一、使用NIO完成网络通信的三个核心
1、通道（Channel）:负责连接
java.nio.channels.Channel 接口
|– SelectableChannel
|– SocketChannel
|–ServerChannel
|–DatagramChannel
|–Pipe.SinkChannel
|–Pipe.SourceChannel

2、缓冲区（Buffer）: 负责数据的存取
3、选择器（Selector）: 是SelectableChannel 的多路复用器，用于监控SelectableChannel 的IO状况

阻塞

package nio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

import org.junit.Test;

public class TestBlockingNIO {
    @Test
    public void client() throws IOException{
        //1、获取通道
        SocketChannel sChannel=SocketChannel.open(new InetSocketAddress("127.0.0.1",9898));
        FileChannel inChannel=FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
        //2、获取指定大小的缓冲区域
        ByteBuffer buf=ByteBuffer.allocate(1024);
        //3、读取本地文件，并发送到服务端去
        while(inChannel.read(buf)!=-1){
            buf.flip();
            sChannel.write(buf);
            buf.clear();
        }
        //4、关闭通道
        inChannel.close();
        sChannel.close();
    }

    @Test
    public void server() throws IOException{
        //1、获取通道
        ServerSocketChannel ssChannel=ServerSocketChannel.open();
        FileChannel outChannel=FileChannel.open(Paths.get("2.jpg"),StandardOpenOption.WRITE,StandardOpenOption.CREATE);
        //2、绑定连接
        ssChannel.bind(new InetSocketAddress(9898));
        //3、获取客户端连接的通道
        SocketChannel sChannel=ssChannel.accept();
        //4、分配指定大小的缓冲区
        ByteBuffer buf=ByteBuffer.allocate(1024);
        //5、接受客户端的数据，并保存到本地
        while(sChannel.read(buf)!=-1){
            buf.flip();
            outChannel.write(buf);
            buf.clear();
        }
        //6、关闭通道
        sChannel.close();
        ssChannel.close();
        outChannel.close();
    }
}

非阻塞

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.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Date;
import java.util.Iterator;
import java.util.Scanner;

import org.junit.Test;

/* * 一、使用 NIO 完成网络通信的三个核心： * * 1. 通道（Channel）：负责连接 * * java.nio.channels.Channel 接口： * |--SelectableChannel * |--SocketChannel * |--ServerSocketChannel * |--DatagramChannel * * |--Pipe.SinkChannel * |--Pipe.SourceChannel * * 2. 缓冲区（Buffer）：负责数据的存取 * * 3. 选择器（Selector）：是 SelectableChannel 的多路复用器。用于监控 SelectableChannel 的 IO 状况 * */
public class TestNonBlockingNIO {

    //客户端
    @Test
    public void client() throws IOException{
        //1. 获取通道
        SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 9898));

        //2. 切换非阻塞模式
        sChannel.configureBlocking(false);

        //3. 分配指定大小的缓冲区
        ByteBuffer buf = ByteBuffer.allocate(1024);

        //4. 发送数据给服务端
        Scanner scan = new Scanner(System.in);

        while(scan.hasNext()){
            String str = scan.next();
            buf.put((new Date().toString() + "\n" + str).getBytes());
            buf.flip();
            sChannel.write(buf);
            buf.clear();
        }

        //5. 关闭通道
        sChannel.close();
    }

    //服务端
    @Test
    public void server() throws IOException{
        //1. 获取通道
        ServerSocketChannel ssChannel = ServerSocketChannel.open();

        //2. 切换非阻塞模式
        ssChannel.configureBlocking(false);

        //3. 绑定连接
        ssChannel.bind(new InetSocketAddress(9898));

        //4. 获取选择器
        Selector selector = Selector.open();

        //5. 将通道注册到选择器上, 并且指定“监听接收事件”
        ssChannel.register(selector, SelectionKey.OP_ACCEPT);

        //6. 轮询式的获取选择器上已经“准备就绪”的事件
        while(selector.select() > 0){

            //7. 获取当前选择器中所有注册的“选择键(已就绪的监听事件)”
            Iterator<SelectionKey> it = selector.selectedKeys().iterator();

            while(it.hasNext()){
                //8. 获取准备“就绪”的是事件
                SelectionKey sk = it.next();

                //9. 判断具体是什么事件准备就绪
                if(sk.isAcceptable()){
                    //10. 若“接收就绪”，获取客户端连接
                    SocketChannel sChannel = ssChannel.accept();

                    //11. 切换非阻塞模式
                    sChannel.configureBlocking(false);

                    //12. 将该通道注册到选择器上
                    sChannel.register(selector, SelectionKey.OP_READ);
                }else if(sk.isReadable()){
                    //13. 获取当前选择器上“读就绪”状态的通道
                    SocketChannel sChannel = (SocketChannel) sk.channel();

                    //14. 读取数据
                    ByteBuffer buf = ByteBuffer.allocate(1024);

                    int len = 0;
                    while((len = sChannel.read(buf)) > 0 ){
                        buf.flip();
                        System.out.println(new String(buf.array(), 0, len));
                        buf.clear();
                    }
                }

                //15. 取消选择键 SelectionKey
                it.remove();
            }
        }
    }
}