How do I serialize an object and save it to a file in Android?


Question

Say I have some simple class and once it's instantiated as an object I want to be able to serialize its contents to a file, and retrieve it by loading that file at some later time... I'm not sure where to start here, what do I need to do to serialize this object to a file?

public class SimpleClass {
   public string name;
   public int id;
   public void save() {
       /* wtf do I do here? */
   }
   public static SimpleClass load(String file) {
       /* what about here? */
   }
}

This is probably the easiest question in the world, because this is a really simple task in .NET, but in Android I'm pretty new so I'm completely lost.

1
124
4/26/2015 5:49:30 PM

Accepted Answer

Saving (w/o exception handling code):

FileOutputStream fos = context.openFileOutput(fileName, Context.MODE_PRIVATE);
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(this);
os.close();
fos.close();

Loading (w/o exception handling code):

FileInputStream fis = context.openFileInput(fileName);
ObjectInputStream is = new ObjectInputStream(fis);
SimpleClass simpleClass = (SimpleClass) is.readObject();
is.close();
fis.close();
241
4/27/2015 3:00:18 PM

I've tried this 2 options (read/write), with plain objects, array of objects (150 objects), Map:

Option1:

FileOutputStream fos = context.openFileOutput(fileName, Context.MODE_PRIVATE);
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(this);
os.close();

Option2:

SharedPreferences mPrefs=app.getSharedPreferences(app.getApplicationInfo().name, Context.MODE_PRIVATE);
SharedPreferences.Editor ed=mPrefs.edit();
Gson gson = new Gson(); 
ed.putString("myObjectKey", gson.toJson(objectToSave));
ed.commit();

Option 2 is twice quicker than option 1

The option 2 inconvenience is that you have to make specific code for read:

Gson gson = new Gson();
JsonParser parser=new JsonParser();
//object arr example
JsonArray arr=parser.parse(mPrefs.getString("myArrKey", null)).getAsJsonArray();
events=new Event[arr.size()];
int i=0;
for (JsonElement jsonElement : arr)
    events[i++]=gson.fromJson(jsonElement, Event.class);
//Object example
pagination=gson.fromJson(parser.parse(jsonPagination).getAsJsonObject(), Pagination.class);

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