Writing Data Structures to files using FileOutputStream?

Question

I have an android application and want to store/retrieve to memory a data structure that I created on the onPause()/onResume() methods so that the data will persist between runs via FileOutputStream/FileInputStream, which is the standard practice for this.

So, how do I save a data structure to a file so that I can obtain it later (I've seen examples of doing it with Strings but not other objects)? Am I forced to create a getBytes() function for my data structure and the subsequent objects which it contains in addition to making constructors for all of these objects that creates them from byte arrays?

Edit: Ah, okay; so this is called serialization. Is the the following correct?

To write:

FileOutputStream fileOut = new FileOutputStream("filename");
ObjectOutputStream out = new ObjectOutputStream(fileOut);
out.writeObject(e);
out.close();
fileOut.close();

To read:

FileInputStream fileIn = new FileInputStream("filename");
ObjectInputStream in = new ObjectInputStream(fileIn);
e = (ObjectType) in.readObject();
in.close();
fileIn.close();

Edit2: Also, the data structure and contained objects (and sub-objects) should all implement Serializable. So for instance, if I had a BST of ArrayLists of Dogs then I would make the BST, ArrayList, and Dog classes all implement Serializable and then call the functions above.

Is all of this correct?

Answer 1

Look into the Serializable library here . This allows you to write a class directly down to a non-human readable file, then can be read back in the same way.

Answer 2

Its common to serialize your data with JSON or XML. Otherwise, you could look into google protocol buffers for a more densely packed data file.