Does Maven really honor the <source> tag in the compiler plugin?

Question

I work on a Java program that should be compatibe with Java 5. I had @Override annotations on implemented interface methods which is allowed in Java 6, but not in 5. I use a Java 6 SDK. Eclipse correctly gives error messages on the @Override when I set it to 5.0 compliance. My Maven build, however, runs without even a warning, using the following settings in my POM:

    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <configuration>
        <source>1.5</source>
        <target>1.5</target>
      </configuration>
    </plugin>

Am I correct in expecting that this should actually make the build fail? Why doesn't it, and is there something I can do?

Answer 1

This is actually a JDK problem, not a Maven problem. The @Override annotation is not failing with a -source 1.5 flag to to a 1.6 javac. Go ahead and try it. The only way to make it fail, is, unfortunately, to use a 1.5 javac.

Sorry, HTH.

EDIT
I ran into this problem myself, and I also wondered if it's actually looking at the setting in the pom. Turning on debug output (-X I believe, was a while ago) will print the javac command line to the standard output, and you'll see that it is indeed using the -source 1.5 parameter.

Answer 2

As roe's answer says you need to use a 1.5 compiler because the JDK isn't doing its job quite right. It's worth pointing out that you can avoid messing about with paths etc. by tweaking the maven-compiler-plugin configuration to use a specific compiler:

<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
      <verbose>true</verbose>
      <fork>true</fork>
      <executable>${JAVA_1_5_HOME}/bin/javac</executable>
      <compilerVersion>1.5</compilerVersion>
    </configuration>
  </plugin>
  ...
</plugins>

You can then specify the path to the compiler in your project or settings.xml

<properties>
  <JAVA_1_5_HOME>/path/to/1.5jdk</JAVA_1_5_HOME>
</properties>