Java多线程问题--PipedInputStream和PipedOutputStream实现线程间通信

本文内容部分引自《Java多线程编程核心技术》，感谢作者！！！

代码地址：https://github.com/xianzhixianzhixian/thread.git

相关知识讲解

1、Java中提供了很多输入/输出流Stream，其中管道流(pipeStream)是一种特殊的流，用于在不同线程间直接传送数据。一个线程发送数据到输入管道，另一个线程从输入管道中读取数据。通过使用管道，可以实现不同线程间的通信，无需借助于类似临时文件之类的东西。

2、使用PipedInputStream和PipedOutputStream可以实现线程间通信：PipedInputStream用于从管道中读取字节流数据，PipedOutputStream用于向管道中写入字节流数据。

3、使用PipedInputStream中的connect(PipedOutputStream实例)或PipedOutputStream中的connect(PipedInputStream实例)来连接管道从而进行读写字节流数据，两者不可同时使用，否则会报java.io.IOException: Already connected错误。

代码示例

ReadData.java

/**
 * 使用PipedInputStream和PipedOutputStream实现线程间通信
 * @author: xianzhixianzhixian
 * @date: 2019-01-02 19:39
 */
public class ReadData {

    public void readMethod(PipedInputStream input){
        try {
            System.out.println("read：");
            byte[] byteArray = new byte[20];
            int readLength = input.read(byteArray);
            while (readLength != -1){
                String newData = new String(byteArray, 0, readLength);
                System.out.print(newData);
                readLength = input.read(byteArray);
            }
            System.out.println();
            input.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

WriteData.java

/**
 * 使用PipedInputStream和PipedOutputStream实现线程间通信
 * @author: xianzhixianzhixian
 * @date: 2019-01-02 19:36
 */
public class WriteData {

    public void writeMethod(PipedOutputStream out){
        try {
            System.out.println("write：");
            for (int i = 0; i < 300; i++) {
                String outData = "" + (i + 1);
                out.write(outData.getBytes());
                System.out.print(outData);
            }
            System.out.println();
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

ThreadRead.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-02 19:45
 */
public class ThreadRead extends Thread {

    private ReadData read;
    private PipedInputStream input;

    public ThreadRead(ReadData read, PipedInputStream input) {
        this.read = read;
        this.input = input;
    }

    @Override
    public void run() {
        super.run();
        read.readMethod(input);
    }
}

ThreadWrite.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-02 19:43
 */
public class ThreadWrite extends Thread {

    private WriteData write;
    private PipedOutputStream out;

    public ThreadWrite(WriteData write, PipedOutputStream out) {
        this.write = write;
        this.out = out;
    }

    @Override
    public void run() {
        super.run();
        write.writeMethod(out);
    }
}

Run.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-02 19:46
 */
public class Run {

    public static void main(String[] args) {
        try {
            WriteData writeData = new WriteData();
            ReadData readData = new ReadData();

            PipedInputStream inputStream = new PipedInputStream();
            PipedOutputStream outputStream = new PipedOutputStream();

            inputStream.connect(outputStream);
            //outputStream.connect(inputStream);

            /**
             * 在代码中首先启动的是threadRead，由于当时没有数据被写入，所以线程阻塞在
             * int readLength=input.read(byteArray);直到有数据写入后，才继续向下运行。
             */
            ThreadRead threadRead = new ThreadRead(readData, inputStream);
            threadRead.start();

            Thread.sleep(2000);

            ThreadWrite threadWrite = new ThreadWrite(writeData, outputStream);
            threadWrite.start();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

运行结果：注意Run.java中先调用的是threadRead.start()，但是打印结果的时候还是先write后read的，因为虽然在代码中首先启动的是threadRead，由于当时没有数据被写入，所以线程阻塞在int readLength=input.read(byteArray);直到有数据写入后，才继续向下运行