This plugin will automatically build your java or android project with retrolambda, giving you lambda goodness on java 6 or 7. It relies on the wonderful retrolambda by Esko Luontola.

Note: The minimum android gradle plugin is 1.0.0.

1. Download jdk8.

2. Add the following to your build.gradle

   buildscript {
      repositories {
         mavenCentral()
      }
   
      dependencies {
         classpath 'me.tatarka:gradle-retrolambda:2.5.0'
      }
   }
   
   // Required because retrolambda is on maven central
   repositories {
      mavenCentral()
   }
   
   apply plugin: 'com.android.application' //or apply plugin: 'java'
   apply plugin: 'me.tatarka.retrolambda'

3. There is no step three!

The plugin will compile the source code with java8 and then replace the class files with the output of retrolambda.

Configuration is entirely optional, the plugin will by default pick up the JAVA6_HOME/JAVA7_HOME/JAVA8_HOME environment variables. It's also smart enough to figure out what version of java you are running gradle with. For example, if you have java8 set as your default, you only need to define JAVA6_HOME/JAVA7_HOME. If you need to though, you can add a block like the following to configure the plugin:

retrolambda {
  jdk System.getenv("JAVA8_HOME")
  oldJdk System.getenv("JAVA6_HOME")
  javaVersion JavaVersion.VERSION_1_6
  jvmArgs '-arg1', '-arg2'
}

• jdk Set the path to the java 8 jdk. The default is found using the environment variable JAVA8_HOME. If you a running gradle with java 6 or 7, you must have either JAVA8_HOME or this property set.
• oldJdk Sets the path to the java 6 or 7 jdk. The default is found using the environment variable JAVA6_HOME/JAVA7_HOME. If you are running gradle with java 8 and wish to run unit tests, you must have either JAVA6_HOME/JAVA7_HOME or this property set. This is so the tests can be run with the correct java version.
• javaVersion Set the java version to compile to. The default is 6. Only 6 or 7 are accepted.
• include 'Debug', 'Release' Sets which sets/variants to run through retrolambda. The default is all of them.
• exclude 'Test' Sets which sets/variants to not run through retrolambda. Only one of either include or exclude should be defined.
• jvmArgs Add additional jvm args when running retrolambda.

The default version of retrolambda used is 'net.orfjackal.retrolambda:retrolambda:1.6.0'. If you want to use a different one, you can configure it in your dependencies.

dependencies {
  // Latest one on maven central
  retrolambdaConfig 'net.orfjackal.retrolambda:retrolambda:1.+'
  // Or a local version
  // retrolambdaConfig files('libs/retrolambda.jar')
}

Add these lines to your build.gradle to inform the IDE of the language level.

android {
  compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
  }
}

This plugin is fully compatible with progurad (since v2.4.0). In your progurad file, add

-dontwarn java.lang.invoke.*

Version 5.0.77 contains bytecode that is incompatible with retrolambda. To work around this issue, you can either use an earlier version like 4.4.52 or add -noverify to the jvm args. See orfjackal/retrolambda#25 for more information.

retrolambda {
  jvmArgs '-noverify'
}

For some reason only known to the gods, when using Android Studio's sdk manager, there is no android-L directory sdk directory. Instead, it happily builds using the android-20 directory instead. To work around this, you can symlink the android-L directory to point to android-20. See #36.

This is because android-apt modifies the javaCompile task and this plugin replaces it. Since v2.4.1 this is fixed, you just need to ensure you apply this plugin before android-apt.

There were two hurdles to overcome when compiling for android. The gradle android plugin forces a compile targeting java 6 and uses a custom bootclasspath that doesn't include necessary java8 files. To overcome this, the plugin:

1. Overrides -source and -target with 8.
2. Extracts the necessary files out of the java runtime (rt.jar), and patches android.jar with them.
3. Sets -bootclasspath to point to the patched android.jar

All updates have moved to the CHANGELOG.