管道（pipe）示例（带注释）

pipe 说明

管道可以被用来仅在同一个 Java 虚拟机内部传输数据。虽然有更加有效率的方式来在线程之间传输数据，但是使用管道的好处在于封装性。¹

code

package com.nio.demo;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.Pipe;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;
import java.util.Random;

public class PipeTest {

	public static void main(String[] args) throws Exception {
		// 创建一个可写通道，用于向控制台输出管道中的内容
		WritableByteChannel out = Channels.newChannel(System.out);
		//启动一个工作线程，向管道写入数据，返回值为管道读的一端
		ReadableByteChannel readableByteChannel = startWorker(10);
		//创建一个缓冲区，用于接收管道中的数据
		ByteBuffer buffer = ByteBuffer.allocate(100);
		//如果工作线程中的管道一端不关闭，这个地方会一直阻塞在这里，即使没有数据传输
		while(readableByteChannel.read(buffer)>=0) {
			//将缓冲区翻转成一个准备读出元素的释放状态
			buffer.flip();
			//输出到控制台
			out.write(buffer);
			//清空缓冲区
			buffer.clear();
		}

	}

	private static ReadableByteChannel startWorker(int reps) throws Exception {
		//打开一个管道
		Pipe pipe = Pipe.open();
		//创建工作线程，并打开管道写的一端(pipe.sink())
		Worker worker=new Worker(pipe.sink(), reps);
		worker.start();
		//返回管道读的一端
		return (pipe.source());
	}
	//工作线程类
	private static class Worker extends Thread {
		WritableByteChannel channel;
		private int reps;

		public Worker(WritableByteChannel channel, int reps) {
			this.channel = channel;
			this.reps = reps;
		}

		@Override
		public void run() {
			ByteBuffer buffer = ByteBuffer.allocate(100);
			try {
				for (int i = 0; i < reps; i++) {
					doSomeWork(buffer);
					while (channel.write(buffer) > 0) {
						// empty
					}
				}
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}

		private String[] products = { "No good deed goes unpunished", "To be, or what?",
				"No matter where you go, there you are", "Just say \"Yo\"", "My karma ran over my dogma" };
		private Random rand = new Random();

		private void doSomeWork(ByteBuffer buffer) {
			int product = rand.nextInt(products.length);
			buffer.clear();
			buffer.put(products[product].getBytes());
			buffer.put("\r\n".getBytes());
			buffer.flip();
		}

	}

}

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1. 《Java Nio》 ↩︎