非阻塞通信(服务器端)

一.非阻塞
1.非阻塞:线程执行方法时,如果操作没有就绪,就立即返回,不会一直等待操作就绪

2.java.nio提供非阻塞通信的类:
1)ServerSocketChannel:代替Server
2)SocketChannel:代替Socket
3)Selector:监控就绪事件
4)SelectionKey:注册事件的句柄

3.服务器端程序使用多线程处理阻塞IO,虽然可以响应多用户,但是存在局限性
1)JVM会给每个线程分配独立的资源,线程越多,系统开销越大
2)容易造成死锁
3)需要频繁转让CPU使用

4.完成多个任务可以使用多线程分别处理,也可以让单个线程以轮询的工作方式处理就绪的任务

二.创建非阻塞服务器端程序
对于服务区端造成阻塞的原因有:
1)客户端的连接
2)接收客户端的数据
3)响应客户端的数据
所以,可以在主线程中分别监控这些任务,当有任何一个就绪就执行

public class nio_demo2 {

    private Selector selector = null;
    private ServerSocketChannel serverSocketChannel = null;
    private int port = 6666;
    private Charset charset = Charset.forName("UTF-8");

    public nio_demo2() throws IOException {

        selector = Selector.open();
        serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.socket().setReuseAddress(true);
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.socket().bind(new InetSocketAddress(port));
        System.out.println("server start...");
    }

    public void service() throws IOException {

        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        //select():监控注册的channel,当有需要处理的IO时,将对应的selectionKey加入到selected-key集合
        while(selector.select()>0){

            Set readyKey = selector.selectedKeys();
            Iterator it = readyKey.iterator();
            while(it.hasNext()){
                SelectionKey key = null;
                try{
                    key = (SelectionKey)it.next();
                    it.remove();

                    if(key.isAcceptable()){
                        ServerSocketChannel ssc = (ServerSocketChannel)key.channel();
                        SocketChannel socketChannel = ssc.accept();
                        System.out.println("client connection" +
                                socketChannel.socket().getInetAddress()+":"
                                +socketChannel.socket().getPort());
                        //设置为非阻塞
                        socketChannel.configureBlocking(false);
                        ByteBuffer buffer = ByteBuffer.allocate(1024);
                        //向selecctor注册读就绪事件和写就绪时件,同时关联buffer
                        socketChannel.register(selector,
                                SelectionKey.OP_READ|SelectionKey.OP_WRITE,buffer);
                    }

                    if(key.isReadable()){
                        receive(key);
                    }
                    if(key.isWritable()){
                        send(key);
                    }
                }catch (IOException e){
                    e.printStackTrace();
                    try{
                        if(key!=null){
                            key.cancel();
                            key.channel().close();
                        }
                    }catch(Exception ex){
                        ex.printStackTrace();
                    }

                }

            }
        }
    }
    //发送,处理写就绪事件
    public void send(SelectionKey key) throws IOException {
        //获得关联的附件
        ByteBuffer buffer = (ByteBuffer)key.attachment();
        SocketChannel socketChannel = (SocketChannel)key.channel();
        buffer.flip();
        String data = decode(buffer);
        if(data.indexOf("\n")==-1){
            return;
        }
        String outputData = data.substring(0,data.indexOf("\n")+1);
        System.out.println(outputData);
        ByteBuffer outputBuffer = encode("echo:"+outputData);
        //发送一行数据
        while(outputBuffer.hasRemaining()){
            socketChannel.write(outputBuffer);
        }
        //删除已处理数据(读写操作同一个ByteBuffer)
        ByteBuffer temp = encode(outputData);
        buffer.position(temp.limit());
        buffer.compact();

        if(outputData.equals("end\n")){
            key.cancel();
            socketChannel.close();
            System.out.println("close coonnection");
        }
    }
    //接收,处理读就绪事件
    public void receive(SelectionKey key) throws IOException {
        //获取关联的buffer
        ByteBuffer buffer = (ByteBuffer)key.attachment();
        //获取关联的channel
        SocketChannel socketChannel = (SocketChannel)key.channel();
        ByteBuffer readBuffer = ByteBuffer.allocate(32);
        socketChannel.read(readBuffer);
        //flip:将极限设置为位置,将位置设置为0
        readBuffer.flip();

        buffer.limit(buffer.capacity());
        buffer.put(readBuffer);
    }
    //解码
    public String decode(ByteBuffer buffer){
        CharBuffer charBuffer = charset.decode(buffer);
        return charBuffer.toString();
    }
    //编码
    public ByteBuffer encode(String str){
        return charset.encode(str);
    }

    public static void main(String[] args) throws IOException {
        nio_demo2 server = new nio_demo2();
        server.service();
    }
}