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Make classloader customization easier to discover

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See gh-29438
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Andreas Ahlenstorf 2022-01-16 16:40:21 +01:00 committed by Stephane Nicoll
parent 697c30346d
commit 96f48db2ab
1 changed files with 16 additions and 6 deletions
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22
spring-boot-project/spring-boot-docs/src/docs/asciidoc/using/devtools.adoc
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@ -24,6 +24,8 @@ To include devtools support, add the module dependency to your build, as shown i
}
----
CAUTION: Devtools might cause classloading issues, in particular in multi-module projects. <<using#using.devtools.diagnosing-classloading-issues>> explains how to diagnose and solve them.
NOTE: Developer tools are automatically disabled when running a fully packaged application.
If your application is launched from `java -jar` or if it is started from a special classloader, then it is considered a "`production application`".
You can control this behavior by using the `spring.devtools.restart.enabled` system property.
@ -40,6 +42,17 @@ When using the Gradle plugin, {spring-boot-gradle-plugin-docs}#packaging-executa
[[using.devtools.diagnosing-classloading-issues]]
=== Diagnosing Classloading Issues
As described in the <<using#using.devtools.restart.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, in particular in multi-module projects.
To diagnose whether the classloading issues are indeed caused by devtools and its two classloaders, <<using#using.devtools.restart.disable,try disabling restart>>. If this solves your problems, <<using#using.devtools.restart.customizing-the-classload,customize the restart classloader>> to include your entire project.
[[using.devtools.property-defaults]]
=== Property Defaults
Several of the libraries supported by Spring Boot use caches to improve performance.
@ -214,14 +227,11 @@ For IntelliJ IDEA, you can follow the https://www.jetbrains.com/help/idea/spring
[[using.devtools.restart.customizing-the-classload]]
==== Customizing the Restart Classloader
As described earlier in the <<using-spring-boot-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.
As described earlier in the <<using-spring-boot-restart-vs-reload>> section, restart functionality is implemented by using two classloaders. If this causes issues, you might need to customize what gets loaded by which classloader.
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.
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. The same is true if you use `mvn spring-boot:run` or `gradle bootRun`: The project containing your `@SpringBootApplication` is loaded with the "`restart`" classloader, and everything else with the "`base`" classloader.
You can instruct Spring Boot to load parts of your project with a different classloader by creating 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: