Android客户端应用程序无法连接到Java PC服务器 - 无路由到主机错误

Question

I'm building an app for Android that will communicate with a PC and exchange data. I've been mainly going through several examples in learning how to make apps and how to use Java sockets. One example that I have been trying to get to work is:

http://lakjeewa.blogspot.com/2014/05/simple-android-client-server-application.html

I've modified a few things from the code above (names of variables and key press functions) and when I use the IP Address: 10.0.2.2, and run the app in an emulator and the server on a desktop connected to a private network, the app and server works. I'm able to send a message from the app on the emulator to the server and the server receives it.

However when I run the server on a laptop and the client app on an android phone that are both wirelessly connected to another private network, I get an error in the android studio console saying " No route to host ." I went into my laptops command terminal and was able to ping my phone. And I've replaced the area of the code with the correct IPv4 Address and socket. I've also connected my laptop and phone to another wireless network and still cannot establish a connection.

What could be the issue? Is there something I must specify in the code to enable connections? Or do I have to do something with the network or hardware devices to establish the connection?

Please note: Code for activity, manifest and layout is basically the same as shown in the link, except for variable name changes and I removed the function: public boolean onCreateOptionsMenu(Menu menu)

Thank you for your help!

EDIT 2 Below is my source code for the android client:

    import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;

import android.app.Activity;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {
    private Socket client;
    private PrintWriter printwriter;
    private EditText textField;
    private Button button;
    private String messsage;

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

        textField = (EditText) findViewById(R.id.editText1); // reference to the text field
        button = (Button) findViewById(R.id.button1); // reference to the send button

        // Button press event listener
        button.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                messsage = textField.getText().toString(); // get the text message on the text field
                textField.setText(""); // Reset the text field to blank
                SendMessage sendMessageTask = new SendMessage();
                sendMessageTask.execute();
            }
        });
    }

    private class SendMessage extends AsyncTask<Void, Void, Void> {

        @Override
        protected Void doInBackground(Void... params) {
            try {

                client = new Socket("192.168.1.37", 4444); // connect to the server
                printwriter = new PrintWriter(client.getOutputStream(), true);
                printwriter.write(messsage); // write the message to output stream

                printwriter.flush();
                printwriter.close();
                client.close(); // closing the connection

            } catch (UnknownHostException e) {
                Context context = getApplicationContext();
                /* If I try to send a toast notification my app crashes
                String text = "Could not connect";
                int duration = Toast.LENGTH_SHORT;
                Toast notify = Toast.makeText(context, text, duration);
                notify.show();*/
                e.printStackTrace();
            } catch (IOException e) {
                Context context = getApplicationContext();
                /*String text = "Could not connect";
                int duration = Toast.LENGTH_SHORT;
                Toast notify = Toast.makeText(context, text, duration);
                notify.show();*/
                e.printStackTrace();
            }
            return null;
        }

    }
}

Source code for the server:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author alexc
 */
public class JavaServer {

    private static ServerSocket serverSocket;
    private static Socket clientSocket;
    private static InputStreamReader inputStreamReader;
    private static BufferedReader bufferedReader;
    private static String message;

    public static void main(String[] args) throws IOException {
        try {
            serverSocket = new ServerSocket(4444); // Server socket

        } catch (IOException e) {
            System.out.println("Could not listen on port: 4444");
        }

        System.out.println("Server started. Listening to the port 4444");
                int count = 0;
        while (count < 1000) {
                    count++;
            try {

                clientSocket = serverSocket.accept(); // accept the client connection
                inputStreamReader = new InputStreamReader(clientSocket.getInputStream());
                bufferedReader = new BufferedReader(inputStreamReader); // get the client message
                message = bufferedReader.readLine();

                System.out.println(message);
                inputStreamReader.close();
                clientSocket.close();

            } catch (IOException ex) {
                System.out.println("Problem in message reading");
            }
        }
                serverSocket.close();
    }

}

Answer 1

Hey y'all so I got my friend's router which is a Linksys E1000 Wireless-N router from Cisco and tested my android app and Java server and it works. Don't know what the exact configurations are but this what I did:

1. Enable DHCP on the router, otherwise you will have to set static IP Addresses on your PC and Android Phone

2. Make sure your PC and Android Phone are enabled to be discoverable on the network. I just remembered on my PC when I connected to this router, it asked me do I want to be able to be discovered on the network

3. Turn off firewall (and antivirus), or keep the port open you want all your connections for your android app to go through.

If you still have issues, here are some general troubleshooting tips (as whatever devices you use will vary):

• If you are not getting assigned IP addresses for your PC or android Phone and DHCP is enabled, try resetting the router (turning it off and on again; or full system reset)

• For windows, open command prompt and type ipconfig and find your IPv4 address. Make sure that you type the address in correctly. Then in the commmand prompt type ping 'android phone's IP Address' For example:

  ping 192.168.1.121

If you get a response that means your phone is on the network.

• For Android phones, download this app: https://play.google.com/store/apps/details?id=ua.com.streamsoft.pingtools&hl=en

Then try to ping the IPv4 address you found for ipconfig if your phone can ping it, then you are all good. If you can't ping it, try turning off the firewall and antivirus.

Anyway thank you all for the help and suggestions. Hope these suggestions help.