2.java nio 网络编程 client端

   前面写了nio 网络 server端，这里是client端，只写了简单的发送接收数据，最后关闭连接。大文本发送和接手参考server端写法就行了。

   

    不过这里有个异常，客户端这边调用socketChannel的close方法以后，服务端继续使用这个channel的话，会抛出异常。所以在server端需要检查，socketChannel.read(rb)这个方法会返回一个整数，当返回的数大于-1的时候，表示这个socketChannel没有close，当socketChannel调用close方法以后，会返回-1，这时候，就不要操作这个socketChannel还有不要调用SelectionKey的interestOps方法，这里面也会用到这个socketChannel。

   

package com.govert.project;

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.SocketChannel;
import java.util.Set;

/**
 * Created by govert on 2016/8/21.
 */
public class NioClient {

    public static void main(String[] args) throws IOException {
        // read and write byte buffer
        ByteBuffer rb = ByteBuffer.allocate(1024);
        ByteBuffer wb = ByteBuffer.allocate(1024);

        // connect hostname and port
        String hostname = "127.0.0.1";
        int port = 9000;

        // open Selector & check
        Selector selector = Selector.open();
        if (selector.isOpen()) {
            System.err.println("Selector open success.");
        }

        // open SocketChannel & check
        SocketChannel socketChannel = SocketChannel.open();
        if (socketChannel.isOpen()) {
            System.err.println("SocketChannel open success.");
        }

        // config non-block & connect
        socketChannel.configureBlocking(false);
        socketChannel.connect(new InetSocketAddress(hostname, port));

        // socketChannel register selector
        socketChannel.register(selector, SelectionKey.OP_CONNECT);

        // hand event loop
        boolean isExit = false;
        while (!isExit) {

            selector.select();

            Set<SelectionKey> keys = selector.selectedKeys();
            for (SelectionKey key : keys) {
                if (key.isReadable()) {

                    rb.clear();
                    socketChannel.read(rb);
                    rb.flip();
                    System.err.println(new String(rb.array(), 0, rb.limit(), "utf-8"));


                    // key.interestOps(SelectionKey.OP_WRITE);
                    //
                    key.cancel();
                    socketChannel.close();
                    isExit = true;
                } else if (key.isWritable()) {

                    String req = "hello server, i am from client.";
                    wb.clear();
                    wb.put(req.getBytes("utf-8"));
                    wb.flip();
                    socketChannel.write(wb);

                    key.interestOps(SelectionKey.OP_READ);
                } else if (key.isConnectable()) {
                    socketChannel.finishConnect();

                    System.err.println("client connect server success.");

                    key.interestOps(SelectionKey.OP_WRITE);
                }
            }

            //
            keys.clear();
        }

    }
}