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Does anyone have a clean example of a maven project preprocessing class annotations at compile time with subsequent generation of classes to be compiled in the same compilation process?

Does anyone have a step-by-step procedure to implement such a project?

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Jérôme Verstrynge
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3 Answers3

25

After navigating a lot in existing documentation on the net, I came up with the following:

What needs to be clarified:

  • In order to process annotations on a given project P, you first need an annotation processor compiled in a separate library S. P should have a dependency on S.
  • Implementing annotation processing in Java 5 is absolutely not the same thing as in Java 6.
  • Java 5 relies on a separate execution of apt. The corresponding tutorials here and here help understanding the basics of annotation processing and implementation in Java 5. Good reading for newbies.
  • Implementing annotation processing in Java 5 with Maven is tricky. One needs to add a local dependency to tools.jar to access the API described in these tutorials. Not clean. Some third-party plugins calling the apt are available, but not well documented.
  • Those using Java 6 should not jump-start implementing their processors according to the above tutorials.

Annotation Processing in Java 6 with Maven

  • A new package has been delivered in Java 6 to process annotations: the Pluggable Annotation Processing.
  • To implement a processor, create a separate Maven project. The above tutorial or this one explains how to proceed. This is our library S.
  • Then, create your project P and add a Maven dependency on S.
  • There is currently an issue with the maven-compiler-plugin, but a workaround is available here. Use it to compile your generated code as part of existing annotated code.

...and code generation

  • A great Java code generation library called CodeModel is available from Maven central. A good tutorial is available here. The javax annotation processing package offers some tools to generate output too.
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Jérôme Verstrynge
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    There is a lot of good stuff in this answer. But one thing is NOT true: you can do it in one maven pass. Here is an example that also includes an annotation processor using JCodeModel: https://github.com/jjYBdx4IL/example-maven-project-setups/tree/master/compile-time-annotation-processing – user1050755 Mar 03 '16 at 11:17
  • @user1050755 Thanks for a great suggestion. One question: why did you use that JCodeModel and not the official one? https://github.com/javaee/jaxb-codemodel – Don Rhummy Jul 31 '17 at 13:08
4

maven-processor-plugin can do that...

https://code.google.com/p/maven-annotation-plugin/

Example from documentation:

<build> <plugins>
  <!-- Run annotation processors on src/main/java sources -->
  <plugin>
    <groupId>org.bsc.maven</groupId>
    <artifactId>maven-processor-plugin</artifactId>
    <executions>
      <execution>
        <id>process</id>
        <goals>
          <goal>process</goal>
        </goals>
        <phase>generate-sources</phase>
      </execution>
    </executions>
  </plugin>
  <!-- Disable annotation processors during normal compilation -->
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
      <compilerArgument>-proc:none</compilerArgument>
    </configuration>
  </plugin>
</plugins> </build>
Dežo
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0

The Maven-Antlr-Plugin exactly does this. It generates Java classes from a grammar and the compile plugin compiles the generated classes. May it might be usefull the maven-annotation-plugin

khmarbaise
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    Thanks, but honestly I think maven-antlr-plugin is overkill. Moreover, the site does not provide a complete example explaining how to solve the issue I raise. I am thinking more about something along the AnnotationProcessor.The maven-annotation-plugin looks interesting, but it is work-in-progress with incomplete documentation. Not helpful. – Jérôme Verstrynge Aug 06 '11 at 16:09
  • I don't think he was advocating **using** the antlr plugin directly, but looking at its source to see how it does what it does. –  Aug 07 '11 at 17:49