How can I create a Spring 5 component index?

Question

Spring Framework 5 apparently contains support for a "component index" which lives in META-INF/spring.components and can be used to avoid the need for class-path scanning, and thus, I assume, improve a webapps' startup time.

See:

• The "what's new in spring 5" mention
• The jira issue under which the support was developed
• Some examples of what the spring.components format seems to be from the change implementing it

How can I create such a component index for an existing web app I plan to upgrade to Spring 5?

(Ideally it would get generated automatically at build time with Maven I imagine, but any other workable approaches would at least give me a starting point to work from)

Answer 1

Spring 5 Has added a new feature to improve startup performance of large applications.

it creates a list of component candidates at compilation time.

In this mode, all modules of the application must use this mechanism as, when the ApplicationContext detects such index, it will automatically use it rather than scanning the classpath.

To generate the index, we just need to add below dependency to each module

Maven:

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-indexer</artifactId>
        <version>5.0.3.RELEASE</version>
        <optional>true</optional>
    </dependency>
</dependencies>

Gradle

dependencies {
    compileOnly("org.springframework:spring-context-indexer:5.0.3.RELEASE")
}

This process will generate a META-INF/spring.components file that is going to be included in the jar.

Reference : 1.10.9. Generating an index of candidate components

Answer 2

The META-INF/spring.components files are generated by an annotation processor library called spring-context-indexer. If you add this library as "annotation processor path" to the maven-compiler-plugin, the files will be generated automatically at build time:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-compiler-plugin</artifactId>
  <configuration>
    <annotationProcessorPaths>
      <path>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-indexer</artifactId>
        <version>5.0.6.RELEASE</version>
      </path>
    </annotationProcessorPaths>
    ...
  </configuration>
</plugin>

This setup requires maven-compiler-plugin version 3.5 or greater.

See also: https://maven.apache.org/plugins/maven-compiler-plugin/compile-mojo.html#annotationProcessorPaths