PipedWriter和PipedReader源码分析_动力节点Java学院整理

package java.io;
 public class PipedWriter extends Writer {
   // 与PipedWriter通信的PipedReader对象
   private PipedReader sink;
   // PipedWriter的关闭标记
   private boolean closed = false;
   // 构造函数，指定配对的PipedReader
   public PipedWriter(PipedReader snk) throws IOException {
     connect(snk);
   }
   // 构造函数
   public PipedWriter() {
   }
   // 将“PipedWriter” 和 “PipedReader”连接。
   public synchronized void connect(PipedReader snk) throws IOException {
     if (snk == null) {
       throw new NullPointerException();
     } else if (sink != null || snk.connected) {
       throw new IOException("Already connected");
     } else if (snk.closedByReader || closed) {
       throw new IOException("Pipe closed");
     }
     sink = snk;
     snk.in = -1;
     snk.out = 0;
     // 设置“PipedReader”和“PipedWriter”为已连接状态
     // connected是PipedReader中定义的，用于表示“PipedReader和PipedWriter”是否已经连接
     snk.connected = true;
   }
   // 将一个字符c写入“PipedWriter”中。
   // 将c写入“PipedWriter”之后，它会将c传输给“PipedReader”
   public void write(int c) throws IOException {
     if (sink == null) {
       throw new IOException("Pipe not connected");
     }
     sink.receive(c);
   }
   // 将字符数组b写入“PipedWriter”中。
   // 将数组b写入“PipedWriter”之后，它会将其传输给“PipedReader”
   public void write(char cbuf[], int off, int len) throws IOException {
     if (sink == null) {
       throw new IOException("Pipe not connected");
     } else if ((off | len | (off + len) | (cbuf.length - (off + len))) < ) {
       throw new IndexOutOfBoundsException();
     }
     sink.receive(cbuf, off, len);
   }
   // 清空“PipedWriter”。
   // 这里会调用“PipedReader”的notifyAll()；
   // 目的是让“PipedReader”放弃对当前资源的占有，让其它的等待线程(等待读取PipedWriter的线程)读取“PipedWriter”的值。
   public synchronized void flush() throws IOException {
     if (sink != null) {
       if (sink.closedByReader || closed) {
         throw new IOException("Pipe closed");
       }
       synchronized (sink) {
         sink.notifyAll();
       }
     }
   }
   // 关闭“PipedWriter”。
   // 关闭之后，会调用receivedLast()通知“PipedReader”它已经关闭。
   public void close() throws IOException {
     closed = true;
     if (sink != null) {
       sink.receivedLast();
     }
   }
 }

package java.io;
  public class PipedReader extends Reader {
    // “PipedWriter”是否关闭的标记
    boolean closedByWriter = false;
    // “PipedReader”是否关闭的标记
    boolean closedByReader = false;
    // “PipedReader”与“PipedWriter”是否连接的标记
    // 它在PipedWriter的connect()连接函数中被设置为true
   boolean connected = false;
   Thread readSide;  // 读取“管道”数据的线程
   Thread writeSide;  // 向“管道”写入数据的线程
   // “管道”的默认大小
  private static final int DEFAULT_PIPE_SIZE = 1024;
   // 缓冲区
   char buffer[];
   //下一个写入字符的位置。in==out代表满，说明“写入的数据”全部被读取了。
   int in = -;
   //下一个读取字符的位置。in==out代表满，说明“写入的数据”全部被读取了。
   int out = ;
   // 构造函数：指定与“PipedReader”关联的“PipedWriter”
   public PipedReader(PipedWriter src) throws IOException {
     this(src, DEFAULT_PIPE_SIZE);
   }
   // 构造函数：指定与“PipedReader”关联的“PipedWriter”，以及“缓冲区大小”
   public PipedReader(PipedWriter src, int pipeSize) throws IOException {
     initPipe(pipeSize);
     connect(src);
   }
   // 构造函数：默认缓冲区大小是1024字符
   public PipedReader() {
     initPipe(DEFAULT_PIPE_SIZE);
   }
   // 构造函数：指定缓冲区大小是pipeSize
   public PipedReader(int pipeSize) {
     initPipe(pipeSize);
   }
   // 初始化“管道”：新建缓冲区大小
   private void initPipe(int pipeSize) {
    if (pipeSize <= 0) {
       throw new IllegalArgumentException("Pipe size <= 0");
     }
     buffer = new char[pipeSize];
   }
   // 将“PipedReader”和“PipedWriter”绑定。
   // 实际上，这里调用的是PipedWriter的connect()函数
   public void connect(PipedWriter src) throws IOException {
     src.connect(this);
   }
   // 接收int类型的数据b。
   // 它只会在PipedWriter的write(int b)中会被调用
   synchronized void receive(int c) throws IOException {
     // 检查管道状态
     if (!connected) {
       throw new IOException("Pipe not connected");
     } else if (closedByWriter || closedByReader) {
       throw new IOException("Pipe closed");
     } else if (readSide != null && !readSide.isAlive()) {
       throw new IOException("Read end dead");
     }
     // 获取“写入管道”的线程
     writeSide = Thread.currentThread();
     // 如果“管道中被读取的数据，等于写入管道的数据”时，
    // 则每隔1000ms检查“管道状态”，并唤醒管道操作：若有“读取管道数据线程被阻塞”，则唤醒该线程。
     while (in == out) {
       if ((readSide != null) && !readSide.isAlive()) {
         throw new IOException("Pipe broken");
       }
       /* full: kick any waiting readers */
       notifyAll();
       try {
        wait(1000);
       } catch (InterruptedException ex) {
         throw new java.io.InterruptedIOException();
       }
     }
    if (in < 0) {
     in = 0;
      out = 0;
     }
     buffer[in++] = (char) c;
     if (in >= buffer.length) {
      in = 0;
     }
   }
   // 接收字符数组b。
   synchronized void receive(char c[], int off, int len) throws IOException {
     while (--len >= ) {
      receive(c[off++]);
     }
   }
   // 当PipedWriter被关闭时，被调用
   synchronized void receivedLast() {
     closedByWriter = true;
     notifyAll();
   }
   // 从管道(的缓冲)中读取一个字符，并将其转换成int类型
   public synchronized int read() throws IOException {
     if (!connected) {
       throw new IOException("Pipe not connected");
     } else if (closedByReader) {
       throw new IOException("Pipe closed");
     } else if (writeSide != null && !writeSide.isAlive()
          && !closedByWriter && (in < )) {
       throw new IOException("Write end dead");
     }
     readSide = Thread.currentThread();
    int trials = 2;
    while (in < 0) {
       if (closedByWriter) {
         /* closed by writer, return EOF */
         return -1;
       }
       if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < )) {
         throw new IOException("Pipe broken");
       }
       /* might be a writer waiting */
       notifyAll();
       try {
        wait(1000);
       } catch (InterruptedException ex) {
         throw new java.io.InterruptedIOException();
       }
     }
     int ret = buffer[out++];
     if (out >= buffer.length) {
      out = 0;
     }
     if (in == out) {
       /* now empty */
      in = -1;
     }
     return ret;
   }
   // 从管道(的缓冲)中读取数据，并将其存入到数组b中
   public synchronized int read(char cbuf[], int off, int len) throws IOException {
     if (!connected) {
       throw new IOException("Pipe not connected");
     } else if (closedByReader) {
       throw new IOException("Pipe closed");
     } else if (writeSide != null && !writeSide.isAlive()
         && !closedByWriter && (in < 0)) {
       throw new IOException("Write end dead");
     }
    if ((off < 0) || (off > cbuf.length) || (len < 0) ||
      ((off + len) > cbuf.length) || ((off + len) < 0)) {
       throw new IndexOutOfBoundsException();
     } else if (len == 0) {
      return 0;
     }
     /* possibly wait on the first character */
     int c = read();
    if (c < 0) {
      return -1;
     }
     cbuf[off] = (char)c;
    int rlen = 1;
    while ((in >= 0) && (--len > 0)) {
       cbuf[off + rlen] = buffer[out++];
       rlen++;
       if (out >= buffer.length) {
       out = 0;
       }
       if (in == out) {
         /* now empty */
         in = -;
       }
     }
     return rlen;
   }
   // 是否能从管道中读取下一个数据
   public synchronized boolean ready() throws IOException {
     if (!connected) {
       throw new IOException("Pipe not connected");
     } else if (closedByReader) {
       throw new IOException("Pipe closed");
     } else if (writeSide != null && !writeSide.isAlive()
          && !closedByWriter && (in < )) {
       throw new IOException("Write end dead");
     }
    if (in < 0) {
       return false;
     } else {
       return true;
     }
   }
   // 关闭PipedReader
   public void close() throws IOException {
     in = -;
     closedByReader = true;
   }
 }

 import java.io.IOException;  
 import java.io.PipedReader;  
 @SuppressWarnings("all")  
 /** 
  * 接收者线程 
  */  
 public class Receiver extends Thread {  
   // 管道输入流对象。
   // 它和“管道输出流(PipedWriter)”对象绑定，
   // 从而可以接收“管道输出流”的数据，再让用户读取。
   private PipedReader in = new PipedReader();  
   // 获得“管道输入流对象”
   public PipedReader getReader(){  
     return in;  
   }  
   @Override
   public void run(){  
     readMessageOnce() ;
     //readMessageContinued() ;
   }
   // 从“管道输入流”中读取次数据
   public void readMessageOnce(){  
     // 虽然buf的大小是2048个字符，但最多只会从“管道输入流”中读取1024个字符。
    // 因为，“管道输入流”的缓冲区大小默认只有1024个字符。
     char[] buf = new char[2048];  
     try {  
       int len = in.read(buf);  
      System.out.println(new String(buf,0,len));  
       in.close();  
     } catch (IOException e) {  
       e.printStackTrace();  
     }  
   }
   // 从“管道输入流”读取>1024个字符时，就停止读取
  public void readMessageContinued(){
    int total=0;
     while(true) {
       char[] buf = new char[];
       try {
         int len = in.read(buf);
         total += len;
         System.out.println(new String(buf,,len));
        // 若读取的字符总数>1024，则退出循环。
       if (total > 1024)
           break;
       } catch (IOException e) {
         e.printStackTrace();
       }
     }
     try {
       in.close(); 
     } catch (IOException e) {  
       e.printStackTrace();  
     }  
   }  
 }
 
Sender.java的代码如下：
 
 import java.io.IOException;  
  import java.io.PipedWriter;  
 @SuppressWarnings("all")
 /** 
  * 发送者线程 
  */  
 public class Sender extends Thread {  
   // 管道输出流对象。
   // 它和“管道输入流(PipedReader)”对象绑定，
   // 从而可以将数据发送给“管道输入流”的数据，然后用户可以从“管道输入流”读取数据。
   private PipedWriter out = new PipedWriter();
   // 获得“管道输出流”对象
   public PipedWriter getWriter(){
     return out;
   }  
   @Override
   public void run(){  
     writeShortMessage();
     //writeLongMessage();
   }  
   // 向“管道输出流”中写入一则较简短的消息："this is a short message" 
   private void writeShortMessage() {
     String strInfo = "this is a short message" ;
     try {
       out.write(strInfo.toCharArray());
       out.close();  
     } catch (IOException e) {  
       e.printStackTrace();  
     }  
   }
   // 向“管道输出流”中写入一则较长的消息
   private void writeLongMessage() {
     StringBuilder sb = new StringBuilder();
    // 通过for循环写入1020个字符
     for (int i=0; i<102; i++)
      sb.append("0123456789");
    // 再写入26个字符。
    sb.append("abcdefghijklmnopqrstuvwxyz");
    // str的总长度是1020+26=1046个字符
    String str = sb.toString();
    try {
      // 将1046个字符写入到“管道输出流”中
       out.write(str);
       out.close();
     } catch (IOException e) {
       e.printStackTrace();
     }
   }
 }
 

 import java.io.PipedReader;
 import java.io.PipedWriter;
 import java.io.IOException;
 @SuppressWarnings("all")  
 /** 
  * 管道输入流和管道输出流的交互程序
  */  
 public class PipeTest {  
   public static void main(String[] args) {  
    Sender t1 = new Sender();  
   Receiver t2 = new Receiver();  
    PipedWriter out = t1.getWriter();  
     PipedReader in = t2.getReader();  
     try {  
       //管道连接。下面句话的本质是一样。
       //out.connect(in);  
       in.connect(out);  
       /** 
       * Thread类的START方法： 
       * 使该线程开始执行；Java 虚拟机调用该线程的 run 方法。  
       * 结果是两个线程并发地运行；当前线程（从调用返回给 start 方法）和另一个线程（执行其 run 方法）。  
       * 多次启动一个线程是非法的。特别是当线程已经结束执行后，不能再重新启动。  
       */
       t.start();
       t.start();
     } catch (IOException e) {
       e.printStackTrace();
     }
   }
 }

this is a short message

public void write(char cbuf[]) throws IOException {
  write(cbuf, 0, cbuf.length);
}

public void run(){  
  writeShortMessage();
  //writeLongMessage();
}

public void run(){  
  //writeShortMessage();
  writeLongMessage();
}

while (in == out) {
  if ((readSide != null) && !readSide.isAlive()) {
    throw new IOException("Pipe broken");
  }
  /* full: kick any waiting readers */
  notifyAll();
  try {
    wait(1000);
  } catch (InterruptedException ex) {
    throw new java.io.InterruptedIOException();
  }
}

public void run(){  
  readMessageOnce() ;
  //readMessageContinued() ;
}

public void run(){  
  //readMessageOnce() ;
  readMessageContinued() ;
}