Use GSON library for that. Here is the sample code

List<String> foo = new ArrayList<String>();
foo.add("A");
foo.add("B");
foo.add("C");

String json = new Gson().toJson(foo );

Here is the maven dependency for Gson

<dependencies>
    <!--  Gson: Java to Json conversion -->
    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.2.2</version>
        <scope>compile</scope>
    </dependency>
</dependencies>

Or you can directly download jar from here and put it in your class path

http://code.google.com/p/google-gson/downloads/detail?name=gson-1.0.jar&can=4&q=

To send Json to client you can use spring or in simple servlet add this code

response.getWriter().write(json);

JSONArray att = new JSONArray(YourList);

If I read the JSONArray constructors correctly, you can build them from any Collection (arrayList is a subclass of Collection) like so:

ArrayList<String> list = new ArrayList<String>();
list.add("foo");
list.add("baar");
JSONArray jsArray = new JSONArray(list);

References:

• jsonarray constructor: http://developer.android.com/reference/org/json/JSONArray.html#JSONArray%28java.util.Collection%29
• collection: http://developer.android.com/reference/java/util/Collection.html

Using gson it is much simpler. Use following code snippet:

 // create a new Gson instance
 Gson gson = new Gson();
 // convert your list to json
 String jsonCartList = gson.toJson(cartList);
 // print your generated json
 System.out.println("jsonCartList: " + jsonCartList);

Converting back from JSON string to your Java object

 // Converts JSON string into a List of Product object
 Type type = new TypeToken<List<Product>>(){}.getType();
 List<Product> prodList = gson.fromJson(jsonCartList, type);

 // print your List<Product>
 System.out.println("prodList: " + prodList);

To convert ArrayList to Json, just download Open Source json utility from: http://json.org/java/ or Jar file from here

And just do:

JSONArray jsonAraay = new JSONArray(your_array_list);

That's it

Note: You should have setter/getter in your POJO/MODEL class to convert arraylist to json

You should convert your list to a JSON Array, and just use its toString() function:

JSONArray myArray = new JSONArray(jsonObjlist);

// ...
String arrayToJson = myArray.toString(2);

The int parameter specifies the indent factor to use for formatting.