NIO系列-03-NIO

声明

该系列文章由书籍《Netty权威指南》第二版整理而来。只为记录学习笔记。
若认为内容侵权请及时通知本人删除相关内容。

时间服务器–NIO

服务端代码

服务端主程序

public class TimeServer {    public static void main(String[] args) {        int port = 1234;        try {            TimeServerDispatcher timeServer;            timeServer = new TimeServerDispatcher(port);            new Thread(timeServer).start();        } catch (IOException e) {            e.printStackTrace();        }    }}

服务端处理类

public class TimeServerDispatcher implements Runnable {    private Selector selector;    private ServerSocketChannel ssc;    private volatile boolean stop;    private DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");    public TimeServerDispatcher(int port) throws IOException {        selector = Selector.open();        ssc = ServerSocketChannel.open();        ssc.configureBlocking(false);        ssc.socket().bind(new InetSocketAddress(port), 10000);        ssc.register(selector, SelectionKey.OP_ACCEPT);        System.out.println("The time server is listening on port : " + port);    }    public void stop() {        this.stop = true;    }    @Override    public void run() {        while (!this.stop) {            try {                selector.select(1000);                Set<SelectionKey> selectedKeys = selector.selectedKeys();                for (SelectionKey k : selectedKeys) {                    selectedKeys.remove(k);                    try {                        doProcessRequest(k);                    } catch (Exception e) {                        if (k != null) {                            k.cancel();                            if (k.channel() != null)                                k.channel().close();                        }                    }                }            } catch (Throwable t) {                t.printStackTrace();            }        }        if (selector != null) {            try {                selector.close();            } catch (IOException e) {                e.printStackTrace();            }        }    }    private void doProcessRequest(SelectionKey key) throws IOException {        if (!key.isValid())            return;        if (key.isAcceptable()) {            ServerSocketChannel ssc = (ServerSocketChannel) key.channel();            SocketChannel sc = ssc.accept();            sc.configureBlocking(false);            sc.register(selector, SelectionKey.OP_READ);        }        if (key.isReadable()) {            SocketChannel sc = (SocketChannel) key.channel();            ByteBuffer readBuffer = ByteBuffer.allocate(1024);            int len = sc.read(readBuffer);            if (len > 0) {                readBuffer.flip();                byte[] bytes = new byte[readBuffer.remaining()];                readBuffer.get(bytes);                String reqMsg = new String(bytes, "UTF-8");                System.out.println("request msg is : " + reqMsg);                String respMsg = this.df.format(new Date());                doResponse(sc, respMsg);            } else if (len < 0) {                key.cancel();                sc.close();            } else {                // 0            }        }    }    private void doResponse(SocketChannel sc, String respMsg) throws IOException {        if (respMsg == null)            return;        byte[] bytes = respMsg.getBytes();        ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);        writeBuffer.put(bytes);        writeBuffer.flip();        sc.write(writeBuffer);    }}

客户端代码

客户端主程序

public class TimeClient {    public static void main(String[] args) {        int port = 1234;        new Thread(new TimeClientHandler("127.0.0.1", port)).start();    }}

客户端处理程序

public class TimeClientHandler implements Runnable {    private String host;    private int port;    private Selector selector;    private SocketChannel socketChannel;    private volatile boolean stop;    public TimeClientHandler(String host, int port) {        this.host = host;        this.port = port;        try {            selector = Selector.open();            socketChannel = SocketChannel.open();            socketChannel.configureBlocking(false);        } catch (IOException e) {            e.printStackTrace();        }    }    @Override    public void run() {        try {            if (socketChannel.connect(new InetSocketAddress(host, port))) {                socketChannel.register(selector, SelectionKey.OP_READ);                doSendReqMsg(socketChannel, "Hi Server !");            } else                socketChannel.register(selector, SelectionKey.OP_CONNECT);        } catch (IOException e) {            e.printStackTrace();        }        while (!this.stop) {            try {                selector.select(1000);                Set<SelectionKey> selectedKeys = selector.selectedKeys();                for (SelectionKey k : selectedKeys) {                    selectedKeys.remove(k);                    try {                        doProcessResponse(k);                    } catch (Exception e) {                        if (k != null) {                            k.cancel();                            if (k.channel() != null)                                k.channel().close();                        }                    }                }            } catch (Exception e) {                e.printStackTrace();            }        }        if (selector != null) {            try {                selector.close();            } catch (IOException e) {                e.printStackTrace();            }        }    }    private void doProcessResponse(SelectionKey key) throws IOException {        if (!key.isValid())            return;        SocketChannel sc = (SocketChannel) key.channel();        if (key.isConnectable()) {            if (sc.finishConnect()) {                sc.register(selector, SelectionKey.OP_READ);                doSendReqMsg(sc, "Hi Server !");            } else {                throw new RuntimeException("连接失败");            }        }        if (key.isReadable()) {            ByteBuffer readBuffer = ByteBuffer.allocate(1024);            int readBytes = sc.read(readBuffer);            if (readBytes > 0) {                readBuffer.flip();                byte[] bytes = new byte[readBuffer.remaining()];                readBuffer.get(bytes);                String respMsg = new String(bytes, "UTF-8");                System.out.println("time : " + respMsg);                this.stop = true;            } else if (readBytes < 0) {                key.cancel();                sc.close();            } else {                // 0            }        }    }    private void doSendReqMsg(SocketChannel sc, String reqMsg) throws IOException {        byte[] req = reqMsg.getBytes();        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);        writeBuffer.put(req);        writeBuffer.flip();        sc.write(writeBuffer);    }}

总结

这种模型有如下特点:

• 客户端的连接操作时异步的
• SocketChannel的读写操作是异步的
• 一个Selector可以处理成千上万个客户端连接

但是：

• 代码复杂
• 这里的实现可能出现 “读半包”,”写半包”的情况

参考资料: 《Netty权威指南》第二版