解析來自Url的Json數據 - 空值返回 - Java

Question

我正在使用Eclipse IDE來解析來自URl的Json數據，但everty時間我運行此代碼，它返回空值。

這是從URL

{ 
    "userId": 1, 
    "id": 1, 
    "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", 
    "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto" 
} 

JSON數據這是POJO類

package com.beto.test.json; 

public class Data { 
    private String id; 

    private String body; 

    private String title; 

    private String userId; 

    public String getId() { 
     return id; 
    } 

    public void setId(String id) { 
     this.id = id; 
    } 

    public String getBody() { 
     return body; 
    } 

    public void setBody(String body) { 
     this.body = body; 
    } 

    public String getTitle() { 
     return title; 
    } 

    public void setTitle(String title) { 
     this.title = title; 
    } 

    public String getUserId() { 
     return userId; 
    } 

    public void setUserId(String userId) { 
     this.userId = userId; 
    } 

    @Override 
    public String toString() { 
     return "ClassPojo [id = " + id + ", body = " + body + ", title = " + title + ", userId = " + userId + "]"; 
    } 
} 

JsonParserUrl.java類

package com.beto.test.json; 

import com.google.gson.Gson; 
import com.google.gson.reflect.TypeToken; 
import org.apache.http.HttpResponse; 
import org.apache.http.client.methods.HttpGet; 
import org.apache.http.impl.client.DefaultHttpClient; 

import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.util.List; 
import java.util.Objects; 

/** 
* Created by BeytullahC on 23.03.2015. 
*/ 
public class JsonParserFromUrl { 
    public static void main(String[] args) { 
     DefaultHttpClient httpClient = null; 
     try { 
      httpClient = new DefaultHttpClient(); 
      HttpResponse response = getResponse("http://jsonplaceholder.typicode.com/posts", httpClient); 
      String outPut = readData(response); 
      System.out.println(outPut); 
      Gson gson = new Gson(); 
      List<Data> fromJson = gson.fromJson(outPut, new TypeToken<List<Data>>(){}.getType()); 
      System.out.println("DATA SIZE : "+fromJson.size()); 
      System.out.println("GET FIRST DATA : "+fromJson.get(0)); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } finally { 
      httpClient.getConnectionManager().shutdown(); 
     } 

    } 

    public static HttpResponse getResponse(String url, DefaultHttpClient httpClient) throws IOException { 
     try { 

      HttpGet httpGet = new HttpGet(url); 
      httpGet.addHeader("accept", "application/json"); 
      HttpResponse response = httpClient.execute(httpGet); 
      return response; 
     } catch (IOException e) { 
      throw e; 
     } 
    } 

    public static String readData(HttpResponse response) throws Exception { 
     BufferedReader reader = null; 
     try { 


      reader = new BufferedReader(new InputStreamReader(
        response.getEntity().getContent())); 
      StringBuffer data = new StringBuffer(); 
      char[] dataLength = new char[1024]; 
      int read; 
      while (((read = reader.read(dataLength)) != -1)) { 
       data.append(dataLength, 0, read); 
      } 
      return data.toString(); 
     } finally { 
      if (reader != null) 
       reader.close(); 
     } 
    } 
} 

TestRunner.java類

package com.beto.test.json; 

    public class TestRunner { 

     public static void main(String[] args) { 
      // TODO Auto-generated method stub 

      try{ 

      Data data = JsonParserfromUrl.getData("http://jsonplaceholder.typicode.com/posts/1"); 
      System.out.println("result:\n" +data); 
     } 
      catch(Exception e) 
      { 
       System.out.println("error"); 
      } 

    }} 

Liberaries補充：

- gson-2.3.1.jar 
- httpclient-4.5.jar 
- commons-logging-1.1.1.jar 
- httpclient-cache-4.4.jar 
- httpmime-4.0.jar 
- commons-codec-1.1.jar 
- httpcore-4.4.jar 

輸出

ClassPojo [id = " null ", body = " null ", title = " null ", userId ="null"] 

請解決這個問題，它不應該返回空值。

Answer 1

首先，您應該獲取JSON字符串，然後將其解析爲Data類。

String yourJsonString = readUrl("http://jsonplaceholder.typicode.com/posts/1"); 

Gson gson = new Gson();   
Data data = gson.fromJson(yourJsonString, Data.class);