httprequest 中的空异常

Question

我正在尝试从mysql（xampp）数据库中获取值，但它不起作用我的数据库名称是meeting_planner，表名称是参与者

try {
                HttpPost httppost;
                HttpClient httpclient;
                httpclient = new DefaultHttpClient();
                httppost = new HttpPost(
                "http://10.10.10.159/my_folder_inside_htdocs/getdata.php");
                System.out.println("after url");
                ResponseHandler<String> responseHandler = new BasicResponseHandler();
                System.out.println("after response handler");
                 final String response = httpclient.execute(httppost,
                        responseHandler);


                 System.out.println("the response is "+response);
                 Log.e("pass 1", "connection success ");
            } catch (Exception e) {
                  e.printStackTrace();
            }

getdata.php代码在这里

<?php
     mysql_connect("localhost","admin","admin"); // host, username, password...
   mysql_select_db("meeting_planner"); // db name...

    $q=mysql_query("SELECT * FROM participant");
    while($row=mysql_fetch_assoc($q))
            $json_output[]=$row;
          print(json_encode($json_output));
    mysql_close();
?>

响应变量在 System.out.println（"response"+response） 的结果中为 null;日志猫在这里

android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145)
at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84)
at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
at libcore.io.IoBridge.connect(IoBridge.java:112)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459)
at java.net.Socket.connect(Socket.java:843)
at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
at 

org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection（DefaultClientConnectionOpera

托.java：144）

at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:653)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:627)
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:616)
at com.example.androidmeetingplanner.Invite.addListenerOnButton(Invite.java:130)
at com.example.androidmeetingplanner.Invite.onCreate(Invite.java:39)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)

Answer 1

您正在获得 NetworkOnMainThreadException。 请使用 AsyncTask 使 HttpRequest 如下所示：

    private class HttpGetter extends AsyncTask<Void, Void, Void> {
            @Override
            protected Void doInBackground(URL... urls) {
                try {
                    HttpClient httpclient = new DefaultHttpClient();
                    HttpPost httppost= new HttpPost(          "http://10.10.10.159/my_folder_inside_htdocs/getdata.php");
                    System.out.println("after url");
                    ResponseHandler<String> responseHandler = new BasicResponseHandler();
                    System.out.println("after response handler");
                    String response = httpclient.execute(httppost,responseHandler);
                    System.out.println("the response is "+response);
                    Log.e("pass 1", "connection success ");
            } catch (Exception e) {
              e.printStackTrace();
            }   
            return null; 
        }
}

并在您的活动中编写以下代码来执行它

    HttpGetter getter = new HttpGetter();
    getter.execute(null,null);

Answer 2

android.os.NetworkOnMainThreadException 说你在 GUI 线程中调用请求。您应该在另一个线程中使用网络执行所有操作。

例如，您可以将此代码添加到 AsyncTask 中。

Answer 3

请查看此参考资料： 如何修复android.os.NetworkOnMainThreadException？。Android 不能让你在主线程上发出 http 请求，你应该在不同的线程上发出请求