print_hook.js

Java.perform(function() {
    ['java.lang.StringBuilder', 'java.lang.StringBuffer'].forEach(function(clazz, i) {
      console.log('[?] ' + i + ' = ' + clazz);
      var func = 'toString';
      Java.use(clazz)[func].implementation = function() {
        var ret = this[func]();
        if (ret.indexOf('') != -1) {
          // print stacktrace if return value contains specific string
          Java.perform(function() {
            var jAndroidLog = Java.use("android.util.Log"), jException = Java.use("java.lang.Exception");
            console.log( jAndroidLog.getStackTraceString( jException.$new() ) );
          }); 
        }   
        send('[' + i + '] ' + ret);
        return ret;
      }   
    }); 
  });