ANdroid Serialization causes ConcurrentModificationException. How can I avoid this?

Question

On serialization my object which is a custom class, holding various ArrayLists, every so often I get a Concurrent Mod Exception. Clearly one or more of the arraylists is throwing this. But I don't know where, or how to fix it. Implementing an iterator would be my first idea, but how to go about doing that for serialization?

This is my serialization code:enter code here

 try{
    ByteArrayOutputStream bos = new ByteArrayOutputStream(); 

    try { 
          ObjectOutput out = new ObjectOutputStream(bos); 
          out.writeObject(TGame);

          // Get the bytes of the serialized object 
          byte[] buf = bos.toByteArray(); 

          File sdCard = Environment.getExternalStorageDirectory();
          File dir = new File (sdCard.getAbsolutePath() + "/game_folder");
          dir.mkdirs();
          File file = new File(dir, "serializationtest");


          FileOutputStream fos = new FileOutputStream(file);
              //this.openFileOutput(filename, Context.MODE_PRIVATE);
          fos.write(buf);
          fos.close(); 
        } catch(IOException ioe) { 
          Log.e("serializeObject", "error", ioe); 


        }catch(StackOverflowError e){
            //do something
        }

        File f =this.getDir(filename, 0);
        Log.v("FILE SAVED",f.getName());    
    }catch(ConcurrentModificationException e){
        //do something          
    }
}

Answer 1

While Java api is serializing the object ( here inner array list), if at the same time some other thread Structurally Modifies ArrayList then you get a Concurrent Mod Exception.

One solution is Locking Mechanism ensuring that only one thread accesses that object at a Time. Another simple solution is that the object that is to be written, create a shallow copy of that object and serialize that copy. This way even if original ArrayList changes, shallow copy will have not effect and will work fine. e.g.

class Test {
 int a;
 string b;
 ArrayList<String> c;
 Test(Test t){
  this.a=t.a;
  this.b=t.b;
  this.c=new ArrayList<String>(t.c);
 }
}
FileOutputStream fos = new FileOutputStream(file);
//write a copy of original object
      fos.write(new Test(t));

}