Question

我正在做一个项目，我需要通过HttpClient从URL解析JSON。我的代码适用于少量数据的JSON对象响应。但是，当我使用相同的代码获取大量数据（超过3MB）的响应时，我遇到了问题。

这是我的代码：

JSONfunctions.java（用于json解析的函数）

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
//import java.util.HashMap;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
//import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
//import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.util.Log;
import android.widget.Toast;

@SuppressWarnings("unused")
public class JSONfunctions {

    public static JSONObject getJSONfromURL(String url){
        InputStream is = null;
        String result = "";
        JSONObject jArray = null;

        //http post
        try{
                HttpClient httpclient = new DefaultHttpClient();
                HttpPost httppost = new HttpPost(url);
                HttpResponse response = httpclient.execute(httppost);
                HttpEntity entity = response.getEntity();
                is = entity.getContent();

        }catch(Exception e){
                Log.e("log_tag", "Error in http connection "+e.toString());
        }

        //convert response to string
        try{
                BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
                StringBuilder sb = new StringBuilder();
                String line = null;
                while ((line = reader.readLine()) != null) {
                        sb.append(line + "\n");
                }
                is.close();
                result=sb.toString();

            //    Toast.makeText(getBaseContext, result, Toast.LENGTH_LONG).

        }catch(Exception e){
                Log.e("log_tag", "Error converting result "+e.toString());
        }

        try{

            jArray = new JSONObject(result);            
        }catch(JSONException e){
                Log.e("log_tag", "Error parsing data "+e.toString());
        }

        return jArray;
    }
}

ListJson.java

import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
//import org.w3c.dom.Document;
//import org.w3c.dom.Element;
//import org.w3c.dom.NodeList;



import android.app.ListActivity;
import android.content.Intent;
//import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;


public class ListJson extends ListActivity {
     public static JSONObject json;
     public static JSONArray data;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list1);

        ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
     //   String semail = "partha@excoflare.com";
      //  String spassword = "partha123";


      //  Toast.makeText(getApplicationContext(), JSONExample2.strEmail, Toast.LENGTH_LONG).show();
        //Toast.makeText(getApplicationContext(), JSONExample2.strPwd, Toast.LENGTH_LONG).show();

        //    

        json = JSONfunctions.getJSONfromURL("url here");      


            try{

            data = json.getJSONArray("server_list");


            for(int i=0;i<data.length();i++){                       
                HashMap<String, String> map = new HashMap<String, String>();    
                JSONObject e = data.getJSONObject(i);

                map.put("id", String.valueOf(i));
                map.put("name", "" + e.getString("ServUser"));
                map.put("email", "" + e.getString("ServURL"));
                mylist.add(map);
            }       
        }catch(JSONException e)        {
             Log.e("log_tag", "Error parsing data "+e.toString());
        }


//        try {
//          JSONObject newObject=json.getJSONObject("subscription");
//          JSONArray data1 = newObject.getJSONArray("cust_product");
//          
//          Toast.makeText(getApplicationContext(), data1.toString(), Toast.LENGTH_LONG).show();
//         
//          for(int i=0;i<data1.length();i++){                      
//                  HashMap<String, String> map1 = new HashMap<String, String>();   
//                  JSONObject e = data.getJSONObject(i);
//                  
//                  map1.put("id", String.valueOf(i));
//                  map1.put("name", "" + e.getString("ServUser"));
//                  map1.put("email", "" + e.getString("ServURL"));
//                  mylist.add(map1);
//              }       
//          
//      } catch (JSONException e) {
//          // TODO Auto-generated catch block
//          e.printStackTrace();
//      }


         ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.item_list,
                                  new String[] { "name", "email" }, 
                              new int[] { R.id.item_title, R.id.item_subtitle });
                                  setListAdapter(adapter);


      final ListView lv = getListView();
       lv.setTextFilterEnabled(true);   
        lv.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {              
                //@SuppressWarnings("unchecked")
                //HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);                 
            //  Toast.makeText(ListJson.this, "ID '" + o.get("id") + "' was clicked.", Toast.LENGTH_SHORT).show(); 

                Toast.makeText(getApplicationContext(), parent.getItemAtPosition(position).toString(),
                        Toast.LENGTH_LONG).show();

            //   String a= parent.getItemAtPosition(position).toString();

                Intent intent2= new Intent(ListJson.this, ListJson2.class);
                 startActivity(intent2);
            }
        }); 

    }

我得到OutOfMemoryException。我将heap_size更改为192MB，将ram大小更改为32MB，但没有运气。我该如何解决这个问题？

Answer 1

JSON的大量数据必须削减成小块。例如，您的数据库中有50000个产品。然后分页API请求是明智的 - 在一次查询中获得100-500条记录的大量产品。这将解决您的问题。

这种方法更多地解决了一个问题 - 因互联网和gprs连接丢失等引起的错误。

如果API是您的，那么您可以更改它。如果没有，那么这是API设计的一大失败，您可以发送更改请求。

编辑：

做了一点阅读，发现强烈推荐用于解析大量JSON数据的负载是http://jackson.codehaus.org/（Jackson Processor）。没试过，所以无法评论这个库。还建议您将此JSON流保存到文件中（不要将其加载到内存中），然后通过块解析它。

解析大型JSON响应时出现OutOfMemoryException

JSONfunctions.java（用于json解析的函数）

ListJson.java

1 个答案: