Include java.lang.invoke classes in bootstrap classpath.

build.gradle

@@ -24,3 +24,27 @@ buildscript {
 		classpath files('libs/gradle-witness.jar')
 	}
 }
+
+// If a Java 6 JRE is available, check we're not using any Java 7 or 8 APIs
+ext.useJava6StandardLibrary = { task ->
+	def home = System.env.JAVA_6_HOME;
+	if (home != null && !home.isEmpty()) {
+		println "Setting Java 6 bootstrap classpath for ${task.name}"
+		task.dependsOn createJavaLangInvokeJar
+		task.options.bootstrapClasspath = files(
+				"${project.rootDir}/build/invoke.jar",
+				"${home}/jre/lib/rt.jar",
+				"${home}/jre/lib/jsse.jar"
+		)
+	}
+}
+
+// Create a jar containing the java.lang.invoke classes for the Java 6 bootstrap classpath
+task createJavaLangInvokeJar(type: Zip) {
+	archiveName 'invoke.jar'
+	destinationDir file("${project.rootDir}/build")
+	from zipTree("${System.getProperty('java.home')}/lib/rt.jar").matching {
+		include 'java/lang/invoke/*'
+	}
+	include '**/*'
+}