
*/
var isCheckLocation: Boolean = true,
/**
* Timeout for establishing a connection to the acme server.
*/
var loginTimeout:Duration = Duration.ofSeconds(3))
You should only use plain text with @ConfigurationProperties field Javadoc, since they are not processed before being added to the JSON.
|
Here are some rules we follow internally to make sure descriptions are consistent:
-
Do not start the description by "The" or "A".
-
For
boolean
types, start the description with "Whether" or "Enable". -
For collection-based types, start the description with "Comma-separated list"
-
Use
java.time.Duration
rather thanlong
and describe the default unit if it differs from milliseconds, such as "If a duration suffix is not specified, seconds will be used". -
Do not provide the default value in the description unless it has to be determined at runtime.
Make sure to trigger meta-data generation so that IDE assistance is available for your keys as well.
You may want to review the generated metadata (META-INF/spring-configuration-metadata.json
) to make sure your keys are properly documented.
Using your own starter in a compatible IDE is also a good idea to validate that quality of the metadata.
9.5.3. The “autoconfigure” Module
The autoconfigure
module contains everything that is necessary to get started with the library.
It may also contain configuration key definitions (such as @ConfigurationProperties
) and any callback interface that can be used to further customize how the components are initialized.
You should mark the dependencies to the library as optional so that you can include the autoconfigure module in your projects more easily.
If you do it that way, the library is not provided and, by default, Spring Boot backs off.
|
Spring Boot uses an annotation processor to collect the conditions on auto-configurations in a metadata file (META-INF/spring-autoconfigure-metadata.properties
).
If that file is present, it is used to eagerly filter auto-configurations that do not match, which will improve startup time.
When building with Maven, it is recommended to add the following dependency in a module that contains auto-configurations:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-autoconfigure-processor</artifactId>
<optional>true</optional>
</dependency>
If you have defined auto-configurations directly in your application, make sure to configure the spring-boot-maven-plugin
to prevent the repackage
goal from adding the dependency into the fat jar:
<project>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-autoconfigure-processor</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
</project>
With Gradle, the dependency should be declared in the annotationProcessor
configuration, as shown in the following example:
dependencies {
annotationProcessor "org.springframework.boot:spring-boot-autoconfigure-processor"
}
9.5.4. Starter Module
The starter is really an empty jar. Its only purpose is to provide the necessary dependencies to work with the library. You can think of it as an opinionated view of what is required to get started.
Do not make assumptions about the project in which your starter is added. If the library you are auto-configuring typically requires other starters, mention them as well. Providing a proper set of default dependencies may be hard if the number of optional dependencies is high, as you should avoid including dependencies that are unnecessary for a typical usage of the library. In other words, you should not include optional dependencies.
Either way, your starter must reference the core Spring Boot starter (spring-boot-starter ) directly or indirectly (there is no need to add it if your starter relies on another starter).
If a project is created with only your custom starter, Spring Boot’s core features will be honoured by the presence of the core starter.
|
10. Kotlin Support
Kotlin is a statically-typed language targeting the JVM (and other platforms) which allows writing concise and elegant code while providing interoperability with existing libraries written in Java.
Spring Boot provides Kotlin support by leveraging the support in other Spring projects such as Spring Framework, Spring Data, and Reactor. See the Spring Framework Kotlin support documentation for more information.
The easiest way to start with Spring Boot and Kotlin is to follow this comprehensive tutorial.
You can create new Kotlin projects by using start.spring.io.
Feel free to join the #spring channel of Kotlin Slack or ask a question with the spring
and kotlin
tags on Stack Overflow if you need support.
10.1. Requirements
Spring Boot requires at least Kotlin 1.3.x and manages a suitable Kotlin version through dependency management.
To use Kotlin, org.jetbrains.kotlin:kotlin-stdlib
and org.jetbrains.kotlin:kotlin-reflect
must be present on the classpath.
The kotlin-stdlib
variants kotlin-stdlib-jdk7
and kotlin-stdlib-jdk8
can also be used.
Since Kotlin classes are final by default, you are likely to want to configure kotlin-spring plugin in order to automatically open Spring-annotated classes so that they can be proxied.
Jackson’s Kotlin module is required for serializing / deserializing JSON data in Kotlin. It is automatically registered when found on the classpath. A warning message is logged if Jackson and Kotlin are present but the Jackson Kotlin module is not.
These dependencies and plugins are provided by default if one bootstraps a Kotlin project on start.spring.io. |
10.2. Null-safety
One of Kotlin’s key features is null-safety.
It deals with null
values at compile time rather than deferring the problem to runtime and encountering a NullPointerException
.
This helps to eliminate a common source of bugs without paying the cost of wrappers like Optional
.
Kotlin also allows using functional constructs with nullable values as described in this comprehensive guide to null-safety in Kotlin.
Although Java does not allow one to express null-safety in its type system, Spring Framework, Spring Data, and Reactor now provide null-safety of their API through tooling-friendly annotations. By default, types from Java APIs used in Kotlin are recognized as platform types for which null-checks are relaxed. Kotlin’s support for JSR 305 annotations combined with nullability annotations provide null-safety for the related Spring API in Kotlin.
The JSR 305 checks can be configured by adding the -Xjsr305
compiler flag with the following options: -Xjsr305={strict|warn|ignore}
.
The default behavior is the same as -Xjsr305=warn
.
The strict
value is required to have null-safety taken in account in Kotlin types inferred from Spring API but should be used with the knowledge that Spring API nullability declaration could evolve even between minor releases and more checks may be added in the future).
Generic type arguments, varargs and array elements nullability are not yet supported. See SPR-15942 for up-to-date information. Also be aware that Spring Boot’s own API is not yet annotated. |
10.3. Kotlin API
10.3.1. runApplication
Spring Boot provides an idiomatic way to run an application with runApplication<MyApplication>(*args)
as shown in the following example:
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args)
}
This is a drop-in replacement for SpringApplication.run(MyApplication::class.java, *args)
.
It also allows customization of the application as shown in the following example:
runApplication<MyApplication>(*args) {
setBannerMode(OFF)
}
10.3.2. Extensions
Kotlin extensions provide the ability to extend existing classes with additional functionality. The Spring Boot Kotlin API makes use of these extensions to add new Kotlin specific conveniences to existing APIs.
TestRestTemplate
extensions, similar to those provided by Spring Framework for RestOperations
in Spring Framework, are provided.
Among other things, the extensions make it possible to take advantage of Kotlin reified type parameters.
10.4. Dependency management
In order to avoid mixing different versions of Kotlin dependencies on the classpath, Spring Boot imports the Kotlin BOM.
With Maven, the Kotlin version can be customized by setting the kotlin.version
property and plugin management is provided for kotlin-maven-plugin
.
With Gradle, the Spring Boot plugin automatically aligns the kotlin.version
with the version of the Kotlin plugin.
Spring Boot also manages the version of Coroutines dependencies by importing the Kotlin Coroutines BOM.
The version can be customized by setting the kotlin-coroutines.version
property.
org.jetbrains.kotlinx:kotlinx-coroutines-reactor dependency is provided by default if one bootstraps a Kotlin project with at least one reactive dependency on start.spring.io.
|
10.5. @ConfigurationProperties
@ConfigurationProperties
when used in combination with @ConstructorBinding
supports classes with immutable val
properties as shown in the following example:
@ConstructorBinding
@ConfigurationProperties("example.kotlin")
data class KotlinExampleProperties(
val name: String,
val description: String,
val myService: MyService) {
data class MyService(
val apiToken: String,
val uri: URI
)
}
To generate your own metadata using the annotation processor, kapt should be configured with the spring-boot-configuration-processor dependency.
Note that some features (such as detecting the default value or deprecated items) are not working due to limitations in the model kapt provides.
|
10.6. Testing
While it is possible to use JUnit 4 to test Kotlin code, JUnit 5 is provided by default and is recommended.
JUnit 5 enables a test class to be instantiated once and reused for all of the class’s tests.
This makes it possible to use @BeforeAll
and @AfterAll
annotations on non-static methods, which is a good fit for Kotlin.
To mock Kotlin classes, MockK is recommended.
If you need the MockK
equivalent of the Mockito specific @MockBean
and @SpyBean
annotations, you can use SpringMockK which provides similar @MockkBean
and @SpykBean
annotations.
10.7. Resources
10.7.1. Further reading
-
Kotlin Slack (with a dedicated #spring channel)
-
Tutorial: building web applications with Spring Boot and Kotlin
-
A Geospatial Messenger with Kotlin, Spring Boot and PostgreSQL
10.7.2. Examples
-
spring-boot-kotlin-demo: regular Spring Boot + Spring Data JPA project
-
mixit: Spring Boot 2 + WebFlux + Reactive Spring Data MongoDB
-
spring-kotlin-fullstack: WebFlux Kotlin fullstack example with Kotlin2js for frontend instead of JavaScript or TypeScript
-
spring-petclinic-kotlin: Kotlin version of the Spring PetClinic Sample Application
-
spring-kotlin-deepdive: a step by step migration for Boot 1.0 + Java to Boot 2.0 + Kotlin
-
spring-boot-coroutines-demo: Coroutines sample project
11. What to Read Next
If you want to learn more about any of the classes discussed in this section, see the Spring Boot API documentation or you can browse the source code directly. If you have specific questions, see the how-to section.
If you are comfortable with Spring Boot’s core features, you can continue on and read about production-ready features.