Java convert ArrayList to string and back to ArrayList?

Question

I wanted to save an ArrayList to SharedPreferences so I need to turn it into a string and back, this is what I am doing:

// Save to shared preferences
SharedPreferences sharedPref = this.getPreferences(Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = this.getPreferences(Activity.MODE_PRIVATE).edit();
editor.putString("myAppsArr", myAppsArr.toString());
editor.commit();

I can retrieve it with String arrayString = sharedPref.getString("yourKey", null); but I don't know how to convert arrayString back into an ArrayList. How can it be done?

My array looks something like:

[item1,item2,item3]

Dhruv Gairola · Accepted Answer · 2013-01-13 23:57:41Z

35

+50

You have 2 choices :

Manually parse the string and recreate the arraylist. This would be pretty tedious.

Use a JSON library like Google's Gson library to store and retrieve objects as JSON strings. This is a lightweight library, well regarded and popular. It would be an ideal solution in your case with minimal work required. e.g.,

// How to store JSON string
Gson gson = new Gson();
// This can be any object. Does not have to be an arraylist.
String json = gson.toJson(myAppsArr);

// How to retrieve your Java object back from the string
Gson gson = new Gson();
DataObject obj = gson.fromJson(arrayString, ArrayList.class);

edited Jan 13, 2013 at 23:57

answered Jan 13, 2013 at 23:48

Dhruv Gairola

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3 Comments

lisovaccaro Over a year ago

I changed the array elements to strings, I'm sure it must be a lot easier now.

Dhruv Gairola Over a year ago

It doesn't matter. With Gson, you can convert any java object to a string and then convert it back. So even if you have an arraylist of custom objects, there's no problem.

Shanika Ediriweera Over a year ago

Does it work for ArrayList<SomeCustomObject> with gson.fromJson(arrayString, ArrayList.class)?

Mykhailo Gaidai · Accepted Answer · 2013-01-14 00:19:21Z

3

Try this

ArrayList<String> array = Arrays.asList(arrayString.split(","))

This will work if comma is used as separator and none of the items have it.

answered Jan 14, 2013 at 0:19

Mykhailo Gaidai

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Comments

John Hascall · Accepted Answer · 2016-01-06 17:14:34Z

2

The page http://mjiayou.com/2015/07/22/exception-gson-internal-cannot-be-cast-to/ contains the following:

Type     type  = new TypeToken<List<T>>(){}.getType();
List<T>  list  = gson.fromJson(jsonString, type)

perhaps it will be helpful.

edited Jan 6, 2016 at 17:14

John Hascall

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answered Jan 6, 2016 at 13:29

user5752479

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Comments

Bhoomika Prajapati · Accepted Answer · 2019-01-09 06:57:28Z

2

      //arraylist convert into String using Gson 
      Gson gson = new Gson();
      String data = gson.toJson(myArrayList);
      Log.e(TAG, "json:" + gson);

      //String to ArrayList

      Gson gson = new Gson();
      arrayList=gson.fromJson(data, new TypeToken<List<Friends>>()
      {}.getType());

edited Jan 9, 2019 at 6:57

answered Jun 11, 2018 at 10:21

Bhoomika Prajapati

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Comments

lisovaccaro · Accepted Answer · 2013-01-15 21:55:20Z

1

I ended up using:

ArrayList<String> appList = new ArrayList<String>(Arrays.asList(appsString.split("\\s*,\\s*")));

This doesn't work for all array types though. This option differs from:

ArrayList<String> array = Arrays.asList(arrayString.split(","));

on that the second option creates an inmutable array.

answered Jan 15, 2013 at 21:55

lisovaccaro

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Comments

Quick learner · Accepted Answer · 2018-10-09 08:00:39Z

0

Update to Dhruv Gairola's answer for Kotlin

val gson = Gson();
val jsonString = gson.toJson(arrayList)

answered Oct 9, 2018 at 8:00

Quick learner

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