Tools: Idea Intellij, Android SDK, gradle;
Sometimes there are multiple projects in a root project, and one project would refer to other projects as dependencies, if more than one projects contain the same library, it will cause "Multiple dex files define" error when building release version. "exclude" instruction would help us solve this problem.
First, check out those modules which being mulitple include:
gradlew -q :%module%:dependencies
Then edit "build.gradle" file in your application module, exlude them. In my case, I get rid of v7, v4 and annotations from a library module named "memorize":
exclude group: 'com.android.support', module: 'appcompat-v7'
exclude group: 'com.android.support', module: 'support-v4'
exclude group: 'com.android.support', module: 'support-annotations'
exclude module: 'ActiveAndroid'