使用 NIO 实现 echo 服务器

NIO相关知识点

IO、NIO、AIO 内部原理分析
NIO 之 Selector实现原理
NIO 之 Channel实现原理
NIO 之 ByteBuffer实现原理

服务器使用NIO来实现一个echo协议的服务器。
echo协议简单也很有用，可以测试网络连接。

消息的格式为：消息长度（int）+消息内容

通过消息长度来进行socket分包，防止读取出现半包、粘包等问题。

服务端

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;

public class NioEchoServer {

    public static void server() {
        ServerSocketChannel ssc = null;
        Selector selector = null;
        try {
            ssc = ServerSocketChannel.open();
            //设置为非阻塞
            ssc.configureBlocking(false);
            ssc.bind(new InetSocketAddress(9000), 10);
            selector = Selector.open();
            ssc.register(selector, SelectionKey.OP_ACCEPT);
        } catch (IOException e) {
            e.printStackTrace();
        }

        while (true) {
            try {
                selector.select();
            } catch (IOException e) {
                e.printStackTrace();
            }

            try {
                Set set = selector.selectedKeys();
                Iterator it = set.iterator();
                while (it.hasNext()) {
                    SelectionKey key = it.next();
                    set.remove(key);
                    try {
                        if (key.isAcceptable()) {
                            ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();
                            SocketChannel clientChannel = serverChannel.accept();
                            clientChannel.configureBlocking(false);
                            MessageInfo messageInfo = new MessageInfo();
                            clientChannel.register(selector, SelectionKey.OP_READ, messageInfo);
                        } else if (key.isReadable()) {
                            SocketChannel clientChannel = (SocketChannel) key.channel();
                            MessageInfo messageInfo = (MessageInfo)key.attachment();
                            
                            if(messageInfo.getLenBuf() == null){
                                messageInfo.setLenBuf(ByteBuffer.allocate(4));
                            }
                            
                            //消息长度
                            int len = messageInfo.getLen();
                            //判断消息长度是否读取完成
                            if(len!=-1){
                                if(messageInfo.contentBuf == null){
                                    //创建指定消息长度的buf
                                    messageInfo.contentBuf = ByteBuffer.allocate(len);
                                }
                                //如果消息未读取完成，继续读取
                                if(messageInfo.contentBuf.position()

客户端

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;

public class NioEchoClient {

    public static void main(String[] args) {
        
        SocketAddress sa = new InetSocketAddress("127.0.0.1", 9000);
        try {
            SocketChannel client = SocketChannel.open(sa);
            
            byte[] data = "大家好".getBytes();
            ByteBuffer lenBuf = ByteBuffer.wrap(int2byte(data.length));
            ByteBuffer textBuf = ByteBuffer.wrap(data);
            ByteBuffer[] bufArray = new ByteBuffer[]{lenBuf, textBuf};
            client.write(bufArray);
            
            lenBuf.clear();
            textBuf.clear();
            client.read(bufArray);
            
            System.out.println("echo:"+new String(textBuf.array()));
            client.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        
    }
    
    /**
     * int 转 byte[] 数组
     * @param len
     * @return
     */
    public static byte[] int2byte(int len) {
        byte[] b = new byte[4];
        b[0] = (byte) (len >> 24);
        b[1] = (byte) (len >> 16 & 0XFF);
        b[2] = (byte) (len >> 8 & 0XFF);
        b[3] = (byte) (len & 0XFF);
        return b;
    }
}

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