Maven - Use JDK 7 to Compile for JVM 5

Question

I've been trying to get this to work for a while now but no luck yet.

I want to run with JAVA_HOME pointing to JDK7 but I want to compile a project for JVM 5. I've read through documentation, I've found similar posts on SO, but none of them seem to work in my setup.

I first tried with setting just target and source but I got an error:

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

[ClassName] is not abstract and does not override abstract method getParentLogger() in CommonDataSource

As far as I understood that class was updated in JDK 7 and the extra method that's throwing the error was just added. I need to use the runtime of JDK 5 that has the old implementation and everything should work fine. So I do this:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <verbose>true</verbose>
        <source>1.5</source>
        <target>1.5</target>
        <compilerArguments>
            <bootclasspath>${env.JAVA5_HOME}/jre/lib/rt.jar</bootclasspath>
        </compilerArguments>
    </configuration>
</plugin>

I have JAVA5_HOME set correctly on my system, I can see it loading the correct classes in the log, but I hit another error:

[loading ZipFileIndexFileObject[c:\Program Files\Java\jdk1.5.0_22\jre\lib\rt.jar(*.class)]]
...
...
[ClassName] error: package javax.crypto does not exist

Which is fair enough, since I didn't include jce.jar (cryptography classes) in the bootclasspath. There is a thing that puzzles me, though. Even though the bootclasspath contains only the Java 5 runtime, I have a lot of libraries from JRE7 in the classpath. They are not specified anywhere.

[search path for class files: c:\Program Files (x86)\Java\jdk1.5.0_22\jre\lib\rt.jar,c:\Program Files\Java\jdk1.7.0_02\jre\lib\ext\dnsns.jar,c:\Program Files\Java\jdk1.7.0_02\jre\lib\ext\localedata.jar,c:\Program Files\Java\jdk1.7.0_02\jre\lib\ext\sunec.jar,c:\Program Files\Java\jdk1.7.0_02\jre\lib\ext\sunjce_provider.jar,c:\Program Files\Java\jdk1.7.0_02\jre\lib\ext\sunmscapi.jar,c:\Program Files\Java\jdk1.7.0_02\jre\lib\ext\zipfs.jar, ...]

If I try and add jce.jar (from JRE5), I get back to the first error:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <verbose>true</verbose>
        <source>1.5</source>
        <target>1.5</target>
        <compilerArguments>
            <bootclasspath>${env.JAVA5_HOME}/jre/lib/rt.jar${path.separator}${env.JAVA5_HOME}/jre/lib/jce.jar</bootclasspath>
        </compilerArguments>
    </configuration>
</plugin>

The type [ClassName] must implement the inherited abstract method CommonDataSource.getParentLogger()

I also see no trace of rt.jar being loaded, but I don't get a java.lang not found error, so there are some classes being loaded on the classpath.

I'll fix it temporarily by making a batch script that overwrites JAVA_HOME before building and sets it back afterwards, but I really want this done the right way. This doesn't seem as such an extreme use-case. :)

What am I doing wrong here?

Answer 1

This answer is targeted at the title of the question, not to the specific problems of the question in detail.

I ended up using this solution in my project, which allows me to use the custom bootstrap classpath selectively, by activating a maven profile. I strongly recommend using a profile for this, because otherwise it makes the build fail for anyone that does not have the environment variable set (very bad, especially for an open source project). I only activate this profile in my IDE for the "Clean & Build" action.

    <profile>
        <id>compileWithJava5</id>
        <!--
            NOTE
            Make sure to set the environment variable JAVA5_HOME
            to your JDK 1.5 HOME when using this profile.
        -->
        <properties>
            <java.5.home>${env.JAVA5_HOME}</java.5.home>
            <java.5.libs>${java.5.home}/jre/lib</java.5.libs>
            <java.5.bootclasspath>${java.5.libs}/rt.jar${path.separator}${java.5.libs}/jce.jar</java.5.bootclasspath>
        </properties>
        <build>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <configuration>
                        <source>1.5</source>
                        <target>1.5</target>
                        <compilerArguments>
                            <bootclasspath>${java.5.bootclasspath}</bootclasspath>
                        </compilerArguments>
                    </configuration>
                </plugin>
            </plugins>
        </build>
    </profile>