How to handle concurrent connections in Java network programming?

There are two ways to handle concurrent connections in Java network programming: Thread pool: Create a pre-created and managed thread pool, and obtain threads from the thread pool to handle the connection when the client connects. NIO Selector: Process multiple connections in one thread. When the client connects or data is readable, the event is triggered and then processed.

Concurrent connection handling in Java network programming

In Java network programming, handling concurrent connections is crucial. Concurrent connections are when an application handles multiple clients accessing it at the same time.

Thread Pool

A common method of concurrent processing is to use a thread pool. A thread pool is a pre-created and managed group of threads. When a client connects, a thread can be obtained from the thread pool to handle the connection. This prevents new threads from being created for each connection, thus saving resources.

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class ThreadPoolServer {

    public static void main(String[] args) {
        // 创建一个线程池，指定线程数
        ExecutorService threadPool = Executors.newFixedThreadPool(10);

        // 创建ServerSocket监听端口
        ServerSocket serverSocket = new ServerSocket(8080);

        while (true) {
            // 等待客户端连接
            Socket clientSocket = serverSocket.accept();

            // 从线程池中获取一个线程处理客户端连接
            threadPool.execute(new ClientHandler(clientSocket));
        }
    }

    private static class ClientHandler implements Runnable {

        private Socket clientSocket;

        public ClientHandler(Socket clientSocket) {
            this.clientSocket = clientSocket;
        }

        @Override
        public void run() {
            // 处理客户端连接
            try {
                // 获取客户端输入
                BufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                String line = reader.readLine();
                
                // 向客户端发送响应
                BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
                writer.write("HTTP/1.1 200 OK\n");
                writer.flush();
                
                // 关闭连接
                clientSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

NioSelector

Another option for handling concurrent connections is to use a NIO Selector. NIO Selector allows multiple connections to be handled in a single thread. The Selector triggers events when the client connects or data is readable.

import java.io.IOException;
import java.net.InetSocketAddress;
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;

class NioServer {

    public static void main(String[] args) throws IOException {
        // 创建ServerSocketChannel监听端口
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(8080));

        // 设置ServerSocketChannel为非阻塞模式
        serverSocketChannel.configureBlocking(false);

        // 创建Selector
        Selector selector = Selector.open();

        // 将ServerSocketChannel注册到Selector的ACCEPT事件
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        while (true) {
            // 阻塞等待事件发生
            selector.select();

            // 获取发生的事件
            Set<SelectionKey> keys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = keys.iterator();

            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                iterator.remove();

                // 处理ACCEPT事件
                if (key.isAcceptable()) {
                    SocketChannel socketChannel = serverSocketChannel.accept();

                    // 设置SocketChannel为非阻塞模式
                    socketChannel.configureBlocking(false);

                    // 将SocketChannel注册到Selector的READ事件
                    socketChannel.register(selector, SelectionKey.OP_READ);
                } 

                // 处理READ事件
                else if (key.isReadable()) {
                    // 处理客户端连接
                    handleClientConnection(key);
                }
            }
        }
    }

    private static void handleClientConnection(SelectionKey key) throws IOException {
        SocketChannel socketChannel = (SocketChannel) key.channel();

        // 获取客户端输入
        BufferedReader reader = new BufferedReader(new InputStreamReader(socketChannel.socket().getInputStream()));
        String line = reader.readLine();

        // 向客户端发送响应
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socketChannel.socket().getOutputStream()));
        writer.write("HTTP/1.1 200 OK\n");
        writer.flush();

        // 取消注册Selector的事件
        key.cancel();

        // 关闭连接
        socketChannel.close();
    }
}

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