java多线程编程之管道通信详解

上一章节讲了wait/notify通信，这一节我们来探讨使用管道进行通信。

java中提供了IO流使我们很方便的对数据进行操作，pipeStream是一种特殊的流，用于不同线程间直接传送数据。一个线程将数据发送到输出管道，另一个线程从输入管道读取数据。通过管道实现通信不需要借助临时文件这类东西。

java中提供了四个类使得线程间可以通信：

①字节流：PipeInputStream，PipedOutputStream
②字符流：PipedReader，PipedWriter

下面我们看看字节流的实现方法：

package pipeInputOutput;
//输出流
import java.io.IOException;
import java.io.PipedOutputStream;
public class WriteDate {
 public void writeMethod(PipedOutputStream out) {
  try {
   System.out.println("write:");
   for(int i=0;i<300;i++) {
    String outDate=""+(i+1);
    out.write(outDate.getBytes());
    System.out.print(outDate);
   }
   System.out.println();
   out.close();
  }catch(IOException e) {
   e.printStackTrace();
  }
 }
}

package pipeInputOutput;
//输入流
import java.io.IOException;
import java.io.PipedInputStream;

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

package pipeInputOutput;
import java.io.PipedOutputStream;
//输出线程
public class ThreadWrite extends Thread {
 private WriteDate write;
 private PipedOutputStream out;

 public ThreadWrite(WriteDate write,PipedOutputStream out) {
  super();
  this.write=write;
  this.out=out;
 }
 public void run() {
  write.writeMethod(out);
 }

}

package pipeInputOutput;
import java.io.PipedInputStream;
//输入线程
public class ThreadRead extends Thread{
 private ReadDate read;
 private PipedInputStream in;
 public ThreadRead(ReadDate read,PipedInputStream in) {
  super();
  this.read=read;
  this.in=in;
 }
 public void run() {
  read.ReadDate(in);
 }

}

package pipeInputOutput;
import java.io.IOException;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
//测试方法
public class Run {
 public static void main(String[] args) {
  try {
   WriteDate write=new WriteDate();
   ReadDate read=new ReadDate();
   PipedInputStream inputStream=new PipedInputStream();
   PipedOutputStream outputStream=new PipedOutputStream();
   //输出流与输入流进行连接。
   outputStream.connect(inputStream);
   //inputStream.connect(outputStream);
   ThreadRead readThread=new ThreadRead(read,inputStream);
   readThread.start();//先启动输出线程
   Thread.sleep(2000);
   ThreadWrite writeThread=new ThreadWrite(write,outputStream);
   writeThread.start();//后启动输入线程
  } catch (IOException e) {
   e.printStackTrace();
  } catch (InterruptedException e) {
   e.printStackTrace();
  }
 }

}

控制台输出：

read:
write:
123456789101112131415161718192021...
123456789101112131415161718192021...

上面测试中，先启动输入线程，然后因为没有线程被写入所以线程被阻塞，知道有数据写入。

我们接着继续看看字符流的实现方法：

package pipeInputOutput1;
import java.io.IOException;
import java.io.PipedWriter;
//字符输出流
public class WriteDate {
 public void writeMethod(PipedWriter out) {
  try {
   System.out.println("write:");
   for(int i=0;i<300;i++) {
    String outDate=""+(i+1);
    out.write(outDate);
    System.out.print(outDate);
   }
   System.out.println();
   out.close();
  }catch(IOException e) {
   e.printStackTrace();

  }
 }

}

package pipeInputOutput1;
import java.io.IOException;
import java.io.PipedReader;
//字符输入流
public class ReadDate {
 public void readMethod(PipedReader in) {

  try {
   System.out.println("read:");
   char[] byteArray=new char[20];
   int readLength=in.read(byteArray);
   while(readLength!=-1) {
    String newDate=new String(byteArray,0,readLength);
    System.out.print(newDate);
    readLength=in.read(byteArray);
   }
   System.out.println();
   in.close();
  } catch (IOException e) {
   e.printStackTrace();
  }
 }

}

package pipeInputOutput1;
import java.io.PipedWriter;
//输出流线程
public class WriteThread extends Thread {
 private WriteDate write;
 private PipedWriter out;
 public WriteThread(WriteDate write,PipedWriter out) {
  super();
  this.write=write;
  this.out=out;
 }

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

}

package pipeInputOutput1;
import java.io.PipedReader;
//输入流线程
public class ReadThread extends Thread{
 private ReadDate read;
 private PipedReader in;
 public ReadThread(ReadDate read,PipedReader in) {
  super();
  this.read=read;
  this.in=in;
 }
 public void run() {
  read.readMethod(in);
 }

}

package pipeInputOutput1;
import java.io.IOException;
import java.io.PipedReader;
import java.io.PipedWriter;
//测试方法
public class run {
 public static void main(String[] args) {
  try {
   WriteDate write=new WriteDate();
   ReadDate read=new ReadDate();

   PipedWriter out=new PipedWriter();
   PipedReader in=new PipedReader();
   //连接输出流与输入流
   out.connect(in);
   //in.connect(out);
   ReadThread threadread=new ReadThread(read,in);
   threadread.start();

   Thread.sleep(2000);
   WriteThread threadwrite=new WriteThread(write,out);
   threadwrite.start();
  } catch (IOException e) {
   e.printStackTrace();
  } catch (InterruptedException e) {
   e.printStackTrace();
  }
 }
}

字符流额字节流大同小异，上面的例子中字符流不需要创建字节数组而已。

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