无法从网络服务器获取数据
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【中文标题】无法从网络服务器获取数据【英文标题】：Trouble in getting data from webserver 【发布时间】：2013-04-30 15:33:33 【问题描述】：我编写这段代码是为了从网络服务器（mysql 数据库）读取和写入数据，然后所有数据都将显示在我的安卓应用程序上。
在这方面，我使用 php 服务从 Web 服务器读取和写入数据。一切正常，它可以正确地从 Web 服务器获取数据，但是当它到达这一行时：
int success = jsonObject.getInt(TAG_SUCCESS);
它显示了一个空指针异常，我不知道为什么，但它实际上让我发疯了。
代码：
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.commons.collections.*;
//import org.json.JSONObject;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ProgressDialog;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import org.json.*;
public class MiddleActivity extends Activity
Button btnMiddleDB;
ProgressDialog pDialog ;
JSONParser jsonParser = new JSONParser();
JSONArray places = null;
private static final String URL = "http://192.168.1.2/android_connect/get_all_products.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "products";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";
ArrayList<HashMap<String, String>> placesList;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_middle);
new LoadGettingFromDatabase().execute();
btnMiddleDB = (Button) findViewById(R.id.button1);
btnMiddleDB.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View arg0)
);
运行后台线程以从网络服务器获取数据
class LoadGettingFromDatabase extends AsyncTask<String, String, String>
@Override
protected void onPreExecute()
super.onPreExecute();
pDialog = new ProgressDialog(MiddleActivity.this);
pDialog.setMessage("Getting from database...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
**after getting data from webserver parse it to json and store it into string**
@Override
protected String doInBackground(String... args)
List<NameValuePair> params = new ArrayList<NameValuePair>();
Log.d("Seen","seen1");
JSONObject jsonObject = jsonParser.makeHttpRequest(URL, "GET" ,params);
Log.d("String","JSON 2");
//Log.d("All entries","Entries" + jsonObject.toString());
try
Log.d("Seen","seen2");
其实问题就在这里
int success = jsonObject.getInt(TAG_SUCCESS);
Log.d("Seen","seen5");
if(success == 1)
//Entries found
Log.d("Seen","seen6");
places = jsonObject.getJSONArray(TAG_PRODUCTS);
for(int i=0;i<places.length();i++)
JSONObject temp = places.getJSONObject(i);
String id = temp.getString(TAG_PID);
String name = temp.getString(TAG_NAME);
HashMap<String, String> hashMap = new HashMap<String, String>();
hashMap.put(TAG_PID, id);
hashMap.put(TAG_NAME, name);
placesList.add(hashMap);
catch (Exception e)
Log.e("success","success status " + e);
return null;
public void onProExecute(String file_url)
pDialog.dismiss();
runOnUiThread(new Runnable()
public void run()
ListAdapter listAdapter = new SimpleAdapter(MiddleActivity.this, placesList, R.layout.list_item, new String[]
TAG_PID, TAG_NAME,new int[]R.id.ID, R.id.Name);
ListView listView = (ListView) findViewById(R.layout.list_item);
listView.setAdapter(listAdapter);
;
);
;
@Override
public boolean onCreateOptionsMenu(Menu menu)
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_middle, menu);
return true;
**and log cat is**
05-07 00:29:54.419: D/Seen(30282): seen1
05-07 00:29:54.569: D/Seen(30282): seen3
05-07 00:29:54.909: D/Seen(30282): seen4
05-07 00:29:54.979: D/String(30282): JSON get_all_products.php
05-07 00:29:54.979: D/String(30282): db_connect.php
05-07 00:29:54.979: D/String(30282): db_config.php
05-07 00:29:54.979: D/String(30282): "success":0,"message":"No products found
05-07 00:29:55.300: D/String(30282): JSON 1
05-07 00:29:55.300: D/String(30282): JSON 2
05-07 00:29:55.310: D/Seen(30282): seen2
**05-07 00:29:55.310: E/success(30282): success status
java.lang.NullPointerException**
and here is my jsonparser class
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser()
// function get json from url
// by making HTTP POST or GET method
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params)
// Making HTTP request
try
// check for request method
if(method == "POST")
// request method is POST
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
else if(method == "GET")
// request method is GET
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
catch (UnsupportedEncodingException e)
e.printStackTrace();
catch (ClientProtocolException e)
e.printStackTrace();
catch (IOException e)
e.printStackTrace();
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();
json = sb.toString();
catch (Exception e)
Log.e("Buffer Error", "Error converting result " + e.toString());
// try parse the string to a JSON object
try
jObj = new JSONObject(json);
catch (JSONException e)
Log.e("JSON Parser", "Error parsing data " + e.toString());
// return JSON String
return jObj;
【问题讨论】：
【参考方案1】：你的 jsonObject 为 null，通过在 line 处设置断点来调试应用程序->
JSONObject jsonObject = jsonParser.makeHttpRequest(URL, "GET" ,params);
并检查jsonObject的值。
【讨论】：
我知道它返回 null。实际上这是要解决的问题：p 我已经发布了请通过以上是关于无法从网络服务器获取数据的主要内容，如果未能解决你的问题，请参考以下文章