Using Eclipse Java Compiler (ecj) in maven builds

Question

Eclipse uses it's own compiler (ECJ) to compile Java code. Debugging a program compiled with Eclipse is easier, because simple code changes can be applied instantly (by the hot code replacement).

Maven on the other hand uses (by default) oracle JDK, that generates different byte code preventing hot code replacement in a Eclipse debug session.

So I would like to use Eclipse ECJ compiler with my maven build, if I plan to debug the program. A convenient way for me would be a "ecj" profile:

• Compile release

  $ mvn package
  

• Compile snapshot with enabled hot code replacement

  $ mvn -P ecj package
  

Also the profile activation can be specified in settings.xml or even Eclipse project properties.

My questions are:

1. Is this the right way to go?
2. How this can be configured?
3. Can maven toolchain be used for this?

Answer 1

It is possible to change the default javac compiler that is used by the maven-compiler-plugin. The Eclipse compiler is bundled in the artifact plexus-compiler-eclipse and it is declared by setting eclipse to the compilerId attribute of the maven-compiler-plugin.

If you want to activate this change for a custom profile, you could have the following configuration:

<profile>
  <id>ecj</id>
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.6.0</version>
        <configuration>
          <compilerId>eclipse</compilerId>
        </configuration>
        <dependencies>
          <dependency>
            <groupId>org.codehaus.plexus</groupId>
            <artifactId>plexus-compiler-eclipse</artifactId>
            <version>2.8.1</version>
          </dependency>
        </dependencies>
      </plugin>
    </plugins>
  </build>
</profile>

The plugin is maintained in the plexus-compiler GitHub repository. Version 2.8.1 uses 3.11.1.v20150902-1521 of JDT, although you could use your own version by adding a dependency on org.eclipse.tycho:org.eclipse.jdt.core after the Plexus Compiler dependency.