服务端接收消息 xxx ，服务端回应 response: xxx 

EchoServer.java
AcceptHandler.java
ReadHandler.java 
WriteHandler.java 


EchoServer.java

import java.net.InetSocketAddress;
import java.nio.channels.AsynchronousServerSocketChannel;

public class EchoServer {
    static final int PORT = 8889;
    public static void main(String args[]) throws Exception {
        final AsynchronousServerSocketChannel serverSocketChannel = AsynchronousServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(PORT));
        serverSocketChannel.accept(null,new AcceptHandler());
        System.out.println("EchoServer bind done,port="+PORT);
        Thread.sleep(100000000);
    }
}


AcceptHandler.java 


import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;

public class AcceptHandler implements CompletionHandler< AsynchronousSocketChannel, Void> {
    // 256
    static final int MAX_SIZE = 8;
    @Override
    public void completed(AsynchronousSocketChannel asynchronousSocketChannel, Void attachment) {
        try {
            System.out.println("connected from: " + asynchronousSocketChannel.getRemoteAddress());
        } catch (IOException e) {
            e.printStackTrace();
        }
        //  字节缓冲区大小 8  ， 0123456789 会读取2次
        ByteBuffer buffer = ByteBuffer.allocate(MAX_SIZE);
        asynchronousSocketChannel.read(buffer, buffer, new ReadHandler(asynchronousSocketChannel));
    }

    @Override
    public void failed(Throwable throwable, Void attachment) {
        System.out.println("AcceptHandler.failed,"+throwable);
        throwable.printStackTrace();
    }
}


ReadHandler.java 


import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.nio.charset.Charset;

public class ReadHandler implements CompletionHandler< Integer, ByteBuffer> {
    static final Charset charSet = Charset.forName("UTF-8");
    private final AsynchronousSocketChannel channel;

    public ReadHandler(AsynchronousSocketChannel channel) {
        this.channel = channel;
    }

    @Override
    public void completed(Integer intResult, ByteBuffer byteBuffer) {
        System.out.println("read-handler-"+Thread.currentThread());
        byteBuffer.flip();
        int remaining = byteBuffer.remaining();
        System.out.println("intResult=" + intResult+",remaining="+remaining);
        byte[] message = new byte[remaining];
        byteBuffer.get(message);

        String data = new String(message, charSet);
        System.out.println("received: " + data);
        String response = "response:" + data;
        doWrite(response);
    }

    @Override
    public void failed(Throwable throwable, ByteBuffer byteBuffer) {
        System.out.println("ReaderHandler.failed,"+throwable);
        try {
            channel.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    private void doWrite(String result) {
        System.out.println("send back: " + result);
        byte[] bytes = result.getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
        writeBuffer.put(bytes);
        writeBuffer.flip();
        channel.write(writeBuffer, writeBuffer, new WriteHandler(channel));
    }
}



WriteHandler.java 


import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;

public class WriteHandler implements CompletionHandler< Integer, ByteBuffer> {

    private final AsynchronousSocketChannel channel;

    public WriteHandler(final AsynchronousSocketChannel channel) {
        this.channel = channel;
    }

    @Override
    public void completed(Integer result, ByteBuffer buffer) {
        System.out.println("write-hanlder-"+Thread.currentThread());
        // 没有发送完，就继续发送直到完成
        if (buffer.hasRemaining()) {
            channel.write(buffer, buffer, this);
        } else {
            // 写完成 继续读取 
            // 创建新的Buffer 用于读取
            // 1024 8
            ByteBuffer readBuffer = ByteBuffer.allocate(8);
            channel.read(readBuffer, readBuffer, new ReadHandler(channel));
        }
    }
    @Override
    public void failed(Throwable exc, ByteBuffer attachment) {
        System.out.println("WriterHandler.failed,"+exc);
        try {
            channel.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}



测试 

telnet 127.0.0.1 8889
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
1
response:1
2
response:2
123456789
response:12345678response:9
3
response:3
4
response:4
5
response:5
6
response:6
123456789abcd
response:12345678response:9abcd
7
response:7


https://gitee.com/dyyx/work2024/tree/master/demo/aiodemo/src/main/java/demo/echo2