无法从Android连接到Servlet

Question

我有一个Android应用程序和一个Servlet。现在我想向Servlet发送一个帖子，但是我遇到了运行时异常，无法连接到Servlet。我想建立一个从应用程序到servlet的连接，以最终发送一些数据。我现在有一个示例，但它无法连接。

Android

public class HttpGetServletActivity extends Activity implements
        OnClickListener {
    Button button;
    TextView outputText;

    public static final String URL =
            "http://10.0.6.169:1234/HttpGetServlet/HelloWorldServlet";

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViewsById();

        button.setOnClickListener(this);
    }

    private void findViewsById() {
        button = (Button) findViewById(R.id.button);
        outputText = (TextView) findViewById(R.id.outputTxt);
    }

    public void onClick(View view) {
        GetXMLTask task = new GetXMLTask();
        task.execute(new String[] { URL });
    }

    private class GetXMLTask extends AsyncTask<String, Void, String> {
        @Override
        protected String doInBackground(String... urls) {
            String output = null;
            for (String url : urls) {
                output = getOutputFromUrl(url);
            }
            return output;
        }

        private String getOutputFromUrl(String url) {
            StringBuffer output = new StringBuffer("");
            try {
                InputStream stream = getHttpConnection(url);
                BufferedReader buffer = new BufferedReader(
                        new InputStreamReader(stream));
                String s = "";
                while ((s = buffer.readLine()) != null)
                    output.append(s);
            } catch (IOException e1) {
                e1.printStackTrace();
            }
            return output.toString();
        }

        // Makes HttpURLConnection and returns InputStream
        private InputStream getHttpConnection(String urlString)
                throws IOException {
            InputStream stream = null;
            URL url = new URL(urlString);
            URLConnection connection = url.openConnection();

            try {
                HttpURLConnection httpConnection = (HttpURLConnection) connection;
                httpConnection.setRequestMethod("GET");
                httpConnection.connect();

                if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                    stream = httpConnection.getInputStream();
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
            return stream;
        }

        @Override
        protected void onPostExecute(String output) {
            outputText.setText(output);
        }
    }
}

Servlet

public class HelloWorldServlet extends HttpServlet {
   // private static final long serialVersionUID = 1L;

    public HelloWorldServlet() {
        super();
    }

    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        out.println("Hello Android !!!!");
    }
}

运行时异常 这是我在Android Studio中得到的例外情况

   java.lang.RuntimeException: An error occurred while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:354)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
        at java.util.concurrent.FutureTask.run(FutureTask.java:271)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:764)
     Caused by: java.lang.NullPointerException
        at java.io.Reader.<init>(Reader.java:78)
        at java.io.InputStreamReader.<init>(InputStreamReader.java:72)
        at com.ict.simplehttpgetservlet.HttpGetServletActivity$GetXMLTask.getOutputFromUrl(HttpGetServletActivity.java:61)
        at com.ict.simplehttpgetservlet.HttpGetServletActivity$GetXMLTask.doInBackground(HttpGetServletActivity.java:52)
        at com.ict.simplehttpgetservlet.HttpGetServletActivity$GetXMLTask.doInBackground(HttpGetServletActivity.java:47)
        at android.os.AsyncTask$2.call(AsyncTask.java:333)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245) 
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) 
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641) 
        at java.lang.Thread.run(Thread.java:764)