ServerSocket和ServerSocketChannel实例

1.传统Socket

传统Socket单线程只能处理一个连接，要处理多个连接需要借助线程或者线程池，但是这样比较消耗资源。

public class ServerSocketDemo {

    public static void main(String[] args) throws IOException {
        new ServerSocketDemo().start(8080);
    }
    private  void start(int port) throws IOException {
        ServerSocket serverSocket = new ServerSocket(port,2000);
        System.out.println("server is start!");
        //线程池可以处理多个连接比较消耗性能
        ExecutorService executorService= Executors.newCachedThreadPool();
        try {
            while (true) {
                //accept 会阻塞
                Socket socket = serverSocket.accept();
                System.out.println("有客户端连接来了"+socket.toString());
                executorService.execute(new SocketHandler(socket));
            }
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        } finally {
            serverSocket.close();
        }
    }
}

public class SocketHandler implements Runnable {
    private Socket socket;

    public SocketHandler(Socket socket) {
        this.socket = socket;
    }

    public void run() {
        InputStream in = null;
        OutputStream out = null;
        try {
            in = socket.getInputStream();
            out = socket.getOutputStream();
            byte[] bytes = new byte[1024];
            while (true) {
                //会阻塞
                int n = in.read(bytes);
                if (n == -1) {
                    break;
                }
                System.out.println(new String(bytes, 0, n));
                out.write(bytes,0,n);
            }
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        } finally {
            try {
                System.out.print("关闭 socket");
                socket.close();
            } catch (Exception ex) {
                System.out.println(ex.getMessage());
            }
            try {
                if(in!=null) {
                    in.close();
                }
            } catch (Exception ex) {
                System.out.println(ex.getMessage());
            }
            try {
                if(out!=null) {
                    out.close();
                }
            } catch (Exception ex) {
                System.out.println(ex.getMessage());
            }
        }
    }

}

2.NIO

java nio 借鉴了Linux下select、poll、epoll模型；其性能有很大的提高。

public class ServerSocketChannelDemo {
    private Selector selector;

    public void initServer(int port) throws IOException {
        //创建ServerSocketChannel
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.socket().bind(new InetSocketAddress(port));
        this.selector = Selector.open();
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
    }

    public void listen() throws IOException {
        System.out.println("server is start!");
        while (true) {
            //这条语句会阻塞
            selector.select();
            Iterator<SelectionKey> iterator = this.selector.selectedKeys().iterator();
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                iterator.remove();
                handler(key);
            }

        }
    }

    public void handler(SelectionKey key) throws IOException {
        if (key.isAcceptable()) {
            handlerAccept(key);
        } else if (key.isReadable()) {
            handlerReader(key);
        }
    }

    public void handlerAccept(SelectionKey key) throws IOException {
        ServerSocketChannel sever = (ServerSocketChannel) key.channel();
        SocketChannel channel = sever.accept();
        channel.configureBlocking(false);
        System.out.println("有客服端连接来了" + channel.toString());
        channel.register(this.selector, SelectionKey.OP_READ);
    }

    public void handlerReader(SelectionKey key) throws IOException {
        SocketChannel socketChannel = (SocketChannel) key.channel();
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        //不会阻塞
        int n = socketChannel.read(buffer);
        System.out.println(n);
        if (n > 0) {
            byte[] data = buffer.array();
            System.out.println("服务端收到信息:" + new String(data, 0, n));
            buffer.flip();
            socketChannel.write(buffer);
        } else {
            System.out.println("clinet is close");
            key.cancel();
        }

    }

    public static void main(String[] args) throws IOException {
        ServerSocketChannelDemo sever = new ServerSocketChannelDemo();
        sever.initServer(8081);
        sever.listen();
    }

}

NIO 的基本知识可以参考：
IO 模型
缓冲区
通道
值得说明是：
selector.select()是阻塞的，selector.select(1000)是非阻塞的（1000 表示等待时间）、selector.selectNow()也是非阻塞的、selector.wakeup()可以唤醒selector。
SelectionKey.OP_WRITE一般很少使用OP_WRITE表示底层缓冲区是否有空间，是则响应返还true。