获取JSON时出现java空指针异常
这是我的代码,它在从url获取json时抛出java空指针异常。我在android清单中授予了internet权限,现在在新线程中获取url,因为它不允许在主线程中进行网络活动获取JSON时出现java空指针异常,java,android,json,Java,Android,Json,这是我的代码,它在从url获取json时抛出java空指针异常。我在android清单中授予了internet权限,现在在新线程中获取url,因为它不允许在主线程中进行网络活动 package com.example.usa; import java.util.ArrayList; import java.util.HashMap; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONO
package com.example.usa;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
public class Home extends Activity {
// url to make request
private static String url = "http://api.androidhive.info/contacts/";
// JSON Node names
private static final String TAG_CONTACTS = "contacts";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";
private static final String TAG_EMAIL = "email";
private static final String TAG_ADDRESS = "address";
private static final String TAG_GENDER = "gender";
private static final String TAG_PHONE = "phone";
private static final String TAG_PHONE_MOBILE = "mobile";
private static final String TAG_PHONE_HOME = "home";
private static final String TAG_PHONE_OFFICE = "office";
JSONArray contacts = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
final ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();
// Creating JSON Parser instance
final JSONParser jParser = new JSONParser();
final JSONObject json = null ;
// getting JSON string from URL
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
Thread thread = new Thread()
{
@Override
public void run() {
try {
while(true) {
JSONObject json = jParser.getJSONFromUrl(url);
sleep(1000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
thread.start();
//
finish();
}
}, 5000);
// JSONObject json = jParser.getJSONFromUrl(url);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
try {
// Getting Array of Contacts
contacts = json.getJSONArray(TAG_CONTACTS);
// looping through All Contacts
for(int i = 0; i < contacts.length(); i++){
JSONObject c = contacts.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_ID);
String name = c.getString(TAG_NAME);
String email = c.getString(TAG_EMAIL);
String address = c.getString(TAG_ADDRESS);
String gender = c.getString(TAG_GENDER);
// Phone number is agin JSON Object
JSONObject phone = c.getJSONObject(TAG_PHONE);
String mobile = phone.getString(TAG_PHONE_MOBILE);
String home = phone.getString(TAG_PHONE_HOME);
String office = phone.getString(TAG_PHONE_OFFICE);
///////////////////////////
Log.w("ID",id);
Log.w("Name",name);
Log.w("Email",email);
Log.w("Gender",gender);
Log.w("mobile",mobile);
Log.w("home",home);
Log.w("office",office);
Log.w("address",address);
///////////////////
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_ID, id);
map.put(TAG_NAME, name);
map.put(TAG_EMAIL, email);
map.put(TAG_PHONE_MOBILE, mobile);
// adding HashList to ArrayList
contactList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
}
//
finish();
}
}, 5000);
// TODO Auto-generated method stub
}
}
package com.example.usa;
导入java.util.ArrayList;
导入java.util.HashMap;
导入org.json.JSONArray;
导入org.json.JSONException;
导入org.json.JSONObject;
导入android.app.Activity;
导入android.content.Intent;
导入android.os.Bundle;
导入android.os.Handler;
导入android.util.Log;
公营家庭推广活动{
//发出请求的url
专用静态字符串url=”http://api.androidhive.info/contacts/";
//JSON节点名称
专用静态最终字符串标记_CONTACTS=“CONTACTS”;
私有静态最终字符串标记\u ID=“ID”;
私有静态最终字符串标记_NAME=“NAME”;
私有静态最终字符串标记\u EMAIL=“EMAIL”;
私有静态最终字符串标记_ADDRESS=“ADDRESS”;
私有静态最终字符串标记_GENDER=“GENDER”;
专用静态最终字符串标记_PHONE=“PHONE”;
专用静态最终字符串标记\u PHONE\u MOBILE=“MOBILE”;
专用静态最终字符串标记\u PHONE\u HOME=“HOME”;
专用静态最终字符串标记\u PHONE\u OFFICE=“OFFICE”;
JSONArray联系人=null;
/**在首次创建活动时调用*/
@凌驾
创建时的公共void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
最终ArrayList联系人列表=新ArrayList();
//创建JSON解析器实例
final-JSONParser-jParser=new-JSONParser();
最终JSONObject json=null;
//从URL获取JSON字符串
new Handler().postDelayed(new Runnable()){
@凌驾
公开募捐{
线程线程=新线程()
{
@凌驾
公开募捐{
试一试{
while(true){
JSONObject json=jParser.getJSONFromUrl(url);
睡眠(1000);
}
}捕捉(中断异常e){
e、 printStackTrace();
}
}
};
thread.start();
//
完成();
}
}, 5000);
//JSONObject json=jParser.getJSONFromUrl(url);
new Handler().postDelayed(new Runnable()){
@凌驾
公开募捐{
试一试{
//获取联系人数组
contacts=json.getJSONArray(TAG_contacts);
//通过所有触点循环
对于(int i=0;ivalue
地图放置(标签标识,标识);
地图放置(标签名称、名称);
地图放置(标签、电子邮件、电子邮件);
地图放置(标签、手机、手机);
//将哈希列表添加到ArrayList
联系人列表。添加(地图);
}
}捕获(JSONException e){
e、 printStackTrace();
}
//
完成();
}
}, 5000);
//TODO自动生成的方法存根
}
}
这是堆栈跟踪
10-04 06:39:24.830: D/dalvikvm(777): GC_FOR_ALLOC freed 15K, 4% free 4156K/4288K, paused 42ms, total 45ms
10-04 06:39:24.850: I/dalvikvm-heap(777): Grow heap (frag case) to 5.635MB for 1536016-byte allocation
10-04 06:39:25.040: D/dalvikvm(777): GC_FOR_ALLOC freed <1K, 3% free 5655K/5792K, paused 180ms, total 180ms
10-04 06:39:30.280: D/AndroidRuntime(777): Shutting down VM
10-04 06:39:30.280: W/dalvikvm(777): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
10-04 06:39:30.290: E/AndroidRuntime(777): FATAL EXCEPTION: main
10-04 06:39:30.290: E/AndroidRuntime(777): java.lang.NullPointerException
10-04 06:39:30.290: E/AndroidRuntime(777): at com.example.usa.Home$2.run(Home.java:105)
10-04 06:39:30.290: E/AndroidRuntime(777): at android.os.Handler.handleCallback(Handler.java:730)
10-04 06:39:30.290: E/AndroidRuntime(777): at android.os.Handler.dispatchMessage(Handler.java:92)
10-04 06:39:30.290: E/AndroidRuntime(777): at android.os.Looper.loop(Looper.java:137)
10-04 06:39:30.290: E/AndroidRuntime(777): at android.app.ActivityThread.main(ActivityThread.java:5103)
10-04 06:39:30.290: E/AndroidRuntime(777): at java.lang.reflect.Method.invokeNative(Native Method)
10-04 06:39:30.290: E/AndroidRuntime(777): at java.lang.reflect.Method.invoke(Method.java:525)
10-04 06:39:30.290: E/AndroidRuntime(777): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-04 06:39:30.290: E/AndroidRuntime(777): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-04 06:39:30.290: E/AndroidRuntime(777): at dalvik.system.NativeStart.main(Native Method)
10-04 06:39:34.957: D/dalvikvm(777): GC_FOR_ALLOC freed 261K, 6% free 6445K/6824K, paused 81ms, total 98ms
10-04 06:40:00.868: D/dalvikvm(777): GC_FOR_ALLOC freed 2688K, 36% free 5075K/7880K, paused 39ms, total 43ms
10-04 06:44:25.888: I/Process(777): Sending signal. PID: 777 SIG: 9
10-04 06:39:24.830:D/dalvikvm(777):全部释放15K的GC,4%释放4156K/4288K,暂停42ms,总计45ms
10-04 06:39:24.850:I/dalvikvm堆(777):为1536016字节分配将堆(frag案例)增长到5.635MB
10-04 06:39:25.040:D/dalvikvm(777):你有这条线
JSONObject json = jParser.getJSONFromUrl(url);
但是您还有一个方法变量json,我想您打算稍后使用它。问题是:
JSONObject json = jParser.getJSONFromUrl(url);
在第一个线程中,您将从URL检索数据并将其解析为json,在第一个线程之后不久,您将尝试从json对象中检索数据,该对象很可能没有任何数据,因为它仍然忙于检索数据。
所以这不是一个好主意<代码>从同一线程中的JSON数组中检索和获取数据。这将为您节省很多麻烦。
其次,将json解析数据存储在本地json ob中