HttpServlet Receive Null in doPost() from Android Client

Question

I am trying to send some data from Android Client to HttpServlet. My Servlet code is as follows

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class DBServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
Connection connection= null;   

/**
 * @see HttpServlet#HttpServlet()
 */
public DBServlet() {
        super();
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response) 
        throws ServletException, IOException {

    doPost(request, response);
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {

    if(request.getParameterNames().hasMoreElements()){
                insertRecord(request, getDbConnection());
            }
            else{ System.out.println("Servlet Started First Time"); }



}

/**
 * Return database connection
 * @return
 */
private Connection getDbConnection(){
        String connectionURL = "jdbc:mysql://127.0.0.1:3306/testDB";

        try {

            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(connectionURL, "root", "");

        } catch (SQLException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return connection;  
}

/**
 * Insert record in database
 * @param request
 * @param connection
 */
private void insertRecord(HttpServletRequest request, Connection connection){   

            System.out.println("===== Received Record =====");

            PreparedStatement stmt;

            try {
                stmt = connection.prepareStatement("insert into users(Name,email,password) values(?,?,?)");
                stmt.setString(1, request.getParameter("name"));
                stmt.setString(2, request.getParameter("e-mail"));
                stmt.setString(3, request.getParameter("password"));

                int i= stmt.executeUpdate();

                if(i != 0){
                    System.out.println("data inserted !!!");
                }
                else{
                    System.out.println("data failed to insert");
                }

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

            finally{

                try {
                    connection.close();
                } catch (SQLException e) {

                    e.printStackTrace();
                }
            }
    }
}

and my android code is

import java.io.DataOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;

import org.apache.http.NameValuePair;

import org.apache.http.message.BasicNameValuePair;

import com.example.messenger.R;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class SignUp extends Activity {

Button register;

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

    register = (Button)findViewById(R.id.register);

    register.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Log.v("OnClick", "=== onClick ===");
            registerUser();

        }
    });
}

@SuppressLint({ "NewApi", "NewApi", "NewApi" })
private void registerUser(){


        String name= ((EditText)findViewById(R.id.name)).getText().toString();
        String email= ((EditText)findViewById(R.id.email)).getText().toString();
        String password= ((EditText)findViewById(R.id.password)).getText().toString();

        ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
        nameValuePairs.add(new BasicNameValuePair("name", name));
        nameValuePairs.add(new BasicNameValuePair("email", email));
        nameValuePairs.add(new BasicNameValuePair("password", password));


        try {

            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);

            URL url=new URL("http://192.168.1.10:8080/DBservlet/DBServlet");
            HttpURLConnection con = (HttpURLConnection)url.openConnection();
            con.setDoOutput(true);
            con.setRequestMethod("POST");
            DataOutputStream dos=new DataOutputStream(con.getOutputStream());
            dos.writeBytes(name);
            dos.flush();
            dos.close();

}  catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

}

}

The problem is that when I run the 'Servlet' I get output 'Servlet Started First Time' which is OK but when I run my android client and write some data in EditText fields and press register button nothing happens. 'Servlet' receive nothing. Please let me know how can I solve this problem.

Regards,

Answer 1

Your servlet looks functionally okay (design-technically not, but that's a different matter). Your Android side looks however definitely not good.

This,

ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("name", name));
nameValuePairs.add(new BasicNameValuePair("email", email));
nameValuePairs.add(new BasicNameValuePair("password", password));

is how you would be preparing request parameters before sending the HTTP request using the Android-builtin Apache HttpClient API.

But here,

URL url=new URL("http://192.168.1.10:8080/DBservlet/DBServlet");
HttpURLConnection con = (HttpURLConnection)url.openConnection();
con.setDoOutput(true);
con.setRequestMethod("POST");
DataOutputStream dos=new DataOutputStream(con.getOutputStream());
dos.writeBytes(name);
dos.flush();
dos.close();

you're however sending the HTTP request using the Java SE builtin URLConnection API instead. And then actually in a bad way; you're not sending a proper application/x-www-form-urlendocded query string, but instead a single string value in the platform default encoding. Also the DataOutputStream makes completely no sense in this context, you're not creating a .dat file at all. This feels too much like a "roseindia.net-snippet". If you were indeed reading that terrible site, please put it in a lifetime blacklist from now on.

It look like that you're mixing different approaches of sending a HTTP POST request in Android.

1. Using HttpClient API
2. Using URLConnection API

You should choose the one or the other and stick to it. The above links point to concrete examples in flavor of a Stack Overflow answer.