Async socket demo in java

EchoClient.java

package asyncsocket;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Steven
 */
public class EchoClient {
    
    public EchoClient( String host, int port, final String message, final AtomicInteger messageWritten, final AtomicInteger messageRead ) throws IOException {
        //create a socket channel
        AsynchronousSocketChannel sockChannel = AsynchronousSocketChannel.open();
        
        //try to connect to the server side
        sockChannel.connect( new InetSocketAddress(host, port), sockChannel, new CompletionHandler<Void, AsynchronousSocketChannel >() {
            @Override
            public void completed(Void result, AsynchronousSocketChannel channel ) {
                //start to read message
                startRead( channel,messageRead );
                
                //write an message to server side
                startWrite( channel, message, messageWritten );
            }

            @Override
            public void failed(Throwable exc, AsynchronousSocketChannel channel) {
                System.out.println( "fail to connect to server");
            }
            
        });
    }
   
    private void startRead( final AsynchronousSocketChannel sockChannel, final AtomicInteger messageRead ) {
        final ByteBuffer buf = ByteBuffer.allocate(2048);
        
        sockChannel.read( buf, sockChannel, new CompletionHandler<Integer, AsynchronousSocketChannel>(){

            @Override
            public void completed(Integer result, AsynchronousSocketChannel channel) {   
                //message is read from server
                messageRead.getAndIncrement();
                
                //print the message
                System.out.println( "Read message:" + new String( buf.array()) );
            }

            @Override
            public void failed(Throwable exc, AsynchronousSocketChannel channel) {
                System.out.println( "fail to read message from server");
            }
            
        });
        
    }
    private void startWrite( final AsynchronousSocketChannel sockChannel, final String message, final AtomicInteger messageWritten ) {
        ByteBuffer buf = ByteBuffer.allocate(2048);
        buf.put(message.getBytes());
        buf.flip();
        messageWritten.getAndIncrement();
        sockChannel.write(buf, sockChannel, new CompletionHandler<Integer, AsynchronousSocketChannel >() {
            @Override
            public void completed(Integer result, AsynchronousSocketChannel channel ) {
                //after message written
                //NOTHING TO DO
            }

            @Override
            public void failed(Throwable exc, AsynchronousSocketChannel channel) {
                System.out.println( "Fail to write the message to server");
            }
        });
    }
    
    public static void main( String...args ) {
        try {
            AtomicInteger messageWritten = new AtomicInteger( 0 );
            AtomicInteger messageRead = new AtomicInteger( 0 );
            
            for( int i = 0; i < 1000; i++ ) {
                new EchoClient( "127.0.0.1", 3575, "echo test", messageWritten, messageRead );
            }
            
            while( messageRead.get() != 1000 ) {
                Thread.sleep( 1000 );
                System.out.println( "message write:" + messageWritten );
                System.out.println( "message read:" + messageRead );
            }
        } catch (Exception ex) {
            Logger.getLogger(EchoClient.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    
}

EchoServer.java

package asyncsocket;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Steven Ou
 */
public class EchoServer {
    
    public EchoServer( String bindAddr, int bindPort ) throws IOException {
        InetSocketAddress sockAddr = new InetSocketAddress(bindAddr, bindPort);
        
        //create a socket channel and bind to local bind address
        AsynchronousServerSocketChannel serverSock =  AsynchronousServerSocketChannel.open().bind(sockAddr);
        
       //start to accept the connection from client
        serverSock.accept(serverSock, new CompletionHandler<AsynchronousSocketChannel,AsynchronousServerSocketChannel >() {

            @Override
            public void completed(AsynchronousSocketChannel sockChannel, AsynchronousServerSocketChannel serverSock ) {
                //a connection is accepted, start to accept next connection
                serverSock.accept( serverSock, this );
                //start to read message from the client
                startRead( sockChannel );
                
            }

            @Override
            public void failed(Throwable exc, AsynchronousServerSocketChannel serverSock) {
                System.out.println( "fail to accept a connection");
            }
            
        } );
        
    }
    
    private void startRead( AsynchronousSocketChannel sockChannel ) {
        final ByteBuffer buf = ByteBuffer.allocate(2048);
        
        //read message from client
        sockChannel.read( buf, sockChannel, new CompletionHandler<Integer, AsynchronousSocketChannel >() {

            /**
             * some message is read from client, this callback will be called
             */
            @Override
            public void completed(Integer result, AsynchronousSocketChannel channel  ) {
                buf.flip();
                
                // echo the message
                startWrite( channel, buf );
                
                //start to read next message again
                startRead( channel );
            }

            @Override
            public void failed(Throwable exc, AsynchronousSocketChannel channel ) {
                System.out.println( "fail to read message from client");
            }
        });
    }
    
     private void startWrite( AsynchronousSocketChannel sockChannel, final ByteBuffer buf) {
         sockChannel.write(buf, sockChannel, new CompletionHandler<Integer, AsynchronousSocketChannel >() {

             @Override
             public void completed(Integer result, AsynchronousSocketChannel channel) {                 
                 //finish to write message to client, nothing to do
             }

             @Override
             public void failed(Throwable exc, AsynchronousSocketChannel channel) {
                 //fail to write message to client
                 System.out.println( "Fail to write message to client");
             }
             
         });
     }
     
     public static void main( String[] args ) {
        try {
            new EchoServer( "127.0.0.1", 3575 );
            for( ; ; ) {
                Thread.sleep(10*1000);
            }
        } catch (Exception ex) {
            Logger.getLogger(EchoServer.class.getName()).log(Level.SEVERE, null, ex);
        }
     }
}

With the EchoServer.java, when a user disconnects it causes a huge spike in CPU % and memory. Unsure as to why this occurs as it should just go back to the accept state right?

Then the client disconnect the: public void completed(Integer result, AsynchronousSocketChannel channel ) will be fired in a loop and increase CPU and memory.

If the Integer result be -1, it means of the client is disconnected, so you can force the close connection:

@Override
            public void completed(Integer result, AsynchronousSocketChannel channel  ) {
                buf.flip();

                if(result == -1){
                    try {
                        System.out.println("Client disconnected");
                        channel.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    return;
                }

                // echo the message
                startWrite( channel, buf );

                //start to read next message again
                startRead( channel );
            }