Java 无法在Android中获取和显示JSON

我正在构建一个复杂的应用程序，但是我遇到了一个孤立的问题。我的Android应用程序类UserPage.java应该能够从网页中获取字符串，然后将其传递给布局并相应地显示

UserPage.java

package com.example.ams;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.List;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;

public class UserPage extends Activity {
        HttpPost httppost;
        StringBuffer buffer;
        HttpResponse response;
        HttpClient httpclient;
        List<NameValuePair> nameValuePairs;
        ProgressDialog dialog = null;

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.userpage);
            String json = getStudents();
            //System.out.println(json);
            TextView datazer = (TextView) findViewById(R.id.data);
            datazer.setText(json);

        }

public String getStudents(){
    HttpResponse response = null;
    //String classID = "CSD2334";
    try {        
            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet();
            request.setURI(new URI("http://localhost:8080/de.vogella.jersey.first/resources/hello/ids/CSD2334"));
            response = client.execute(request);
            System.out.println(response.toString());
        } catch (URISyntaxException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }   
        return response.toString();
    }


}

我得到的错误是相当普遍的，我似乎找不到任何地方的信息

   03-30 17:36:15.074: E/AndroidRuntime(1458): FATAL EXCEPTION: main
03-30 17:36:15.074: E/AndroidRuntime(1458): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ams/com.example.ams.UserPage}: android.os.NetworkOnMainThreadException
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.os.Looper.loop(Looper.java:137)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.ActivityThread.main(ActivityThread.java:4424)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at java.lang.reflect.Method.invokeNative(Native Method)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at java.lang.reflect.Method.invoke(Method.java:511)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at dalvik.system.NativeStart.main(Native Method)
03-30 17:36:15.074: E/AndroidRuntime(1458): Caused by: android.os.NetworkOnMainThreadException
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at java.net.InetAddress.getAllByName(InetAddress.java:220)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at com.example.ams.UserPage.getStudents(UserPage.java:44)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at com.example.ams.UserPage.onCreate(UserPage.java:31)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.Activity.performCreate(Activity.java:4465)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
03-30 17:36:15.074: E/AndroidRuntime(1458):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
03-30 17:36:15.074: E/AndroidRuntime(1458):     ... 11 more
03-30 17:36:15.363: I/dalvikvm(1458): threadid=3: reacting to signal 3
03-30 17:36:15.434: I/dalvikvm(1458): Wrote stack traces to '/data/anr/traces.txt'
03-30 17:36:15.814: I/dalvikvm(1458): threadid=3: reacting to signal 3
03-30 17:36:15.834: I/dalvikvm(1458): Wrote stack traces to '/data/anr/traces.txt'

任何帮助或指点都将不胜感激，

---

D

您正在主线程上运行http调用，这会导致错误

response = client.execute(request);

上述代码应在新线程上运行

您应该有如下内容：

new Thread( new Runnable() {
        @Override
        public void run() {
            HttpResponse response = null;
            //String classID = "CSD2334";
            try {
                HttpClient client = new DefaultHttpClient();
                HttpGet request = new HttpGet();
                request.setURI(new URI("http://localhost:8080/de.vogella.jersey.first/resources/hello/ids/CSD2334"));
                response = client.execute(request);
                System.out.println(response.toString());
            } catch (URISyntaxException e) {
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return response.toString();
        }
    }).start();

如果要对UI组件进行更新，则应将代码运行到：

    runOnUiThread(new Runnable() {
            @Override
            public void run() {
// runs on the UI thread so update UI here
            }
        });

---

如上文所述，您应该阅读有关当前代码运行的更多信息。考虑使用一个或一个扩展类。关于这一点有很多问题，通过快速搜索，所以我觉得举个例子太多了

这就是全部例外吗？你能粘贴更多信息吗？您的某些对象为空。感谢您的快速回复。我编辑了这个问题以添加错误消息的更多细节。它是哪一行

com.example.ams.UserPage.onCreate（UserPage.java:37）

-

getStudents（）

或

datazer

？我再次编辑了错误-它们不是同一代码。第44行是：response=client.execute（请求）；而31是：String json=getStudents（）；

new Thread( new Runnable() {
        @Override
        public void run() {
            HttpResponse response = null;
            //String classID = "CSD2334";
            try {
                HttpClient client = new DefaultHttpClient();
                HttpGet request = new HttpGet();
                request.setURI(new URI("http://localhost:8080/de.vogella.jersey.first/resources/hello/ids/CSD2334"));
                response = client.execute(request);
                System.out.println(response.toString());
            } catch (URISyntaxException e) {
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return response.toString();
        }
    }).start();

    runOnUiThread(new Runnable() {
            @Override
            public void run() {
// runs on the UI thread so update UI here
            }
        });