Question

I am trying to send a string from a android application to a servlet and then retrieve that string to my android application ,but when i try to invoke the servlet it force close on me
and i dont know why (im very new to android and this is a practice exercise for me)
here is my android simple app:

ANDROID

package com.theopentutorials.android;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class HttpGetServletActivity extends Activity implements OnClickListener { 
    Button button; 
    TextView outputText; 
    public static String request = "kjo ishte e gjitha"; 
    public static final String URL = ("http://10.0.2.2:8080/HttpGetServlet/HelloWorldServlet?param1=" + request); 

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.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();
        }

        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);
        }
    }
}

and here is my simple servlet

SERVLET

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/HelloWorldServlet")
public class HelloWorldServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public HelloWorldServlet() {
        super();
    }
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException, IOException {
        String par1 =  request.getParameter("param1");
        PrintWriter out = response.getWriter();
        out.println(par1);
    }
}

And the logcat log error says

01-10 13:36:50.014: E/AndroidRuntime(1187): FATAL EXCEPTION: AsyncTask #1
01-10 13:36:50.014: E/AndroidRuntime(1187): java.lang.RuntimeException: An error occured while executing doInBackground()
01-10 13:36:50.014: E/AndroidRuntime(1187):     at android.os.AsyncTask$3.done(AsyncTask.java:299)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.util.concurrent.FutureTask.run(FutureTask.java:239)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.lang.Thread.run(Thread.java:856)
01-10 13:36:50.014: E/AndroidRuntime(1187): Caused by: java.lang.NullPointerException: lock == null
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.io.Reader.<init>(Reader.java:64)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.io.InputStreamReader.<init>(InputStreamReader.java:122)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.io.InputStreamReader.<init>(InputStreamReader.java:59)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at com.theopentutorials.android.HttpGetServletActivity$GetXMLTask.getOutputFromUrl(HttpGetServletActivity.java:64)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at com.theopentutorials.android.HttpGetServletActivity$GetXMLTask.doInBackground(HttpGetServletActivity.java:54)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at com.theopentutorials.android.HttpGetServletActivity$GetXMLTask.doInBackground(HttpGetServletActivity.java:1)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
01-10 13:36:50.014: E/AndroidRuntime(1187):     at java.util.concurrent.FutureTask.run(FutureTask.java:234)
01-10 13:36:50.014: E/AndroidRuntime(1187):     ... 4 more

doest somebody have any idea ?
Thank you for your help in advance !
Have a nice day!

Answer 1

You need to add the internet access permission

<uses-permission android:name="android.permission.INTERNET"/>

I found that you should use the URLEncoder to encode the url because your url contains spaces. Please check http://developer.android.com/reference/java/net/URLEncoder.html