NIO网络编程原理与实战

1、NIO总览

下载思维导图

2、用NIO实现一个简易聊天室

本例是使用Java NIO实现一个简易聊天室功能，全部代码见下文。
实现NIO的七个步骤已在代码中注释，这是重点，请细读代码。

2.1 服务端

服务端 -> NIOServer.java:

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


/**
 * @author Administrator
 * @date 2021/4/9
 * NIO服务器端
 */
public class NIOServer {
    
    
    public static void main(String[] args) throws IOException {
    
    
        new NIOServer().start();
    }

    /**
     * 启动
     */
    public void start() throws IOException {
    
    
        // 1、创建Selector
        Selector selector = Selector.open();
        // 2、通过ServerSocketChannel创建channel通道
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        // 3、为channel通道绑定监听端口
        serverSocketChannel.bind(new InetSocketAddress(8000));
        // 4、设置channel为非阻塞模式
        serverSocketChannel.configureBlocking(false);
        // 5、将channel注册到selector上，监听连接事件
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("服务器已启动");
        // 6、循环等待新接入的连接
        for (; ; ) {
    
    
            int readyChannels = selector.select();
            if (readyChannels == 0) {
    
    
                continue;
            }

            // 获取可用channel集合
            Set<SelectionKey> selectionKeys = selector.selectedKeys();
            Iterator iterator = selectionKeys.iterator();
            while (iterator.hasNext()) {
    
    
                // selectionKey实例
                SelectionKey selectionKey = (SelectionKey) iterator.next();
                // 重要：移除Set中大的当前selectionKey
                iterator.remove();

                // 7、根据就绪状态，调用对应的业务处理逻辑。分接入事件和可读事件
                if (selectionKey.isAcceptable()) {
    
    
                    acceptHandler(serverSocketChannel, selector);
                }
                if (selectionKey.isReadable()) {
    
    
                    readHandler(selectionKey, selector);
                }
            }
        }
    }

    /**
     * 接入事件处理器
     */
    private void acceptHandler(ServerSocketChannel serverSocketChannel, Selector selector) throws IOException {
    
    
        // 创建socketChannel
        SocketChannel socketChannel = serverSocketChannel.accept();
        // 将socketChannel设置为非阻塞模式
        socketChannel.configureBlocking(false);
        // 将channel注册到selector上，监听可读事件
        socketChannel.register(selector, SelectionKey.OP_READ);
        // 回复客户端提示信息
        socketChannel.write(Charset.forName("UTF-8").encode("你与聊天室其他人不是朋友关系，请注意隐私安全"));
    }

    /**
     * 可读事件处理器
     */
    private void readHandler(SelectionKey selectionKey, Selector selector) throws IOException {
    
    
        // 要从selectionKey中获取到已经就绪的channel
        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
        // 创建buffer
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        // 循环读取客户端请求信息
        String request = "";
        while (socketChannel.read(byteBuffer) > 0) {
    
    
            // 切换buffer为读模式
            byteBuffer.flip();
            // 读取buffer中的内容
            request += Charset.forName("UTF-8").decode(byteBuffer);
        }

        // 将channel再次注册到selector上，监听它的可读事件
        socketChannel.register(selector, SelectionKey.OP_READ);
        // 将客户端发送的请求信息，广播给其他客户端
        if (request.length() > 0) {
    
    
            broadCast(selector, socketChannel, request);
        }
    }

    /**
     * 广播给其他客户端
     */
    private void broadCast(Selector selector, SocketChannel sourceSocketChannel, String request) {
    
    
        // 获取所有已接入的客户端channel
        Set<SelectionKey> selectionKeySet = selector.keys();
        // 循环向所有的channel广播信息
        selectionKeySet.forEach(selectionKey -> {
    
    
            Channel targetChannel = selectionKey.channel();
            // 剔除发消息的客户端
            if (targetChannel instanceof SocketChannel && targetChannel != sourceSocketChannel) {
    
    
                try {
    
    
                    // 将消息发送到targetChannel客户端
                    ((SocketChannel) targetChannel).write(Charset.forName("UTF-8").encode(request));
                } catch (IOException e) {
    
    
                    e.printStackTrace();
                }
            }
        });
    }

}

2.2 客户端

客户端 -> NIOClient.java:

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Scanner;

/**
 * @author Administrator
 * @date 2021/4/9
 * NIO客户端
 */
public class NIOClient {
    
    
    /**
     * 客户端启动方式：
     * 1、直接启动此处的main方法
     * 2、单独启动AClient、BClient、CClient中的main方法
     */
    public static void main(String[] args) throws IOException {
    
    
        new NIOClient().start("客户端");
    }

    public void start(String nickName) throws IOException {
    
    
        // 连接服务器端
        SocketChannel socketChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 8000));
        // 新开线程，专门负责来接收服务器端的响应数据
        Selector selector = Selector.open();
        socketChannel.configureBlocking(false);
        socketChannel.register(selector, SelectionKey.OP_READ);
        new Thread(new NIOClientHandler(selector)).start();

        // 向服务器端发送数据
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextLine()) {
    
    
            String request = scanner.nextLine();
            if (request != null && request.length() > 0) {
    
    
                socketChannel.write(Charset.forName("UTF-8").encode(nickName + " : " + request));
            }
        }
    }
}

客户端数据响应线程类 -> NIOClientHandler.java:

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.Set;

/**
 * @author Administrator
 * @date 2021/4/9
 */
public class NIOClientHandler implements Runnable {
    
    
    private Selector selector;

    public NIOClientHandler(Selector selector) {
    
    
        this.selector = selector;
    }

    @Override
    public void run() {
    
    
        try {
    
    
            for (; ; ) {
    
    
                int readyChannels = selector.select();
                if (readyChannels == 0) {
    
    
                    continue;
                }

                // 获取可用的channel集合
                Set<SelectionKey> selectionKeys = selector.selectedKeys();
                Iterator iterator = selectionKeys.iterator();
                while (iterator.hasNext()) {
    
    
                    // selectionKey实例
                    SelectionKey selectionKey = (SelectionKey) iterator.next();
                    // 移除Set中的当前selectionKey
                    iterator.remove();
                    // 根据就绪状态，调用对应的业务处理方法
                    if (selectionKey.isReadable()) {
    
    
                        readHandler(selectionKey, selector);
                    }
                }
            }
        } catch (IOException e) {
    
    
            e.printStackTrace();
        }
    }

    /**
     * 可读事件处理器
     */
    private void readHandler(SelectionKey selectionKey, Selector selector) throws IOException {
    
    
        // 要从selectionKey中获取到已经就绪的channel
        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
        // 创建buffer
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        // 循环读取服务器端响应数据
        String response = "";
        while (socketChannel.read(byteBuffer) > 0) {
    
    
            // 切换buffer为读模式
            byteBuffer.flip();
            // 读取buffer中的内容
            response += Charset.forName("UTF-8").decode(byteBuffer);
        }

        // 将channel再次注册到selector上，监听可读事件
        socketChannel.register(selector, SelectionKey.OP_READ);
        // 将服务器端响应信息打印到本地
        if (response.length() > 0) {
    
    
            System.out.println(response);
        }
    }
}

单独写的3个客户端类
AClient.java:

import java.io.IOException;

/**
 * @author Administrator
 * @date 2021/4/9
 */
class AClient {
    
    
    public static void main(String[] args) throws IOException {
    
    
        new NIOClient().start("AClient");
    }
}

BClient.java:

import java.io.IOException;

/**
 * @author Administrator
 * @date 2021/4/9
 */
class BAClient {
    
    
    public static void main(String[] args) throws IOException {
    
    
        new NIOClient().start("BClient");
    }
}

CClient.java:

import java.io.IOException;

/**
 * @author Administrator
 * @date 2021/4/9
 */
class CClient {
    
    
    public static void main(String[] args) throws IOException {
    
    
        new NIOClient().start("CClient");
    }
}

2.3 测试结果

测试结果：

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