我正在尝试从我机器上的 mySQL 数据库中获取数据。当我在模拟器上朗姆应用程序时，我得到一个HttpHostConnectException（我在浏览器中测试了我的地址并尝试了 10.0.2.2 有和没有端口号）然后应用程序崩溃了NullPointerException。我能做些什么来解决这些问题？
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 NullPointerExeption
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)