Spring Boot includes an additional set of tools that can make the application
development experience a little more pleasant. The spring-boot-devtools
module can be
included in any project to provide additional development-time features. To include
devtools support, add the module dependency to your build, as shown in the following
listings for Maven and Gradle:
Maven.
<dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-devtools</artifactId> <optional>true</optional> </dependency> </dependencies>
Gradle.
dependencies {
compile("org.springframework.boot:spring-boot-devtools")
}
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Developer tools are automatically disabled when running a fully packaged
application. If your application is launched from |
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Repackaged archives do not contain devtools by default. If you want to use a
certain remote devtools feature, you need to disable the
|
Several of the libraries supported by Spring Boot use caches to improve performance. For example, template engines cache compiled templates to avoid repeatedly parsing template files. Also, Spring MVC can add HTTP caching headers to responses when serving static resources.
While caching is very beneficial in production, it can be counter-productive during development, preventing you from seeing the changes you just made in your application. For this reason, spring-boot-devtools disables the caching options by default.
Cache options are usually configured by settings in your application.properties
file.
For example, Thymeleaf offers the spring.thymeleaf.cache
property. Rather than needing
to set these properties manually, the spring-boot-devtools
module automatically applies
sensible development-time configuration.
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For a complete list of the properties that are applied by the devtools, see DevToolsPropertyDefaultsPostProcessor. |
Applications that use spring-boot-devtools
automatically restart whenever files on the
classpath change. This can be a useful feature when working in an IDE, as it gives a very
fast feedback loop for code changes. By default, any entry on the classpath that points
to a folder is monitored for changes. Note that certain resources, such as static assets
and view templates, do not need to restart the
application.
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As long as forking is enabled, you can also start your application by using the supported build plugins (Maven and Gradle), since DevTools needs an isolated application classloader to operate properly. By default, Gradle and Maven do that when they detect DevTools on the classpath. |
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Automatic restart works very well when used with LiveReload. See the LiveReload section for details. If you use JRebel, automatic restarts are disabled in favor of dynamic class reloading. Other devtools features (such as LiveReload and property overrides) can still be used. |
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DevTools relies on the application context’s shutdown hook to close it during a
restart. It does not work correctly if you have disabled the shutdown hook
( |
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When deciding if an entry on the classpath should trigger a restart when it
changes, DevTools automatically ignores projects named |
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DevTools needs to customize the |
By default, each time your application restarts, a report showing the condition evaluation delta is logged. The report shows the changes to your application’s auto-configuration as you make changes such as adding or removing beans and setting configuration properties.
To disable the logging of the report, set the following property:
spring.devtools.restart.log-condition-evaluation-delta=false
Certain resources do not necessarily need to trigger a restart when they are changed. For
example, Thymeleaf templates can be edited in-place. By default, changing resources
in /META-INF/maven
, /META-INF/resources
, /resources
, /static
, /public
, or
/templates
does not trigger a restart but does trigger a
live reload. If you want to customize these
exclusions, you can use the spring.devtools.restart.exclude
property. For example, to
exclude only /static
and /public
you would set the following property:
spring.devtools.restart.exclude=static/**,public/**
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If you want to keep those defaults and add additional exclusions, use the
|
You may want your application to be restarted or reloaded when you make changes to files
that are not on the classpath. To do so, use the
spring.devtools.restart.additional-paths
property to configure additional paths to
watch for changes. You can use the spring.devtools.restart.exclude
property
described earlier to control whether changes
beneath the additional paths trigger a full restart or a
live reload.
If you do not want to use the restart feature, you can disable it by using the
spring.devtools.restart.enabled
property. In most cases, you can set this property in
your application.properties
(doing so still initializes the restart classloader, but it
does not watch for file changes).
If you need to completely disable restart support (for example, because it does not work
with a specific library), you need to set the spring.devtools.restart.enabled
System
property to false
before calling SpringApplication.run(…)
, as shown in the
following example:
public static void main(String[] args) { System.setProperty("spring.devtools.restart.enabled", "false"); SpringApplication.run(MyApp.class, args); }
If you work with an IDE that continuously compiles changed files, you might prefer to trigger restarts only at specific times. To do so, you can use a “trigger file”, which is a special file that must be modified when you want to actually trigger a restart check. Changing the file only triggers the check and the restart only occurs if Devtools has detected it has to do something. The trigger file can be updated manually or with an IDE plugin.
To use a trigger file, set the spring.devtools.restart.trigger-file
property to the
path of your trigger file.
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You might want to set |
As described earlier in the Restart vs Reload section, restart functionality is implemented by using two classloaders. For most applications, this approach works well. However, it can sometimes cause classloading issues.
By default, any open project in your IDE is loaded with the “restart” classloader, and
any regular .jar
file is loaded with the “base” classloader. If you work on a
multi-module project, and not every module is imported into your IDE, you may need to
customize things. To do so, you can create a META-INF/spring-devtools.properties
file.
The spring-devtools.properties
file can contain properties prefixed with
restart.exclude
and restart.include
. The include
elements are items that should be
pulled up into the “restart” classloader, and the exclude
elements are items that
should be pushed down into the “base” classloader. The value of the property is a regex
pattern that is applied to the classpath, as shown in the following example:
restart.exclude.companycommonlibs=/mycorp-common-[\\w-]+\.jar restart.include.projectcommon=/mycorp-myproj-[\\w-]+\.jar
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All property keys must be unique. As long as a property starts with
|
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All |
Restart functionality does not work well with objects that are deserialized by using a
standard ObjectInputStream
. If you need to deserialize data, you may need to use
Spring’s ConfigurableObjectInputStream
in combination with
Thread.currentThread().getContextClassLoader()
.
Unfortunately, several third-party libraries deserialize without considering the context classloader. If you find such a problem, you need to request a fix with the original authors.
The spring-boot-devtools
module includes an embedded LiveReload server that can be used
to trigger a browser refresh when a resource is changed. LiveReload browser extensions
are freely available for Chrome, Firefox and Safari from
livereload.com.
If you do not want to start the LiveReload server when your application runs, you can set
the spring.devtools.livereload.enabled
property to false
.
![]() | Note |
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You can only run one LiveReload server at a time. Before starting your application, ensure that no other LiveReload servers are running. If you start multiple applications from your IDE, only the first has LiveReload support. |
You can configure global devtools settings by adding a file named
.spring-boot-devtools.properties
to your $HOME
folder (note that the filename starts
with “.”). Any properties added to this file apply to all Spring Boot applications on
your machine that use devtools. For example, to configure restart to always use a
trigger file, you would add the following
property:
~/.spring-boot-devtools.properties.
spring.devtools.reload.trigger-file=.reloadtrigger
The Spring Boot developer tools are not limited to local development. You can also
use several features when running applications remotely. Remote support is opt-in. To
enable it, you need to make sure that devtools
is included in the repackaged archive,
as shown in the following listing:
<build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <excludeDevtools>false</excludeDevtools> </configuration> </plugin> </plugins> </build>
Then you need to set a spring.devtools.remote.secret
property, as shown in the
following example:
spring.devtools.remote.secret=mysecret
![]() | Warning |
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Enabling |
Remote devtools support is provided in two parts: a server-side endpoint that accepts
connections and a client application that you run in your IDE. The server component is
automatically enabled when the spring.devtools.remote.secret
property is set. The
client component must be launched manually.
The remote client application is designed to be run from within your IDE. You need to run
org.springframework.boot.devtools.RemoteSpringApplication
with the same classpath as
the remote project that you connect to. The application’s single required argument is the
remote URL to which it connects.
For example, if you are using Eclipse or STS and you have a project named my-app
that
you have deployed to Cloud Foundry, you would do the following:
Run Configurations…
from the Run
menu.Java Application
“launch configuration”.my-app
project.org.springframework.boot.devtools.RemoteSpringApplication
as the main class.https://myapp.cfapps.io
to the Program arguments
(or whatever your remote
URL is).A running remote client might resemble the following listing:
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ ___ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | | _ \___ _ __ ___| |_ ___ \ \ \ \ \\/ ___)| |_)| | | | | || (_| []::::::[] / -_) ' \/ _ \ _/ -_) ) ) ) ) ' |____| .__|_| |_|_| |_\__, | |_|_\___|_|_|_\___/\__\___|/ / / / =========|_|==============|___/===================================/_/_/_/ :: Spring Boot Remote :: 2.0.0.RELEASE 2015-06-10 18:25:06.632 INFO 14938 --- [ main] o.s.b.devtools.RemoteSpringApplication : Starting RemoteSpringApplication on pwmbp with PID 14938 (/Users/pwebb/projects/spring-boot/code/spring-boot-devtools/target/classes started by pwebb in /Users/pwebb/projects/spring-boot/code/spring-boot-samples/spring-boot-sample-devtools) 2015-06-10 18:25:06.671 INFO 14938 --- [ main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2a17b7b6: startup date [Wed Jun 10 18:25:06 PDT 2015]; root of context hierarchy 2015-06-10 18:25:07.043 WARN 14938 --- [ main] o.s.b.d.r.c.RemoteClientConfiguration : The connection to http://localhost:8080 is insecure. You should use a URL starting with 'https://'. 2015-06-10 18:25:07.074 INFO 14938 --- [ main] o.s.b.d.a.OptionalLiveReloadServer : LiveReload server is running on port 35729 2015-06-10 18:25:07.130 INFO 14938 --- [ main] o.s.b.devtools.RemoteSpringApplication : Started RemoteSpringApplication in 0.74 seconds (JVM running for 1.105)
![]() | Note |
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Because the remote client is using the same classpath as the real application it
can directly read application properties. This is how the |
![]() | Tip |
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It is always advisable to use |
![]() | Tip |
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If you need to use a proxy to access the remote application, configure the
|
The remote client monitors your application classpath for changes in the same way as the local restart. Any updated resource is pushed to the remote application and (if required) triggers a restart. This can be helpful if you iterate on a feature that uses a cloud service that you do not have locally. Generally, remote updates and restarts are much quicker than a full rebuild and deploy cycle.
![]() | Note |
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Files are only monitored when the remote client is running. If you change a file before starting the remote client, it is not pushed to the remote server. |