How to set Gradle `options.bootClasspath` in an os independent manner?

Question

Because my Java sources and targets must be JRE 1.6 compatible, I need to set options.bootClasspath to a path that contains the 1.6 versions of rt.jar and jce.jar. It must build on both Windows and Unix (Linux/Solaris). What is the proper way to do this? I now use the following approach in my top-level build.gradle, it works, but it seems far from elegant, especially the os-dependent separator : or ;:

import org.apache.tools.ant.taskdefs.condition.Os

subprojects {
  apply plugin: 'java'

  compileJava {
    sourceCompatibility = 1.6
    targetCompatibility = 1.6
    def java6_home = System.getenv("JAVA_HOME_6")
    def java6_lib = "C:/localdata/Program Files (x86)/Java/jdk1.6.0_45/jre/lib/"

    if (java6_home != null) {
      java6_lib = java6_home + "/jre/lib/"
    }

    def sep = ':'
    if (Os.isFamily(Os.FAMILY_WINDOWS)) {
      sep = ';'
    }
    options.bootClasspath = java6_lib + "rt.jar" + sep + java6_lib + "jce.jar"
  }
}

Answer 1

I am using the following code (assuming the JDK6_HOME points to the root of the JDK 1.6 installation):

tasks.withType(JavaCompile) {
    doFirst {
        if (sourceCompatibility == '1.6' && System.env.JDK6_HOME != null) {
            options.fork = true
            options.bootClasspath = "$System.env.JDK6_HOME/jre/lib/rt.jar"
            options.bootClasspath += "$File.pathSeparator$System.env.JDK6_HOME/jre/lib/jsse.jar"
            // use the line above as an example to add jce.jar 
            // and other specific JDK jars
        }
    }
}

This approach automatically detects the presence of the environment variable and automatically sets the bootClasspath for all modules that declare sourceCompatibility as 1.6.

The options.fork = true is required when you use bootClasspath.

Answer 2

The accepted answer can work, but if you're using some classes outside java.lang (e.g. javax.crypto.*) you may find you'll get various ClassNotFoundExceptionException's being raised as more JAR files need to be added to the bootClasspath.

To avoid this, I use the following which has the following advantages;

• The options are only set if required
• All the JAR files are added to the bootClasspath
• The extensionDirs is also set (see http://docs.oracle.com/javase/7/docs/technotes/tools/windows/javac.html#extdirs-option)

.

tasks.withType(JavaCompile) {
    doFirst {
        if (JavaVersion.toVersion(sourceCompatibility) == JavaVersion.VERSION_1_6
            && JavaVersion.current() != JavaVersion.VERSION_1_6
            && System.env.JDK6_HOME != null) {
            options.fork = true
            options.bootClasspath = fileTree(include: ['*.jar'], dir: "$System.env.JDK6_HOME/jre/lib/").join(File.pathSeparator)
            options.extensionDirs = "$System.env.JDK6_HOME/jre/lib/ext/"
        }
    }
}

Answer 3

Since Gradle 4.3 you can use CompileOptions.bootstrapClasspath instead to remove the need for an OS-dependent separator.