Java将Json数组转换为类型列表<T>

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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);

Answer 4

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");

Answer 5

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.

Answer 6

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 .