How to compile a rosjava package offline?

edit

Thanks. That gave me an idea: always try to download URL, but keep a copy just in case. In build.gradle I changed this:

buildscript { 
  apply from: "https://github.com/rosjava/rosjava_bootstrap/raw/indigo/buildscript.gradle"  
}

To this:

buildscript {
    def f = new File("buildscript.gradle") 
    try{ 
    new URL("https://github.com/rosjava/rosjava_bootstrap/raw/indigo/buildscript.gradle").withInputStream{ i -> f.withOutputStream{ it << i }}    
    } catch (all) { 
      //do nothing, keep cached script 
    }  
    apply from: "buildscript.gradle"  
}

So I keep a local copy, but if available, downloads from internet.