Java 函数如何使用 NIO 技术处理高并发请求？

java nio 是一种处理高并发请求的高效技术，使用非阻塞 i/o 和轮询机制实现：创建 nio selector 监听事件；注册 channel 到 selector，监听 accept 事件；循环等待事件，处理 accept、read、write 事件；accept 事件处理客户端连接，创建 socketchannel；read 事件读取数据，write 事件回写数据。

Java 函数使用 NIO 处理高并发请求

简介
非阻塞 I/O (NIO) 是 Java 中一种用于处理大量并发请求的高效技术。它通过异步操作和轮询机制，有效地利用系统资源，提升系统吞吐量。

步骤
1. 创建 NIO Selector
NIO Selector 用于监听注册的 Channel 上的事件。

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Selector selector = Selector.open();

2. 注册 Channel
将 ServerSocketChannel 注册到 Selector，监听 ACCEPT 事件。

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ServerSocketChannel serverChannel = ServerSocketChannel.open();
serverChannel.configureBlocking(false);
serverChannel.register(selector, SelectionKey.OP_ACCEPT);

3. 循环等待事件
通过 Selector.select() 方法监听事件。

while (true) {
    selector.select();
    Set keys = selector.selectedKeys();
    // 处理事件...
}

4. 处理 ACCEPT 事件
当 ACCEPT 事件发生时，接受连接并创建 SocketChannel。

if (key.isAcceptable()) {
    ServerSocketChannel channel = (ServerSocketChannel) key.channel();
    SocketChannel clientChannel = channel.accept();
    clientChannel.configureBlocking(false);
    clientChannel.register(selector, SelectionKey.OP_READ);
}

实战案例
以下是一个简单的 Java NIO Echo 服务器示例。它监听客户端连接，并回显收到的消息。

EchoServer.java

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;

public class EchoServer {

    private Selector selector;
    private ServerSocketChannel serverChannel;
    private int port;

    public EchoServer(int port) {
        this.port = port;
    }

    public void start() throws IOException {
        // 创建 Selector
        selector = Selector.open();

        // 创建 ServerSocketChannel
        serverChannel = ServerSocketChannel.open();
        serverChannel.configureBlocking(false);
        serverChannel.bind(new InetSocketAddress(port));
        serverChannel.register(selector, SelectionKey.OP_ACCEPT);

        // 不断循环等待事件
        while (true) {
            int keysCount = selector.select();
            if (keysCount == 0) {
                continue;
            }
            Set keys = selector.selectedKeys();
            for (SelectionKey key : keys) {
                try {
                    if (key.isAcceptable()) {
                        handleAccept(key);
                    } else if (key.isReadable()) {
                        handleRead(key);
                    } else if (key.isWritable()) {
                        handleWrite(key);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                    key.cancel();
                    SocketChannel channel = (SocketChannel) key.channel();
                    channel.close();
                }
            }
            keys.clear();
        }
    }

    private void handleAccept(SelectionKey key) throws IOException {
        ServerSocketChannel channel = (ServerSocketChannel) key.channel();
        SocketChannel clientChannel = channel.accept();
        clientChannel.configureBlocking(false);
        clientChannel.register(selector, SelectionKey.OP_READ);
    }

    private void handleRead(SelectionKey key) throws IOException {
        SocketChannel channel = (SocketChannel) key.channel();
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        int readBytes = channel.read(buffer);
        if (readBytes == -1) {
            channel.close();
            return;
        }
        buffer.flip();
        channel.write(buffer);
    }

    private void handleWrite(SelectionKey key) throws IOException {
        SocketChannel channel = (SocketChannel) key.channel();
        channel.write(ByteBuffer.allocate(1024));
    }

    public static void main(String[] args) throws IOException {
        new EchoServer(9090).start();
    }
}