How to compile this network socket example in Java using Eclipse?

Question

Okay, I found this example in the book, so I know that this code is error free. The program below contains two classes, both of them are main classes. One is for client and one is for server.

According to the book, I'm supposed to compile them like this:

Compile client and server and then start server as follows:

$ java GreetingServer 6066 Waiting for client on port 6066...

Check client program as follows:

$ java GreetingClient localhost 6066 Connecting to localhost on port 6066 Just connected to localhost/127.0.0.1:6066 Server says Thank you for connecting to /127.0.0.1:6066 Goodbye!

I want to be able to run them on eclipse, but every time I do so, it's giving me this error: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at GreetingServer.main(GreetingServer.java:47).

HOW CAN I RUN THIS PROGRAM IN ECLIPSE? Thanks.

// File Name GreetingClient.java

import java.net.*;
import java.io.*;

public class GreetingClient
{
   public static void main(String [] args)
   {
      String serverName = args[0];
      int port = Integer.parseInt(args[1]);
      try
      {
         System.out.println("Connecting to " + serverName
                             + " on port " + port);
         Socket client = new Socket(serverName, port);
         System.out.println("Just connected to "
                      + client.getRemoteSocketAddress());
         OutputStream outToServer = client.getOutputStream();
         DataOutputStream out =
                       new DataOutputStream(outToServer);

         out.writeUTF("Hello from "
                      + client.getLocalSocketAddress());
         InputStream inFromServer = client.getInputStream();
         DataInputStream in =
                        new DataInputStream(inFromServer);
         System.out.println("Server says " + in.readUTF());
         client.close();
      }catch(IOException e)
      {
         e.printStackTrace();
      }
   }
}


// File Name GreetingServer.java

import java.net.*;
import java.io.*;

public class GreetingServer extends Thread
{
   private ServerSocket serverSocket;

   public GreetingServer(int port) throws IOException
   {
      serverSocket = new ServerSocket(port);
      serverSocket.setSoTimeout(10000);
   }

   public void run()
   {
      while(true)
      {
         try
         {
            System.out.println("Waiting for client on port " +
            serverSocket.getLocalPort() + "...");
            Socket server = serverSocket.accept();
            System.out.println("Just connected to "
                  + server.getRemoteSocketAddress());
            DataInputStream in =
                  new DataInputStream(server.getInputStream());
            System.out.println(in.readUTF());
            DataOutputStream out =
                 new DataOutputStream(server.getOutputStream());
            out.writeUTF("Thank you for connecting to "
              + server.getLocalSocketAddress() + "\nGoodbye!");
            server.close();
         }catch(SocketTimeoutException s)
         {
            System.out.println("Socket timed out!");
            break;
         }catch(IOException e)
         {
            e.printStackTrace();
            break;
         }
      }
   }
   public static void main(String [] args)
   {
      int port = Integer.parseInt(args[0]);
      try
      {
         Thread t = new GreetingServer(port);
         t.start();
      }catch(IOException e)
      {
         e.printStackTrace();
      }
   }
}

Answer 1

See these lines

public static void main(String [] args)
{
  String serverName = args[0]; //<-- Expecting a value
  int port = Integer.parseInt(args[1]); //<-- Expecting a value

The args[] is a string array containing arguments that you pass via command line. And when you try to run it from eclipse directly, you arent specifying these values which results in args[] to be an empty array and thus args[0] gives an ArrayIndexOutOfBoundsException

To solve this, either create a run configuration from within eclipse (see screenshot)

and specify arguements that you want eclipse to pass when running this class. YOu can do this by right-clicking the project, select run, then run-configurations --> double click on java_application and pass in the information that you want. You may need to specify the main class name when specifying arguments so that eclipse can recognize which main class to pass args to.

OR you can just hardcode these values directly in the class itself (for testing)