android - HttpHostConnectException + NullPointerException

Question

我正在尝试从我的计算机上的 mySQL 数据库获取数据。当我在模拟器上运行应用程序时，我得到一个 HttpHostConnectException (我已经在浏览器中测试了我的地址，并尝试了带或不带端口号的 10.0.2.2)，然后应用程序崩溃并出现 NullPointerException。我该如何解决这些问题？

连接器.java

public class Connector {

public JSONArray getResults(){

    String url = "http://192.168.87.1/android/getStudents.php";

    HttpEntity httpentity = null;

    try
    {
        DefaultHttpClient httpclient =new DefaultHttpClient();
        HttpGet httpget= new HttpGet(url);
        HttpResponse httpresponse = httpclient.execute(httpget);
        httpentity = httpresponse.getEntity();

    }catch (ClientProtocolException e){
        e.printStackTrace();

    }catch (IOException e){
        e.printStackTrace();
    }

    JSONArray jsonarray = null;
    if(httpentity != null){
        try{
            String entityresponse = EntityUtils.toString(httpentity);
            Log.e("Entity Response: ", entityresponse);

            jsonarray = new JSONArray(entityresponse);

        }catch (JSONException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }
    }
    return jsonarray;
}}

MainActivity.java

public class MainActivity extends ActionBarActivity {

private TextView resultsViewer;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    this.resultsViewer = (TextView)this.findViewById(R.id.resultsViewer);

    new getResultsTask().execute(new Connector());
}


private void setText (JSONArray jsonarray){

    String string = "";
    for(int i=0; i<jsonarray.length(); i++){
        JSONObject json = null;
        try{
            json = jsonarray.getJSONObject(i);

            string = string + "Exam : " + json.getString("exam_name") + "\n" +
                              "Score :" + json.getString("score") + "\n\n";

        }catch (JSONException e){
            e.printStackTrace();
        }
    }
    this.resultsViewer.setText(string);
}

private class getResultsTask extends AsyncTask<Connector, Long, JSONArray>{

    @Override
    protected JSONArray doInBackground(Connector... params) {

                 return params[0].getResults();
    }

    @Override
    protected void onPostExecute(JSONArray jsonarray) {

        setText(jsonarray);
    }

}}

来自 LogCat 的一些行

Converting to string: TypedValue{t=0x12/d=0x0 a=2 r=0x7f09003f}
 Emulator without GPU emulation detected.
 Background sticky concurrent mark sweep GC freed 3259(270KB) AllocSpace objects, 0(0B) LOS objects, 31% free, 759KB/1117KB, paused 3.009ms total 1.004s
 org.apache.http.conn.HttpHostConnectException: Connection to http://192.168.56.1 refused
 at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:188)

和 NullPointerException

    Shutting down VM
 --------- beginning of crash
 FATAL EXCEPTION: main
 Process: com.ed.jsontest2, PID: 1302
 java.lang.NullPointerException: Attempt to invoke virtual method 'int org.json.JSONArray.length()' on a null object reference
    at com.ed.jsontest2.MainActivity.setText(MainActivity.java:32)

Answer 1

如果服务器在您的本地计算机上运行，​​则必须使用 IP 地址 10.0.0.2。端口号是必需的

您的网址应该是http://10.0.2.2:portnumber/android/getStudents.php ...

端口号是你本地服务器运行的端口

如果您从远程计算机运行服务器，则替换主机 IP 地址