How to have an extra compile goal in POM, which uses a different Java version?

Question

I have a library which is used via inline taglets. It's intended to be used by other libraries, for inserting example code into their JavaDoc.

The library is done, and, hallelujah, as of yesterday, it's now on Maven Central.

I'm now implementing this library into another project for the first time. That project compiles its code with java.version 1.5. But the taglet library requires 1.7. Not just for running javadoc.exe, but also for compiling optional "taglet customizer" classes.

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UPDATE: These customizer classes are created by each developer--the person using the taglet library in their library. The customizer classes (which are completely optional--they're needed only for advanced features, and you can get away with creating none) are required to be compiled before executing javadoc.exe.

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So it needs the following goals:

1. Compile the main library classes (requires Java 1.5) (mvn compile)
2. Compile the customizers (requires Java 1.7) (mvn compilecodelet?)
3. Run javadoc.exe (Java 1.7) (`mvn docs'?)

mvn install would therefore call these three goals in order.

I'm new to Maven, and would appreciate some advice on how to do this. This is what I've found out so far:

Here's the project's current compile goal:

<properties>
    <java.version>1.5</java.version>
</properties>

<plugin>
   <artifactId>maven-compiler-plugin</artifactId>
   <version>2.3.2</version>
   <configuration>
      <encoding>UTF-8</encoding>
      <source>${java.version}</source>
      <target>${java.version}</target>
   </configuration>
</plugin>

It seems the JDK for this project should be upgraded to 1.7, with the main classes compiled with the <source> and <target> flags set to 1.5, and the taglet-customizers compiled with those flags set to 1.7.

Some references:

• maven-compiler-plugin overview
• Compiling Sources Using A Different JDK, but I believe the only JDK hi

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How can I set up this extra compilecodelet goal, and set the whole project up so it can handle both JDK versions? And so that mvn install (and whatever other "master" goals) also call this new sub-goal in the proper sequence?

As I said, I'm new to Maven, and although I'm starting to understand bits and pieces, but I don't know how to put this all together yet.

Thank you for helping.

Answer 1

I share the misgivings of the others who commented on your question, doing what you ask seems risky and error-prone to me. It might be better to put the codelet extension classes in a separate project, build them with source & target of 1.7, and add a dependency on the codelet extension jar in the library POM's javadoc plugin configuration.

However if that is not possible, I would try something like this. It is untested but should give you the idea.

Assuming this directory structure:

basedir
  src
    main
      java
         regularLibCodePackage
         codeletExtensionPackage

<properties>
  <java.version>1.5</java.version>
  <!-- sets encoding for the whole Maven build -->
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

<plugin>
  <artifactId>maven-compiler-plugin</artifactId>
  <version>2.3.2</version>  <!--consider using latest plugin version -->
  <configuration>
    <!-- applies to all executions unless overridden by an execution -->
    <source>${java.version}</source>
    <target>${java.version}</target>
  </configuration>
  <executions>
    <execution>
      <id>default-compile</id>
      <configuration>
        <excludes>
          <!-- Not sure exactly what the path should be here, the docs aren't 
               clear. Maybe it should be an absolute path, e.g. 
               ${project.basedir}/src/main/java/codeletExtensionPackage?
               When you figure it out let me know and I'll edit the response. -->
          <exclude>codeletExtensionPackage</exclude>
        </excludes>
      </configuration>
    </execution>
    <execution>
      <id>codelet-compile</id>
      <phase>compile</phase>
      <goals>
        <goal>compile</goal>
      </goals>
      <configuration>
        <source>1.7</source>
        <target>1.7</target>
        <excludes>
          <!-- See note above about what to put here -->
          <exclude>regularLibCodePackage</exclude>
        </excludes>
      </configuration>
    </execution>
  </executions>
</plugin>

Do you need to keep the 1.7 classes out of the final jar? In other words, are the additional classes just required for running the Javadoc plugin? If the answer is 'yes' then you will also need to adjust the default jar plugin execution. (And if the answer is yes, this is another reason to put the codelet classes in a separate project!)

<plugin>
  <artifactId>maven-jar-plugin</artifactId>
  <version>2.5</version>  <!--consider using latest plugin version -->
  <executions>
    <execution>
      <id>default-jar</id>
      <configuration>
        <excludes>
          <exclude>codeletExtensionPackage</exclude>
        </excludes>
      </configuration>
    </execution>
  </executions>
</plugin>

I used excludes in the compiler and jar plugin configs, there is a companion includes block as well. I leave it to you to figure out the working config, this should get you started.