How to save HashMap to Shared Preferences?

How can I save a HashMap Object into Shared Preferences in Android?

Solution 1:

I use Gson to convert HashMap to String and then save it to SharedPrefs

private void hashmaptest()
{
    //create test hashmap
    HashMap<String, String> testHashMap = new HashMap<String, String>();
    testHashMap.put("key1", "value1");
    testHashMap.put("key2", "value2");

    //convert to string using gson
    Gson gson = new Gson();
    String hashMapString = gson.toJson(testHashMap);

    //save in shared prefs
    SharedPreferences prefs = getSharedPreferences("test", MODE_PRIVATE);
    prefs.edit().putString("hashString", hashMapString).apply();

    //get from shared prefs
    String storedHashMapString = prefs.getString("hashString", "oopsDintWork");
    java.lang.reflect.Type type = new TypeToken<HashMap<String, String>>(){}.getType();
    HashMap<String, String> testHashMap2 = gson.fromJson(storedHashMapString, type);

    //use values
    String toastString = testHashMap2.get("key1") + " | " + testHashMap2.get("key2");
    Toast.makeText(this, toastString, Toast.LENGTH_LONG).show();
}

Solution 2:

I would not recommend writing complex objects into SharedPreference. Instead I would use ObjectOutputStream to write it to the internal memory.

File file = new File(getDir("data", MODE_PRIVATE), "map");    
ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream(file));
outputStream.writeObject(map);
outputStream.flush();
outputStream.close();

Solution 3:

private void saveMap(Map<String,Boolean> inputMap) {
    SharedPreferences pSharedPref = getApplicationContext().getSharedPreferences("MyVariables", Context.MODE_PRIVATE);
    if (pSharedPref != null){
        JSONObject jsonObject = new JSONObject(inputMap);
        String jsonString = jsonObject.toString();
        pSharedPref.edit()
            .remove("My_map")
            .putString("My_map", jsonString)
            .apply();
    }
}

private Map<String,Boolean> loadMap() {
    Map<String,Boolean> outputMap = new HashMap<>();
    SharedPreferences pSharedPref = getApplicationContext().getSharedPreferences("MyVariables", Context.MODE_PRIVATE);
    try {
        if (pSharedPref != null) {
            String jsonString = pSharedPref.getString("My_map", (new JSONObject()).toString());
            if (jsonString != null) {
                JSONObject jsonObject = new JSONObject(jsonString);
                Iterator<String> keysItr = jsonObject.keys();
                while (keysItr.hasNext()) {
                    String key = keysItr.next();
                    Boolean value = jsonObject.getBoolean(key); 
                    outputMap.put(key, value);
                }
            }
        }
    } catch (JSONException e){
        e.printStackTrace();
    }
    return outputMap;
}

Solution 4:

Map<String, String> aMap = new HashMap<String, String>();
aMap.put("key1", "val1");
aMap.put("key2", "val2");
aMap.put("Key3", "val3");

SharedPreferences keyValues = getContext().getSharedPreferences("Your_Shared_Prefs"), Context.MODE_PRIVATE);
SharedPreferences.Editor keyValuesEditor = keyValues.edit();

for (String s : aMap.keySet()) {
    keyValuesEditor.putString(s, aMap.get(s));
}

keyValuesEditor.commit();

Solution 5:

As a spin off of Vinoj John Hosan's answer, I modified the answer to allow for more generic insertions, based on the key of the data, instead of a single key like "My_map".

In my implementation, MyApp is my Application override class, and MyApp.getInstance() acts to return the context.

public static final String USERDATA = "MyVariables";

private static void saveMap(String key, Map<String,String> inputMap){
    SharedPreferences pSharedPref = MyApp.getInstance().getSharedPreferences(USERDATA, Context.MODE_PRIVATE);
    if (pSharedPref != null){
        JSONObject jsonObject = new JSONObject(inputMap);
        String jsonString = jsonObject.toString();
        SharedPreferences.Editor editor = pSharedPref.edit();
        editor.remove(key).commit();
        editor.putString(key, jsonString);
        editor.commit();
    }
}

private static Map<String,String> loadMap(String key){
    Map<String,String> outputMap = new HashMap<String,String>();
    SharedPreferences pSharedPref = MyApp.getInstance().getSharedPreferences(USERDATA, Context.MODE_PRIVATE);
    try{
        if (pSharedPref != null){
            String jsonString = pSharedPref.getString(key, (new JSONObject()).toString());
            JSONObject jsonObject = new JSONObject(jsonString);
            Iterator<String> keysItr = jsonObject.keys();
            while(keysItr.hasNext()) {
                String k = keysItr.next();
                String v = (String) jsonObject.get(k);
                outputMap.put(k,v);
            }
        }
    }catch(Exception e){
        e.printStackTrace();
    }
    return outputMap;
}