Support Java 8 language features in Java modules.

bramble-api/build.gradle

 apply plugin: 'java'
-sourceCompatibility = 1.6
-targetCompatibility = 1.6
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
 
 apply plugin: 'witness'
 
@@ -35,3 +35,13 @@ task jarTest(type: Jar, dependsOn: testClasses) {
 artifacts {
 	testOutput jarTest
 }
+
+// If a Java 6 JRE is available, check we're not using any Java 7 or 8 APIs
+tasks.withType(JavaCompile) {
+	doFirst {
+		def home = System.env.JAVA_6_HOME;
+		if (home != null && !home.isEmpty()) {
+			options.bootstrapClasspath = files("${home}/jre/lib/rt.jar", "${home}/jre/lib/jsse.jar")
+		}
+	}
+}

bramble-core/build.gradle

 apply plugin: 'java'
-sourceCompatibility = 1.6
-targetCompatibility = 1.6
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
 
 apply plugin: 'net.ltgt.apt'
 apply plugin: 'idea'
@@ -38,3 +38,13 @@ task jarTest(type: Jar, dependsOn: testClasses) {
 artifacts {
 	testOutput jarTest
 }
+
+// If a Java 6 JRE is available, check we're not using any Java 7 or 8 APIs
+tasks.withType(JavaCompile) {
+	doFirst {
+		def home = System.env.JAVA_6_HOME;
+		if (home != null && !home.isEmpty()) {
+			options.bootstrapClasspath = files("${home}/jre/lib/rt.jar", "${home}/jre/lib/jsse.jar")
+		}
+	}
+}

bramble-j2se/build.gradle

 apply plugin: 'java'
-sourceCompatibility = 1.7
-targetCompatibility = 1.7
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
 
 apply plugin: 'net.ltgt.apt'
 apply plugin: 'idea'

briar-api/build.gradle

 apply plugin: 'java'
-sourceCompatibility = 1.6
-targetCompatibility = 1.6
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
 
 dependencies {
 	compile project(path: ':bramble-api', configuration: 'default')
 }
+
+// If a Java 6 JRE is available, check we're not using any Java 7 or 8 APIs
+tasks.withType(JavaCompile) {
+	doFirst {
+		def home = System.env.JAVA_6_HOME;
+		if (home != null && !home.isEmpty()) {
+			options.bootstrapClasspath = files("${home}/jre/lib/rt.jar", "${home}/jre/lib/jsse.jar")
+		}
+	}
+}

briar-core/build.gradle

 apply plugin: 'java'
-sourceCompatibility = 1.6
-targetCompatibility = 1.6
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
 
 apply plugin: 'net.ltgt.apt'
 apply plugin: 'idea'
@@ -33,3 +33,13 @@ dependencyVerification {
 			'com.squareup.okio:okio:734269c3ebc5090e3b23566db558f421f0b4027277c79ad5d176b8ec168bb850',
 	]
 }
+
+// If a Java 6 JRE is available, check we're not using any Java 7 or 8 APIs
+tasks.withType(JavaCompile) {
+	doFirst {
+		def home = System.env.JAVA_6_HOME;
+		if (home != null && !home.isEmpty()) {
+			options.bootstrapClasspath = files("${home}/jre/lib/rt.jar", "${home}/jre/lib/jsse.jar")
+		}
+	}
+}

settings.gradle

-include ':bramble-api', ':bramble-android'
+include ':bramble-api'
 include ':bramble-core'
+include ':bramble-android'
 include ':bramble-j2se'
 include ':briar-api'
 include ':briar-core'