How to enforce a java compiler version with gradle?

Question

In all of my projects, I use gradle and specify the following:

sourceCompatibility = "1.7"; // for example
targetCompatibility = "1.7"; // defaults to sourceCompatibility

Now, I have three different versions of the JDK installed, from 1.6 to 1.8. In order to switch from one version to another, I source shell files to change PATH, JAVA_HOME and even JDK_HOME.

By accident it can happen that I use the wrong JDK version and I don't want that... Is there a possibility to check that the compiler version is equal to targetCompatibility before attempting any compilation task?

Answer 1

Answer to self, and thanks to @JBNizet for providing the initial solution...

The solution is indeed to use JavaVersion, and it happens that both sourceCompatibility and targetCompatibility accept a JavaVersion as an argument...

Therefore the build file has become this:

def javaVersion = JavaVersion.VERSION_1_7;
sourceCompatibility = javaVersion;
targetCompatibility = javaVersion; // defaults to sourceCompatibility

And then the task:

task enforceVersion << {
    def foundVersion = JavaVersion.current();
    if (foundVersion != javaVersion) 
        throw new IllegalStateException("Wrong Java version; required is "
            + javaVersion + ", but found " + foundVersion);
}

compileJava.dependsOn(enforceVersion);

And it works:

$ ./gradlew clean compileJava
:clean UP-TO-DATE
:enforceVersion FAILED

FAILURE: Build failed with an exception.

* Where:
Build file '/home/fge/src/perso/grappa-tracer-backport/build.gradle' line: 55

* What went wrong:
Execution failed for task ':enforceVersion'.
> Wrong Java version; required is 1.7, but found 1.8