JAVA_HOME gets mangled by Maven

Question

I'm retrofitting bunch of existing Java projects with unified Maven build. Since each project is mature and has established Ant based build all I'm using maven-antrun-plugin to execute existing build.xml as follows:

        <plugin>
            <artifactId>maven-antrun-plugin</artifactId>
            <executions>
                <execution>
                    <phase>compile</phase>
                    <configuration>
                        <tasks>
                            <ant antfile="build.xml" target="compile" />
                        </tasks>
                    </configuration>
                    <goals>
                        <goal>run</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>

When I run mvn compile build fails with this message:

[INFO] An Ant BuildException has occured: The following error occurred 
       while executing  this line:
build.xml:175: Unable to find a javac compiler;
com.sun.tools.javac.Main is not on the classpath.
Perhaps JAVA_HOME does not point to the JDK.
It is currently set to "C:\Java\jdk1.6.0_13\jre"

What puzzles me is

1. I have JAVA_HOME=C:\Java\jdk1.6.0_13 as part of my environment setup and when mvn.bat is executed that is exactly value I'm getting, however as you see in the error message it comes up as C:\Java\jdk1.6.0_13\jre
2. If I run ant compile everything compiles just fine

Does it mean that perhaps maven-antrun-plugin does something like set JAVA_HOME=%JAVA_HOME%\jre? I searched my batch/build files I can't find where that change occurs

Answer 1

Thats the down side of external links in an accepted answer. Codehaus shut down and thus the solution is gone. For reference here's the content behind the link - you basically only need to copy the <dependencies>...</dependencies> block to your antrun plugin...

The maven-antrun-plugin runs ant with JAVA_HOME set to the jre subdirectory of the JDK, even if the JAVA_HOME for the overall run is a JDK. There is documentation elsewhere about how to create a dependency at the project level for the JDK's tools.jar, but this does not help out antrun, which is a plugin. The following profile does the job. The '..' in the path hauls up past the 'jre' directory to the lib directory.

<profiles>
      <profile>
          <id>tools.jar</id>
          <build>
            <plugins>
            <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-antrun-plugin</artifactId>
              <dependencies>
                <dependency>
                  <groupId>com.sun</groupId>
                  <artifactId>tools</artifactId>
                  <version>1.5.0</version>
                  <scope>system</scope>
                  <systemPath>${java.home}/../lib/tools.jar</systemPath>
                </dependency>
              </dependencies>
            </plugin>
            </plugins>
          </build>
      </profile>

Answer 2

I was able to fix this by putting the following property definition in my ant build.xml file:

<property name="build.compiler" value="extJavac"/>