Below code should work for your case.

List<Customer> customerList = CustomerDB.selectAll();

Gson gson = new Gson();
JsonElement element = gson.toJsonTree(customerList, new TypeToken<List<Customer>>() {}.getType());

if (! element.isJsonArray() ) {
// fail appropriately
    throw new SomeException();
}

JsonArray jsonArray = element.getAsJsonArray();

Heck, use List interface to collect values before converting it JSON Tree.

This way is worked for me:

Convert all list to String.

String element = gson.toJson(
                    groupsList,
           new TypeToken<ArrayList<GroupItem>>() {}.getType());

Create JSONArray from String:

    JSONArray list = new JSONArray(element);

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

There is a sample from google gson documentation on how to actually convert the list to json string:

Type listType = new TypeToken<List<String>>() {}.getType();
 List<String> target = new LinkedList<String>();
 target.add("blah");

 Gson gson = new Gson();
 String json = gson.toJson(target, listType);
 List<String> target2 = gson.fromJson(json, listType);

You need to set the type of list in toJson method and pass the list object to convert it to json string or vice versa.

Here's a comprehensive example on how to use Gson with a list of objects. This should demonstrate exactly how to convert to/from Json, how to reference lists, etc.

Test.java:

import com.google.gson.Gson;
import java.util.List;
import java.util.ArrayList;
import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Type;


public class Test {

  public static void main (String[] args) {

    // Initialize a list of type DataObject
    List<DataObject> objList = new ArrayList<DataObject>();
    objList.add(new DataObject(0, "zero"));
    objList.add(new DataObject(1, "one"));
    objList.add(new DataObject(2, "two"));

    // Convert the object to a JSON string
    String json = new Gson().toJson(objList);
    System.out.println(json);

    // Now convert the JSON string back to your java object
    Type type = new TypeToken<List<DataObject>>(){}.getType();
    List<DataObject> inpList = new Gson().fromJson(json, type);
    for (int i=0;i<inpList.size();i++) {
      DataObject x = inpList.get(i);
      System.out.println(x);
    }

  }


  private static class DataObject {
    private int a;
    private String b;

    public DataObject(int a, String b) {
      this.a = a;
      this.b = b;
    }

    public String toString() {
      return "a = " +a+ ", b = " +b;
    }
  }

}

To compile it:

javac -cp "gson-2.1.jar:." Test.java

And finally to run it:

java -cp "gson-2.1.jar:." Test

Note that if you're using Windows, you'll have to switch : with ; in the previous two commands.

After you run it, you should see the following output:

[{"a":0,"b":"zero"},{"a":1,"b":"one"},{"a":2,"b":"two"}]
a = 0, b = zero
a = 1, b = one
a = 2, b = two

Keep in mind that this is only a command line program to demonstrate how it works, but the same principles apply within the Android environment (referencing jar libs, etc.)

Definitely the easiest way to do that is using Gson's default parsing function fromJson().

There is an implementation of this function suitable for when you need to deserialize into any ParameterizedType (e.g., any List), which is fromJson(JsonElement json, Type typeOfT).

In your case, you just need to get the Type of a List<String> and then parse the JSON array into that Type, like this:

import java.lang.reflect.Type;
import com.google.gson.reflect.TypeToken;

JsonElement yourJson = mapping.get("servers");
Type listType = new TypeToken<List<String>>() {}.getType();

List<String> yourList = new Gson().fromJson(yourJson, listType);

In your case yourJson is a JsonElement, but it could also be a String, any Reader or a JsonReader.

You may want to take a look at Gson API documentation.

you can use the below code to convert json to corresponding list of objects

TypeToken<List<Animal>> token = new TypeToken<List<Animal>>() {};
List<Animal> animals = gson.fromJson(data, token.getType());

You can convert your JsonArray or json string to ArrayList<OBJECT> using Gson library as below

ArrayList<OBJECT> yourArray = new Gson().fromJson(jsonString, new TypeToken<List<OBJECT>>(){}.getType());

//or

ArrayList<OBJECT> yourArray = new Gson().fromJson(myjsonarray.toString(), new TypeToken<List<OBJECT>>(){}.getType());

Also while converting your ArrayList<OBJECT> to JsonArray, no need to convert it to string and back to JsonArray

 JsonArray myjsonarray = new Gson().toJsonTree(MyArrayList<OBJECT>).getAsJsonArray();

Refer Gson API documentation for more details. Hope this will be helpful.