MainActivity.java
package com.example.yashpachisia.fetchjson;
import android.os.AsyncTask;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.BasicHttpParams;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
public class MainActivity extends ActionBarActivity {
String myJSON;
private static final String TAG_RESULTS="result";
private static final String TAG_NAME = "name";
private static final String TAG_AGE = "age";
private static final String TAG_SEX ="sex";
JSONArray peoples = null;
ArrayList<HashMap<String, String>> personList;
ListView list;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list = (ListView) findViewById(R.id.listView);
personList = new ArrayList<HashMap<String,String>>();
getData();
}
protected void showList(){
try {
JSONObject jsonObj = new JSONObject(myJSON);
peoples = jsonObj.getJSONArray(TAG_RESULTS);
for(int i=0;i<peoples.length();i++){
JSONObject c = peoples.getJSONObject(i);
String name = c.getString(TAG_NAME);
String age = c.getString(TAG_AGE);
String sex = c.getString(TAG_SEX);
HashMap<String,String> persons = new HashMap<String,String>();
persons.put(TAG_NAME,name);
persons.put(TAG_AGE,age);
persons.put(TAG_SEX,sex);
personList.add(persons);
}
ListAdapter adapter = new SimpleAdapter(
MainActivity.this, personList, R.layout.list_item,
new String[]{TAG_NAME,TAG_AGE,TAG_SEX},
new int[]{R.id.name, R.id.age, R.id.sex}
);
list.setAdapter(adapter);
} catch (JSONException e) {
e.printStackTrace();
}
}
public void getData(){
class GetDataJSON extends AsyncTask<String, Void, String>{
@Override
protected String doInBackground(String... params) {
DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
HttpPost httppost = new HttpPost("http://localhost/test/form.php");
// Depends on your web service
httppost.setHeader("Content-type", "application/json");
InputStream inputStream = null;
String result = null;
try {
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
inputStream = entity.getContent();
// json is UTF-8 by default
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null)
{
sb.append(line + "\n");
}
result = sb.toString();
} catch (Exception e) {
// Oops
}
finally {
try{if(inputStream != null)inputStream.close();}catch(Exception squish){}
}
return result;
}
@Override
protected void onPostExecute(String result){
myJSON=result;
showList();
}
}
GetDataJSON g = new GetDataJSON();
g.execute();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
/* @Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_user) {
return true;
}
return super.onOptionsItemSelected(item);
}*/
}
清单
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.yashpachisia.fetchjson">
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
Logcat窗口
12-19 17:17:59.353 5132-5132/? D/OpenGLRenderer: Enabling debug mode 0
12-19 17:17:59.353 5132-5132/? D/AndroidRuntime: Shutting down VM
12-19 17:17:59.357 5132-5132/? W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xa6299288)
12-19 17:17:59.357 5132-5132/? E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
at org.json.JSONTokener.nextValue(JSONTokener.java:94)
at org.json.JSONObject.<init>(JSONObject.java:154)
at org.json.JSONObject.<init>(JSONObject.java:171)
at com.example.yashpachisia.fetchjson.MainActivity.showList(MainActivity.java:56)
at com.example.yashpachisia.fetchjson.MainActivity$1GetDataJSON.onPostExecute(MainActivity.java:128)
at com.example.yashpachisia.fetchjson.MainActivity$1GetDataJSON.onPostExecute(MainActivity.java:89)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
只有在检查showList()中的结果不为空或空
onPostExecute()
if(result != null && result.length >0 ){
myJSON=result;
showList()
}
由于您的myJson可能为空，因此您尝试在其上运行Json代码，因此您将获得NulPointerError
更新
如果您获得空值，则表示您没有从Web服务获取数据，或者您调用的是错误的。
我在你的代码中看到了一些错误，所以我给你写了一个新错误。我的代码使用commons-io-2.4.jar库，但您总是可以编写自己的代码来查看结果
String chartString = "your url which you want to call";
URL chartURL = new URL(chartString);
HttpURLConnection chartHttpURLConnection = (HttpURLConnection) chartURL.openConnection();
chartHttpURLConnection.connect();
String result = IOUtils.toString(chartHttpURLConnection.getInputStream());
System.out.println(""+result);
因为您尝试通过模拟器调用本地服务，因此IP地址将为10.0.2.2
所以你要调用的网址是
URL url = new URL(http://10.0.2.2/test/form.php);