NIO的非阻塞通信

使用NIO完成网络通信的三个要点：

	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。

	说明：
		1)非阻塞模式是针对网络IO而言的。
		2)FileChannel不能切换成非阻塞模式。

		
举例：

	阻塞式的网络IO：

		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", 9999));
				//2. 分配指定大小的缓冲区
				ByteBuffer buf = ByteBuffer.allocate(1024);
				//3. 读取本地文件，并发送到服务端
				FileChannel inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
				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();
				//2. 绑定连接
				ssChannel.bind(new InetSocketAddress(9999));
				//3. 获取客户端连接的通道
				SocketChannel sChannel = ssChannel.accept(); // 阻塞式的等待远程连接
				//4. 分配指定大小的缓冲区
				ByteBuffer buf = ByteBuffer.allocate(1024);
				//5. 接收客户端的数据，并保存到本地
				FileChannel outChannel = FileChannel.open(Paths.get("2.jpg"), StandardOpenOption.WRITE, StandardOpenOption.CREATE);
				while(sChannel.read(buf) != -1){
					buf.flip();
					outChannel.write(buf);
					buf.clear();
				}
				//6. 关闭通道
				sChannel.close();
				outChannel.close();
				ssChannel.close();
			}
		}

	
	非阻塞式的网络IO：
	
		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;

		public class TestNonBlockingNIO {
			
			@Test
			public void client() throws IOException{
				//1. 获取通道
				SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 9999));
				//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
				scan.close();
				sChannel.close();
			}

			@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(9999));
				
				//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()){
							//10. 获取当前选择器上“读就绪”状态的通道
							SocketChannel sChannel = (SocketChannel) sk.channel();
							
							//11. 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();
					}
				}
			}
		}