The SpringApplication
class provides a convenient way to bootstrap a Spring application
that will be started from a main()
method. In many situations you can just delegate to
the static SpringApplication.run
method:
public static void main(String[] args) { SpringApplication.run(MySpringConfiguration.class, args); }
When your application starts you should see something similar to the following:
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: v1.5.7.RELEASE 2013-07-31 00:08:16.117 INFO 56603 --- [ main] o.s.b.s.app.SampleApplication : Starting SampleApplication v0.1.0 on mycomputer with PID 56603 (/apps/myapp.jar started by pwebb) 2013-07-31 00:08:16.166 INFO 56603 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6e5a8246: startup date [Wed Jul 31 00:08:16 PDT 2013]; root of context hierarchy 2014-03-04 13:09:54.912 INFO 41370 --- [ main] .t.TomcatEmbeddedServletContainerFactory : Server initialized with port: 8080 2014-03-04 13:09:56.501 INFO 41370 --- [ main] o.s.b.s.app.SampleApplication : Started SampleApplication in 2.992 seconds (JVM running for 3.658)
By default INFO
logging messages will be shown, including some relevant startup details
such as the user that launched the application.
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:
*************************** APPLICATION FAILED TO START *************************** Description: Embedded servlet container failed to start. Port 8080 was already in use. Action: Identify and stop the process that's listening on port 8080 or configure this application to listen on another port.
![]() | Note |
---|---|
Spring Boot provides numerous |
If no failure analyzers are able to handle the exception, you can still display the full
auto-configuration 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.AutoConfigurationReportLoggingInitializer
.
For instance, if you are running your application using java -jar
you can enable the
debug
property as follows:
$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug
The banner that is printed on start up can be changed by adding a banner.txt
file
to your classpath, or by setting banner.location
to the location of such a file.
If the file has an unusual encoding you can set banner.charset
(default is UTF-8
).
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 a banner.image.location
property. Images will be
converted into an ASCII art representation and printed above any text banner.
Inside your banner.txt
file you can use any of the following placeholders:
Table 23.1. Banner variables
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 |
![]() | Tip |
---|---|
The |
You can also use the spring.main.banner-mode
property to determine if the banner has
to be printed on System.out
(console
), using the configured logger (log
) or not
at all (off
).
The printed banner will be registered as a singleton bean under the name
springBootBanner
.
![]() | Note |
---|---|
YAML maps spring: main: banner-mode: "off" |
If the SpringApplication
defaults aren’t to your taste you can instead create a local
instance and customize it. For example, to turn off the banner you would write:
public static void main(String[] args) { SpringApplication app = new SpringApplication(MySpringConfiguration.class); app.setBannerMode(Banner.Mode.OFF); app.run(args); }
![]() | Note |
---|---|
The constructor arguments passed to |
It is also possible to configure the SpringApplication
using an application.properties
file. See Chapter 24, Externalized Configuration for details.
For a complete list of the configuration options, see the
SpringApplication
Javadoc.
If you need to build an ApplicationContext
hierarchy (multiple contexts with a
parent/child relationship), or if you just prefer using a ‘fluent’ builder API, you
can use the SpringApplicationBuilder
.
The SpringApplicationBuilder
allows you to chain together multiple method calls, and
includes parent
and child
methods that allow you to create a hierarchy.
For example:
new SpringApplicationBuilder() .sources(Parent.class) .child(Application.class) .bannerMode(Banner.Mode.OFF) .run(args);
![]() | Note |
---|---|
There are some restrictions when creating an |
In addition to the usual Spring Framework events, such as
ContextRefreshedEvent
,
a SpringApplication
sends some additional application events.
![]() | Note |
---|---|
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:
ApplicationStartingEvent
is sent at the start of a run, but before any
processing except the registration of listeners and initializers.ApplicationEnvironmentPreparedEvent
is sent when the Environment
to be used in
the context is known, but before the context is created.ApplicationPreparedEvent
is sent just before the refresh is started, but after bean
definitions have been loaded.ApplicationReadyEvent
is sent after the refresh and any related callbacks have
been processed to indicate the application is ready to service requests.ApplicationFailedEvent
is sent if there is an exception on startup.![]() | Tip |
---|---|
You often won’t need to use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks. |
A SpringApplication
will attempt to create the right type of ApplicationContext
on
your behalf. By default, an AnnotationConfigApplicationContext
or
AnnotationConfigEmbeddedWebApplicationContext
will be used, depending on whether you
are developing a web application or not.
The algorithm used to determine a ‘web environment’ is fairly simplistic (based on the
presence of a few classes). You can use setWebEnvironment(boolean webEnvironment)
if
you need to override the default.
It is also possible to take complete control of the ApplicationContext
type that will
be used by calling setApplicationContextClass(…)
.
![]() | Tip |
---|---|
It is often desirable to call |
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:
import org.springframework.boot.* import org.springframework.beans.factory.annotation.* import org.springframework.stereotype.* @Component public class MyBean { @Autowired public MyBean(ApplicationArguments args) { boolean debug = args.containsOption("debug"); List<String> files = args.getNonOptionArgs(); // if run with "--debug logfile.txt" debug=true, files=["logfile.txt"] } }
![]() | Tip |
---|---|
Spring Boot will also register a |
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 will be called just before
SpringApplication.run(…)
completes.
The CommandLineRunner
interfaces provides access to application arguments as a simple
string array, whereas the ApplicationRunner
uses the ApplicationArguments
interface
discussed above.
import org.springframework.boot.* import org.springframework.stereotype.* @Component public class MyBean implements CommandLineRunner { public void run(String... args) { // Do something... } }
You can additionally implement the org.springframework.core.Ordered
interface or use the
org.springframework.core.annotation.Order
annotation if several CommandLineRunner
or
ApplicationRunner
beans are defined that must be called in a specific order.
Each SpringApplication
will register a shutdown hook with the JVM to ensure that the
ApplicationContext
is closed 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.
@SpringBootApplication public class ExitCodeApplication { @Bean public ExitCodeGenerator exitCodeGenerator() { return new ExitCodeGenerator() { @Override public int getExitCode() { return 42; } }; } public static void main(String[] args) { System.exit(SpringApplication .exit(SpringApplication.run(ExitCodeApplication.class, args))); } }
Also, the ExitCodeGenerator
interface may be implemented by exceptions. When such an
exception is encountered, Spring Boot will return the exit code provided by the
implemented getExitCode()
method.
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 could also be useful for any service wrapper implementation.
![]() | Tip |
---|---|
If you want to know on which HTTP port the application is running, get the property
with key |
![]() | Note |
---|---|
Take care when enabling this feature as the MBean exposes a method to shutdown the application. |