Java Client Socket Connection in Android

android sockets networking ip client

20,157

In your application the NetworkOnMainThreadException is occurred. From the doc you ca see that

The exception that is thrown when an application attempts to perform a networking operation on its main thread.

So you have to call your RunSocketClient method from another thread rather than the main thread. Use a handler or asynctask or different thread to perform this operation.

To know about good designing you can see this link

http://developer.android.com/training/articles/perf-anr.html

20,157

Author by

aagarwal

Updated on May 23, 2020

Comments

aagarwal almost 4 years

I am creating a client socket connection between my computer and android.

Here is the code for the server:

import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;


class Server {
  public static void main(String[] args) {
    String ip = getIpAddress();

    if (ip != "false") {
        try {
            ServerSocket srvr = new ServerSocket(4444);

        Socket client = null;
        try {
            client = srvr.accept();

            PrintWriter out = new PrintWriter(client.getOutputStream(), true);
            System.out.print("Sending ip address: '" + ip + "'\n");
            out.print(ip);
            out.close();
            client.close();
            srvr.close();
        } catch(Exception e) {
            System.out.print(String.format("Accept failed: %s",e));
        }
        } catch (Exception e) {
            System.out.print(String.format("Could not listem on port: %s",e));
        }
    }
    else
    {
        System.out.print("Could not get ip address");
    }
  }

  public static String getIpAddress() {
    InetAddress host;
    String ipString = "false";

    try {
        host = InetAddress.getLocalHost();
        ipString = host.getHostAddress();
    } catch (UnknownHostException e) {
        System.out.println(e);
    }

    return ipString;
  }
}

When I run the client on the computer everything works. Here is the code for the computer client:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;


public class Client {
  public static void main(String[] args) {
    System.out.print(RunSocketClient());
  }

  public static String RunSocketClient() {
    try {
        Socket clnt = new Socket("localhost",4444);
        BufferedReader in = new BufferedReader(new InputStreamReader(clnt.getInputStream()));

        String fromServer;
        fromServer = in.readLine();

        return fromServer;
    } catch (IOException e) {
        return "nothing";
    }
  }
}

When I run the this client code in android the system stops working, what is the error? Here is the android client code:

package com.example.clientapp;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.LinearLayout;
import android.widget.TextView;

public class MainActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    LinearLayout lView = new LinearLayout(this);

    TextView myText = new TextView(this);
    String ip = RunSocketClient();
    Log.d("ClientApp",ip);
    myText.setText(ip);

    lView.addView(myText);

    setContentView(lView);
  }

  public static String RunSocketClient() {
    try {
        Socket clnt = new Socket("localhost",4444);
        BufferedReader in = new BufferedReader(new InputStreamReader(clnt.getInputStream()));

        String fromServer;
        fromServer = in.readLine();

        return fromServer;
    } catch (IOException e) {
        return "nothing";
    }
  }
}

Here is the logcat of the application crash:

04-13 00:10:31.411: D/AndroidRuntime(13978): Shutting down VM

04-13 00:10:31.411: W/dalvikvm(13978): threadid=1: thread exiting with uncaught exception (group=0x410ab300)

04-13 00:10:31.411: E/AndroidRuntime(13978): FATAL EXCEPTION: main

04-13 00:10:31.411: E/AndroidRuntime(13978): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.clientapp/com.example.clientapp.MainActivity}: android.os.NetworkOnMainThreadException

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.ActivityThread.access$600(ActivityThread.java:130)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.os.Handler.dispatchMessage(Handler.java:99)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.os.Looper.loop(Looper.java:137)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.ActivityThread.main(ActivityThread.java:4745)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.lang.reflect.Method.invokeNative(Native Method)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.lang.reflect.Method.invoke(Method.java:511)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at dalvik.system.NativeStart.main(Native Method)

04-13 00:10:31.411: E/AndroidRuntime(13978): Caused by: android.os.NetworkOnMainThreadException

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.net.InetAddress.lookupHostByName(InetAddress.java:385)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.net.InetAddress.getAllByName(InetAddress.java:214)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.net.Socket.tryAllAddresses(Socket.java:108)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.net.Socket.<init>(Socket.java:177)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at java.net.Socket.<init>(Socket.java:149)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at com.example.clientapp.MainActivity.RunSocketClient(MainActivity.java:34)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at com.example.clientapp.MainActivity.onCreate(MainActivity.java:23)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.Activity.performCreate(Activity.java:5008)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)

04-13 00:10:31.411: E/AndroidRuntime(13978):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)

04-13 00:10:31.411: E/AndroidRuntime(13978):    ... 11 more