Android - SharedPreferences with serializable object

Solution 1:

In short you cant, try serializing your object to a private file, it amounts to the same thing. sample class below:

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import android.app.Activity;
import android.content.Context;

/**
 *
 * Writes/reads an object to/from a private local file
 * 
 *
 */
public class LocalPersistence {


    /**
     * 
     * @param context
     * @param object
     * @param filename
     */
    public static void witeObjectToFile(Context context, Object object, String filename) {

        ObjectOutputStream objectOut = null;
        try {

            FileOutputStream fileOut = context.openFileOutput(filename, Activity.MODE_PRIVATE);
            objectOut = new ObjectOutputStream(fileOut);
            objectOut.writeObject(object);
            fileOut.getFD().sync();

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (objectOut != null) {
                try {
                    objectOut.close();
                } catch (IOException e) {
                    // do nowt
                }
            }
        }
    }


    /**
     * 
     * @param context
     * @param filename
     * @return
     */
    public static Object readObjectFromFile(Context context, String filename) {

        ObjectInputStream objectIn = null;
        Object object = null;
        try {

            FileInputStream fileIn = context.getApplicationContext().openFileInput(filename);
            objectIn = new ObjectInputStream(fileIn);
            object = objectIn.readObject();

        } catch (FileNotFoundException e) {
            // Do nothing
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } finally {
            if (objectIn != null) {
                try {
                    objectIn.close();
                } catch (IOException e) {
                    // do nowt
                }
            }
        }

        return object;
    }

}

Solution 2:

The accepted answer is misleading, we can store serializable object into SharedPreferences by using GSON. Read more about it at google-gson.

you can add GSON dependency in Gradle file with:

compile 'com.google.code.gson:gson:2.7'

Here the snippet:

First, create your usual sharedPreferences:

//Creating a shared preference
SharedPreferences  mPrefs = getPreferences(MODE_PRIVATE);

Saving from serializable object to preference:

 Editor prefsEditor = mPrefs.edit();
 Gson gson = new Gson();
 String json = gson.toJson(YourSerializableObject);
 prefsEditor.putString("SerializableObject", json);
 prefsEditor.commit();

Get serializable object from preference:

Gson gson = new Gson();
String json = mPrefs.getString("SerializableObject", "");
yourSerializableObject = gson.fromJson(json, YourSerializableObject.class);

Solution 3:

If you object is simple POJO you can convert object to JSON string and save it in shared preferences with putString().

Solution 4:

It is possible to do it without a file.

I'm serializing the information to base64 and like this I'm able to save it as a string in the preferences.

The following code is Serializing a serializable objec to base64 string and vice versa: import android.util.Base64;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;


public class ObjectSerializerHelper {
    static public String objectToString(Serializable object) {
        String encoded = null;
        try {
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
            objectOutputStream.writeObject(object);
            objectOutputStream.close();
            encoded = new String(Base64.encodeToString(byteArrayOutputStream.toByteArray(),0));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return encoded;
    }

    @SuppressWarnings("unchecked")
    static public Serializable stringToObject(String string){
        byte[] bytes = Base64.decode(string,0);
        Serializable object = null;
        try {
            ObjectInputStream objectInputStream = new ObjectInputStream( new ByteArrayInputStream(bytes) );
            object = (Serializable)objectInputStream.readObject();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (ClassCastException e) {
            e.printStackTrace();
        }
        return object;
    }

}