piped线程通信

    一个线程发送数据到输出管道，另一个线程从输入管道中读取数据。通过使用管道，实现不同线程间的通信，而无须借助于类似临时文件之类的东西。
    在java的jdk中提供了4个类来使线程间可以进行通信：
        PipedInputStream 和 PipedOutputStream
        PipedReader 和 PipedWriter

public static class ReadClient implements Runnable{
	private PipedInputStream reader;
	public ReadClient(PipedInputStream reader) {
		this.reader = reader;
	}
	@Override
	public void run() {
		byte[] bytes = new byte[50];
		try {
			do {
				int readLength = reader.read(bytes);//方法会一直阻塞，直到有数据被写入
				if(readLength==-1){continue;}
				String message = new String(bytes,0,readLength);
				System.out.println("get: "+message);
			}while(true);
		} catch (IOException e) {
			//something 
		}finally{
			try {
				reader.close();
			} catch (IOException e) {
				//something 
			}
		}
	}
}

public static class WriteClient implements Runnable{
	private PipedOutputStream writer;
	public WriteClient(PipedOutputStream writer) {
		this.writer = writer;
	}
	@Override
	public void run() {
		int seed = 0;
		try {
			while (true) {
				seed++;
				String message = ""+seed;
				System.out.println("send: "+seed);
				writer.write(message.getBytes());
				writer.flush();
				Thread.sleep(1000);
			}
		} catch (InterruptedException | IOException e) {
			//something 
		}finally{
			try {
				writer.close();
			} catch (IOException e) {
				//something 
			}
		}
		
	}
	
}

public static void main(String[] args) throws InterruptedException, IOException {
	PipedInputStream inputStream = new PipedInputStream();
	PipedOutputStream outputStream = new PipedOutputStream();
	//管道连接
	inputStream.connect(outputStream); //或 outputStream.connect(inputStream);
	//创建读写线程
	Thread reader = new Thread(new ReadClient(inputStream));
	reader.start();
	Thread.sleep(2000);
	Thread writer = new Thread(new WriteClient(outputStream));
	writer.start();
	
}

结果：
send: 1
get: 1
send: 2
get: 2
send: 3
get: 3

在main方法中，读的线程先启动了，所以在read时会阻塞直到writer线程开始写数据。如果writer先启动，数据也不会丢失，会一直写入到管道中。直到reader线程去读取它。