No-args constructor for class XXX does not exist - java

I am new to Android development. Here, I am making a GET call like this -
protected String doInBackground(String... params) {
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
nameValuePairs.add(new BasicNameValuePair("email", "guest#example.com"));
JSONHttpClient jsonHttpClient = new JSONHttpClient();
ProductDetail[] products = jsonHttpClient.Get(ServiceUrl.PRODUCT, nameValuePairs, ProductDetail[].class);
return null;
}
This is the GET call in JSONHttpClient file -
public <T> T Get(String url, List<NameValuePair> params, final Class<T> objectClass) {
DefaultHttpClient defaultHttpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
httpGet.setHeader("Accept", "application/json");
httpGet.setHeader("Accept-Encoding", "gzip");
httpGet.setHeader("Authorization", "Bearer <code>");
HttpResponse httpResponse = defaultHttpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
if (httpEntity != null) {
InputStream inputStream = httpEntity.getContent();
Header contentEncoding = httpResponse.getFirstHeader("Content-Encoding");
if (contentEncoding != null && contentEncoding.getValue().equalsIgnoreCase("gzip")) {
inputStream = new GZIPInputStream(inputStream);
}
String resultString = convertStreamToString(inputStream);
inputStream.close();
return new GsonBuilder().create().fromJson(resultString, objectClass);
}
return null;
}
And this is my ProductDetail class -
public class ProductDetail {
public int Id;
public String Name;
}
On running this, I am getting below error -
No-args constructor for class com.compa.ProductDetail does not exist. Register an InstanceCreator with Gson for this type to fix this problem.
This is thrown on this line in JSONHttpClient file -
return new GsonBuilder().create().fromJson(resultString, objectClass);
Can anyone help on this?
In my web api, I am creating json like this (proddetails is a C# IEnumerable object) -
json = JsonConvert.SerializeObject(proddetails);
var response = this.Request.CreateResponse(HttpStatusCode.OK);
response.Content = new StringContent(json, Encoding.UTF8, "application/json");
return response;
The structure of response json is -
[
{
"Id": 1,
"Name": "First"
},
{
"Id": 2,
"Name": "Second"
}
]


The Gson user guide (https://sites.google.com/site/gson/gson-user-guide) tells you that a well behaved class (meant for serialization and deserialization) should have a no argument constructor. If this is not there, it advises you to use InstanceCreator.
Even if you do not have a constructor, Gson will create an ObjectConstructor for your class. But this is not safe always and has it's own limitations. This question on SO goes more into the details: Is default no-args constructor mandatory for Gson?
NOTE: Please see that if this is an inner class, then it MUST have a constructor as explained in the documentation.
EDIT: Your json is an array. So you need to have the specified number of array objects in the containing class. So you can do the following and then cast:
public class ProductDetailArray {
public ProductDetailArray[] array;
public static ProductDetail {
public ProductDetail() {} // You can also make the constructor private if you don't want anyone to instantiate this
public int Id;
public String Name;
}
}
Once you cast your json similarly as before:
ProductDetailArray obj = GsonBuilder.create().fromJson(response, ProductDetailArray.class);
ProductDetail one = obj.array[0];
ProductDetail two = obj.array[1];
And then you can do your manipulation.. also you should probably be using Gson.fromJson() rather than the GsonBuilder

Related

Gson parse response to get generic class

I've a response class
public class ResponseModel<T> {
private boolean isRequestSuccessful;
public boolean getIsRequestSuccessful() {
return this.isRequestSuccessful;
}
public void setIsRequestSuccessful(boolean isRequestSuccessful) {
this.isRequestSuccessful = isRequestSuccessful;
}
private String message;
public String getMessage() {
return this.message;
}
public void setMessage(String message) {
this.message = message;
}
private T object;
public T getObject() {
return this.object;
}
public void setObject(T object) {
this.object = object;
}
}
My API will return type T. I would like to parse the response from the API and create a object of type ResponseModel.
I am trying to achieve something like below which I can do it easily with c#. Please help on how to do this with Java
public static ResponseModel<T> Get(String requestUri) throws ClientProtocolException,IOException {
CloseableHttpClient client = HttpClientBuilder.create().build();
HttpGet httpGet = new HttpGet(requestUri);
httpGet.addHeader("TenantKey", TenantKey);
httpGet.addHeader("accept", "application/json");
HttpResponse response = client.execute(httpGet);
ResponseModel<T> responseModel = new ResponseModel<T>();
if (response.getStatusLine().getStatusCode() == 200) {
Gson gson = new GsonBuilder().create();
// parse the response as T and and assign to object of ResponseModel
responseModel.object = ...
}
else
{
responseModel.message = response.getEntity().getContent();
}
// return ResponseModel here
}

Generics in C# and Java are pretty different. Simply spoken, there is no sense in what you are doing here.
The java generic T you are using there is a compile time feature. It allows you to use more specific types at compile time, instead of using Object all over the place.
Therefore you can't use generics to determine a "T" at "runtime", as you probably intend to. That T in your method comes from the "outside", and the compiler determines that in occasion it should be a ResponseModel<Integer> and ResponseModel<Whatever> in another context.
You can't have gson read JSON data to return a specific ResponseModel<Whatever> for you. If at all, you might be able to use TypeAdapter magic that does some switching based on the actual value, to return this or that specific ResponseModel<Foo>.
Beyond that: when using such bean like classes as your ResponseModel, you simply want them to be specific, not generic.

Not sure, but I had a similar requirement, but its for Android though. Here is the reference link, where I had to write a generic class to load the different forms of JSON from Assets folder and parse to POJO class.
https://github.com/gokulnathperiasamy/Android-Helper/blob/master/JSONHelper.java
Code:
private static String convertJSONtoEntity(String jsonString, String typeString) {
String jsonObjectString = null;
try {
JSONObject jsonObject = new JSONObject(jsonString);
jsonObjectString = jsonObject.get(typeString).toString();
} catch (Exception e) {
Log.e(TAG, e.getLocalizedMessage());
}
return jsonObjectString;
}
private static <T> List<T> fromJsonList(String json, Class<T> clazz) {
Object[] array = (Object[]) java.lang.reflect.Array.newInstance(clazz, 0);
array = new Gson().fromJson(json, array.getClass());
List<T> list = new ArrayList<>();
if (array != null && array.length > 0) {
for (Object anArray : array) {
list.add(clazz.cast(anArray));
}
}
return list;
}
Usage:
Invoke convertJSONtoEntity() with your jsonString and typeString will be your root element of your JSON.
Invoke the fromJsonList() with value returned by convertJSONtoEntity() and Class. This gives list of objects from JSON.

With the help of other answers and further searching in Google, I ended up with the following code
public static <T> ResponseModel<T> Get(Class<?> classType, String requestUri) throws ClientProtocolException, IOException
{
CloseableHttpClient client = HttpClientBuilder.create().build();
HttpGet httpGet = new HttpGet(requestUri);
httpGet.addHeader("accept", "application/json");
HttpResponse response = client.execute(httpGet);
ResponseModel<T> responseModel = new ResponseModel<T>();
if (response.getStatusLine().getStatusCode() == 200)
{
responseModel.setObject((T) Utils.fromJson(EntityUtils.toString(response.getEntity()), classType));
responseModel.setIsRequestSuccessful(true);
}
else
{
responseModel.setMessage(response.getEntity().getContent().toString());
responseModel.setIsRequestSuccessful(false);
}
return responseModel;
}

Mockito when() doesn't differentiate between child classes

I wrote a test that uses Mockito 1.9.5. I have an HttpGet and an HttpPost which an HttpClient execute, and I'm testing to verify that the response from each returns the expected result in the form of an input stream.
The issue is that while using
Mockito.when(mockedClient.execute(any(HttpPost.class))).thenReturn(postResponse) and Mockito.when(mockedClient.execute(any(HttpGet.class))).thenReturn(getResponse), where the responses are different objects, mockedClient.execute() always returns getResponse.
The test I've written is below:
private InputStream postContent;
private InputStream getContent;
#Mock
private FilesHandler hand;
#Mock
private MockHttpClient client;
private MockHttpEntity postEntity;
private MockHttpEntity getEntity;
private MockHttpResponse postResponse;
private MockHttpResponse getResponse;
private String imgQuery = "someQuery";
private ParametersHandler ph;
private FileHandlerImpl fileHand;
private String indexFolder = "src/test/resources/misc/";
private String indexFile = "index.csv";
#Before
public void setUp() {
MockitoAnnotations.initMocks(this);
try {
postContent = new FileInputStream(indexFolder + "testContent.txt");
postEntity = new MockHttpEntity(postContent);
postResponse = new MockHttpResponse(postEntity, new BasicStatusLine(new ProtocolVersion("http", 1, 1), 200, "postReasonPhrase"));
getContent = new FileInputStream(indexFolder + "testContent.txt");
getEntity = new MockHttpEntity(getContent);
getResponse = new MockHttpResponse(getEntity, new BasicStatusLine(new ProtocolVersion("http", 1, 1), 200, "getReasonPhrase"));
ph = new ParametersHandler();
fileHand = new FileHandlerImpl(client, ph, indexFolder, indexFile);
} catch (Exception e) {
failTest(e);
}
}
#Test
public void getFileWhenEverythingJustWorks() {
try {
Mockito.when(client.execute(Mockito.any(HttpPost.class))).thenReturn(postResponse);
Mockito.when(client.execute(Mockito.any(HttpGet.class))).thenReturn(getResponse);
fileHand.getFile(hand, imgQuery, ph, "I");
Mockito.verify(hand).rebuildIndex(Mockito.any(String.class), Mockito.any(Map.class), Mockito.any(Map.class), hand);
} catch (IOException e) {
failTest(e);
}
}
A shortened version of the method being tested is below.
public void getFile(FilesHandler fileHandlerFl, String query, ParametersHandler ph, String type) {
JsonFactory factory = new JsonFactory();
HttpPost post = preparePost(query, factory);
CloseableHttpResponse response = client.execute(post);
String uri = "https://someuri.com" + "/File";
HttpGet get = new HttpGet(uri);
setParameters(get);
response.close();
response = client.execute(get);
}
As always, any help you can provide is appreciated.

Despite what it would mean when read in English, in Mockito 1.x, any(HttpGet.class) matches any value and not just any HttpGet. The parameter is only used to save a cast previous to Java 8.
From the Matchers.any(Class) documentation:
Matches any object, including nulls
This method doesn't do type checks with the given parameter, it is only there to avoid casting in your code. This might however change (type checks could be added) in a future major release.
Use isA(HttpGet.class) and isA(HttpPost.class) instead, and see Brice's comment below about future changes to the any(Class<?> clazz) matcher.

Json Get/Send Data Strategies

Now I'm learning how to use Gson library to set and get data from webservice in Json format, but its best practices and strategies are a bit dark for me so I will be very delightful if somebody would explain more about it.
I've created an Entity class to get response entity from server:
public class Response
{
#SerializedName("Type")
public String Type;
#SerializedName("result")
public String result;
}
and in AsyncTask class I've used:
Response _Response = new Response();
try
{
String _url = Global.Url_Request ;
Map<String, String> Params = new HashMap<String, String>();
Params.put("PhoneNumber", this.User_PhoneNumber);
String json = new GsonBuilder().create().toJson(Params, Map.class);
HttpClient httpclient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(_url);
httpPost.setEntity(new StringEntity(json));
httpPost.setHeader("Accept", "application/json");
httpPost.setHeader("Content-type", "application/json");
HttpResponse getResponse = httpclient.execute(httpPost);
HttpEntity returnEntity = getResponse.getEntity();
is = returnEntity.getContent();
Gson gson = new Gson();
Reader reader = new InputStreamReader(is);
_Response = gson.fromJson(reader, Response.class);
}
catch (Exception e)
{
_Response.Type= "Error";
_Response.result= "Data Is Wrong";
}
return _Response;
It works fine with creating an Entity Object for every different http POST call, but my questions are:
What is the best practice for handling webservices with different response objects?
How can I handle this situation: if data sent ok then return specific Jsonarray; if not, return a Response object to detect something is wrong. Should I use Custom typeAdapter?(sample code would be great)
If webservice returns an empty response gson.fromJson would throw an **IllegalStateException: Expected a string but was BEGIN_OBJECT** how can i prevent this?
Thanks in advance

1. What is the best practice for handling webservices with different response objects?
I think that this depends on the kind of control you have. If you code also the webservice, you could create a big container object that has may fields. Each of these fields is one of the possible responses you can pass between client and server. If you have not control on what the server can reply, and it can differ a lot, JsonParser is your best friend. You can use it to snoop inside JSON and decide the right strategy to handle the response.
Let's do an example for case one. I declare these classes:
public static class GenericResponse{
public ServerException exception;
public StandardResponse1 responseType1;
public StandardResponse2 responseType2;
#Override
public String toString() {
return "GenericResponse [exception=" + exception + ", responseType1=" + responseType1 + ", responseType2=" + responseType2 + "]";
}
}
public static class ServerException{
public int error;
public String message;
}
public static class StandardResponse1{
public List<Integer> list;
public Date now;
}
With this kind of classes, I can parse:
{"responseType1":{"list":[1,2],"now":"Nov 25, 2013 9:26:51 PM"}}
or
{"exception":{"error":-1,"message":"Don\u0027t do this at home"}}
For example, if I get from server the second type of response, this code:
GenericResponse out = g.fromJson(fromServerStream, GenericResponse.class);
System.out.println(out);
will return me:
GenericResponse [exception=stackoverflow.questions.Q20187804$ServerException#1e9d085, responseType1=null, responseType2=null]
All you have to do is to check your fields to see what actually the server replied.
Case two. You cannot control the JSON, so the server can reply
[13,17]
or
{"error":-1,"message":"Don\u0027t do this at home"}
In this case you cannot pass directly the class type to Gson as before, but you have to check things. I would solve this problem with a JsonParser.
Gson g = new Gson();
JsonParser jp = new JsonParser();
JsonElement o = jp.parse(s);
if (o.isJsonArray()){
List<Integer> list = (List) g.fromJson(o, listType1);
System.out.print(list);
}
else{
ServerException e = g.fromJson(s, ServerException.class);
System.out.print(e);
}
Using JsonObject/JsonArray and so on, is what happens inside a TypeAdapter. In the adapter you start with the JsonElement that is already parsed. There are many good example of it on SO, this for example.
How can I handle this situation: if data sent ok then return specific Jsonarray; if not, return a Response object to detect something is wrong. Should I use Custom typeAdapter?(sample code would be great)
Do you mean you want to parse this kind of response? Examples of point 1 show this.
If webservice returns an empty response gson.fromJson would throw an **IllegalStateException: Expected a string but was BEGIN_OBJECT how can i prevent this?**
JsonParser/TypeAdapter is again the solution. You can check if JsonElement is null or if is a primitive type (String, Integer, Boolean) and deal it.

Java convert Json array to typed List<T>

I have a webservice that sends a typed arraylist which I capture via HttpResponse like so:
// create GET request
HttpGet httpGet = new HttpGet("http://localhost:8084/MinecraftRestServer/webresources/Items");
// execute GET request
HttpResponse response = client.execute(httpGet);
// check response
StatusLine statusLine = response.getStatusLine();
int statusCode = statusLine.getStatusCode();
if (statusCode == 200) { // response OK
// retreive response
List<Recipe> recipesList = new ArrayList<Recipe>();
HttpEntity jsonObj = response.getEntity();
//What's next?
The array that's being sent from the webservice looks like this:
recipesList.add(new Item(1, 11, "diamond_ingot", "Diamond ingot",
"0,0,0,0,0,0,0,0,1", "air,diamond_ore"));
recipesList.add(new Item(2, 11, "iron_ingot", "Iron ingot",
"0,0,0,0,0,0,0,0,1", "air,iron_ore"));
And comes out in this format:
[{"recipeCategory":11,"recipeImageID":"diamond_ingot","recipeDescription":"Diamond ingot","recipeLocations":"0,0,0,0,0,0,0,0,1","usedImages":"air,diamond_ore","recipeID":1},{"recipeCategory":11,"recipeImageID":"iron_ingot","recipeDescription":"Iron ingot","recipeLocations":"0,0,0,0,0,0,0,0,1","usedImages":"air,iron_ore","recipeID":2},{"recipeCategory":11,"recipeImageID":"gold_ingot","recipeDescription":"Gold ingot","recipeLocations":"0,0,0,0,0,0,0,0,1","usedImages":"air,gold_ore","recipeID":3},{"recipeCategory":11,"recipeImageID":"diamond_ore","recipeDescription":"Diamond ore","recipeLocations":"0,0,0,0,0,0,0,0,1","usedImages":"air,wooden_pickaxe","recipeID":4},{"recipeCategory":11,"recipeImageID":"iron_ore","recipeDescription":"Iron ore","recipeLocations":"0,0,0,0,0,0,0,0,1","usedImages":"air,wooden_pickaxe","recipeID":5},{"recipeCategory":11,"recipeImageID":"gold_ore","recipeDescription":"Gold ore","recipeLocations":"0,0,0,0,0,0,0,0,1","usedImages":"air,wooden_pickaxe","recipeID":6},{"recipeCategory":2,"recipeImageID":"diamond_boots","recipeDescription":"Boots (Diamond)","recipeLocations":"0,0,0,1,0,1,1,0,1","usedImages":"air,diamond_ingot","recipeID":7},{"recipeCategory":2,"recipeImageID":"gold_boots","recipeDescription":"Boots (Gold)","recipeLocations":"0,0,0,1,0,1,1,0,1","usedImages":"air,gold_ingot","recipeID":8},{"recipeCategory":2,"recipeImageID":"iron_boots","recipeDescription":"Boots (Iron)","recipeLocations":"0,0,0,1,0,1,1,0,1","usedImages":"air,iron_ingot","recipeID":9},{"recipeCategory":2,"recipeImageID":"diamond_leggings","recipeDescription":"Leggings (Diamond)","recipeLocations":"1,1,1,1,0,1,1,0,1","usedImages":"air,diamond_ingot","recipeID":10},{"recipeCategory":2,"recipeImageID":"gold_leggings","recipeDescription":"Leggings (Gold)","recipeLocations":"1,1,1,1,0,1,1,0,1","usedImages":"air,gold_ingot","recipeID":11},{"recipeCategory":2,"recipeImageID":"iron_leggings","recipeDescription":"Leggings (Iron)","recipeLocations":"1,1,1,1,0,1,1,0,1","usedImages":"air,iron_ingot","recipeID":12},{"recipeCategory":2,"recipeImageID":"diamond_chestplate","recipeDescription":"Chestplate (Diamond)","recipeLocations":"1,0,1,1,1,1,1,1,1","usedImages":"air,diamond_ingot","recipeID":13},{"recipeCategory":2,"recipeImageID":"gold_chestplate","recipeDescription":"Chestplate (Gold)","recipeLocations":"1,0,1,1,1,1,1,1,1","usedImages":"air,gold_ingot","recipeID":14},{"recipeCategory":2,"recipeImageID":"iron_chestplate","recipeDescription":"Chestplate (Iron)","recipeLocations":"1,0,1,1,1,1,1,1,1","usedImages":"air,iron_ingot","recipeID":15},{"recipeCategory":2,"recipeImageID":"diamond_helmet","recipeDescription":"Helmet (Diamond)","recipeLocations":"1,1,1,1,0,1,0,0,0","usedImages":"air,diamond_ingot","recipeID":16},{"recipeCategory":2,"recipeImageID":"gold_helmet","recipeDescription":"Helmet (Gold)","recipeLocations":"1,1,1,1,0,1,0,0,0","usedImages":"air,gold_ingot","recipeID":17},{"recipeCategory":2,"recipeImageID":"iron_helmet","recipeDescription":"Helmet
My question is, how can I convert this back into an arraylist (ArrayList<Item>)
There is already an Item class present in the client application.
I've read examples about the Gson library but it seems it's not included anymore when compiling in API 17.
What would be the easiest approach?

Download and include GSON jar from here in your project if using Eclipse.
If using Android Studio then open your build.gradle and add the below to your dependencies block. Or again you can choose not to use maven and simply drop the jar in your lib folder.
compile 'com.google.code.gson:gson:2.2.4'
Next, use GSON to construct a list of items.
Make sure you have your Item.java class with same member names as in the JSON response
List<Recipe> recipesList = new ArrayList<Recipe>();
HttpEntity jsonObj = response.getEntity();
String data = EntityUtils.toString(entity);
Log.d("TAG", data);
Gson gson = new GsonBuilder().create();
recipesList = gson.fromJson(data, new TypeToken<List<Item>>() {}.getType());
Make sure you handle the exceptions appropriately.

You could use Jackson to parse the incoming JSON. (Quick introduction)
If you already have a Class with the appropriate properties, it can be as easy as something like this:
public class Items {
private List<Item> items;
// getter+setter
}
ObjectMapper mapper = new ObjectMapper();
Items = mapper.readValue(src, Items.class);
See this for more information.

Step 1 : Item obj=new Item;
Step 2: Parse the json formar for example here :
[[Example1][1]
Step 3: while parsing put ur values in obj :
obj.recipeCategory=value1;
Step 4: insret ur obj into arraylist:
arrayList.add(obj);

I think you should using json-simple library to parse string Json to JsonObject and convert to simple data type.
Example:
JSONArray arrJson = (JSONArray) parser.parse("String json");
Get each element JSONObject in JSONArray, then parse it to simple data type:
long recipeCategory = (long) jsonObject.get("recipeCategory");

You can use Gson like many users said, here is an example of a RESTfull client using Gson:
public class RestRequest {
Gson gson = new Gson();
public <T> T post(String url, Class<T> clazz,
List<NameValuePair> parameters) {
// Create a new HttpClient and Post Header
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(url);
try {
// Add your data
httppost.setEntity(new UrlEncodedFormEntity(parameters));
// Execute HTTP Post Request
HttpResponse response = httpclient.execute(httppost);
StringBuilder json = inputStreamToString(response.getEntity()
.getContent());
T gsonObject = gson.fromJson(json.toString(), clazz);
return gsonObject;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
// Fast Implementation
private StringBuilder inputStreamToString(InputStream is)
throws IOException {
String line = "";
StringBuilder total = new StringBuilder();
// Wrap a BufferedReader around the InputStream
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
// Read response until the end
while ((line = rd.readLine()) != null) {
total.append(line);
}
// Return full string
return total;
}
}
The usage will be something like this:
new RestRequest("myserver.com/rest/somewebservice", SomeClass.class, Arrays.asList(new BasicValuePair("postParameter", "someParameterValue")));
Where SomeClass.class will be Recipe[].class in your case. Also check this question to properly handle server side errors.

Man, google is your friend! A quick search for "android json" or "android json parse" gives you some nice tutorials like this one or this here.

Android SDK: Parsing JSON from URL using GSON

I am trying to parse JSON from a URL to then add data to an array.
I am using the GSON library.
My JSON has the following format:
[
{
"img-src":"http://website.com/images/img1.png",
"URL":"http://google.com"
},
{
"img-src":"http://website.com/images/img2.jpg",
"URL":"http://yahoo.com"
}
]
I want to grab the above data in a separate thread, I have the following code:
public class Async extends AsyncTask<String, Integer, Object>{
#Override
protected String doInBackground(String... params) {
return null;
}
}
How do I go about grabbing each "img-src" and "URL" values?

Use this method to fetch your Data in an Array list
public ArrayList<NewsItem> getNews(String url) {
ArrayList<NewsItem> data = new ArrayList<NewsItem>();
java.lang.reflect.Type arrayListType = new TypeToken<ArrayList<NewsItem>>(){}.getType();
gson = new Gson();
httpClient = WebServiceUtils.getHttpClient();
try {
HttpResponse response = httpClient.execute(new HttpGet(url));
HttpEntity entity = response.getEntity();
Reader reader = new InputStreamReader(entity.getContent());
data = gson.fromJson(reader, arrayListType);
} catch (Exception e) {
Log.i("json array","While getting server response server generate error. ");
}
return data;
}
This should be how you should declare your ArrayList Type class (here its NewsItem)
import com.google.gson.annotations.SerializedName;
public class NewsItem {
#SerializedName("title")
public String title;
#SerializedName("content")
public String title_details;
#SerializedName("date")
public String date;
#SerializedName("featured")
public String imgRawUrl;
}
Here is the WebSErvice Util Class.
public class WebServiceUtils {
public static HttpClient getHttpClient(){
HttpParams httpParameters = new BasicHttpParams();
// Set the timeout in milliseconds until a connection is established.
int timeoutConnection = 50000;
HttpConnectionParams.setConnectionTimeout(httpParameters, timeoutConnection);
// Set the default socket timeout (SO_TIMEOUT)
// in milliseconds which is the timeout for waiting for data.
int timeoutSocket = 50000;
HttpConnectionParams.setSoTimeout(httpParameters, timeoutSocket);
HttpClient httpclient = new DefaultHttpClient(httpParameters);
return httpclient;
}
}

That's the code I use (working well for me).
//Initialize the list
Type listType = new TypeToken<ArrayList<YourObject>>(){}.getType();
//Parse
List<YourObject> List= new Gson().fromJson(response, listType);
YourObject should be something like :
public class Category {
private String URL;
private String img-src;
public Category(String URL, String img-src){
this.URL= URL;
this.img-src= img-src;
}
}
Regards.
Ps: With this you will obtain a list of "YourObject". Then you can create to list one with the URL and other with img-src

In this user guide you can find a lot of examples:
https://sites.google.com/site/gson/gson-user-guide

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