How to add java compiler options when compiling with Android Gradle Plugin?

Add this to build.gradle file:

android { // <---
   tasks.withType(JavaCompile) {
      configure(options) {
         options.encoding = 'UTF-8'
         options.debug = true
         options.failOnError = true
         options.warnings = true
         options.compilerArgs << '-Xlint:deprecation' << '-Xlint:unchecked'
   }
}

I tried the solution posed by @Konrad Jamrozik but it didn't work with my project due to flavours in my project.

Given that we're just turning on additional warnings, not something that's significantly changing how the compiler operates, I don't see it being an issue that it will be added to both release and debug builds. As such, this answer has a cleaner method that works with flavours: How to add -Xlint:unchecked to my Android Gradle based project?

In my case, adding this to the build.gradle file of the affected module:

gradle.projectsEvaluated {
   tasks.withType(JavaCompile) {
        options.compilerArgs << "-Xlint:unchecked" << "-Xlint:deprecation"
    }
}

I found the following solution based on Gradle Plugin User Guide on Manipulating Tasks and Gradle DSL doc about JavaCompile:

Add to build.gradle:

preBuild {
    doFirst {
        JavaCompile jc = android.applicationVariants.find { it.name == 'debug' }.javaCompile
        jc.options.compilerArgs = ["-Xlint:unchecked"]
    }
}

The application variants are null during Gradle's configuration phase and the required JavaCompile task also doesn't exist, thus I do the modification in the execution phase instead.