Java 日看一类（43）之IO包中的PipedOutputStream类

该类继承自OutputStream

引入了IO包（本来就是这个包里的，引得没看懂）

该类的类头注释如下：

/**
 * A piped output stream can be connected to a piped input stream
 * to create a communications pipe. The piped output stream is the
 * sending end of the pipe. Typically, data is written to a
 * <code>PipedOutputStream</code> object by one thread and data is
 * read from the connected <code>PipedInputStream</code> by some
 * other thread. Attempting to use both objects from a single thread
 * is not recommended as it may deadlock the thread.
 * The pipe is said to be <a name=BROKEN> <i>broken</i> </a> if a
 * thread that was reading data bytes from the connected piped input
 * stream is no longer alive.
 *
 * @author  James Gosling
 * @see     java.io.PipedInputStream
 * @since   JDK1.0
 */

大意如下：

管道输出流可以与管道输入流连接成可用的通信管道

管道输出流是管道的发送段

典型情况下，数据会被某线程写入管道输出流，然后会被与其链接的管道输入流通过其他线程读出

建议使用这两个类时不要使用单线程（可能会造成死锁）

如果某个线程正从连接的管道输入流中读取数据字节，但该线程不再处于活动状态，则该管道被视为断裂

该类含有如下的成员变量：

与其相连接的管道输入流

private PipedInputStream sink;

该类含有如下的成员方法：

构造函数（与给定的输入流相链接

public PipedOutputStream(PipedInputStream snk)  throws IOException {
    connect(snk);
}

构造函数（空，不链接

public PipedOutputStream() {
}

与输入流相链接

public synchronized void connect(PipedInputStream snk) throws IOException {
    if (snk == null) {//输入流有效性
        throw new NullPointerException();
    } else if (sink != null || snk.connected) {//自己或给定流已链接
        throw new IOException("Already connected");
    }
    sink = snk;//绑定对象
    snk.in = -1;//缓存空间偏移量修改
    snk.out = 0;
    snk.connected = true;
}

写入一个字节

public void write(int b)  throws IOException {
    if (sink == null) {
        throw new IOException("Pipe not connected");
    }
    sink.receive(b);//输入流接收
}

写入一个字节数组

public void write(byte b[], int off, int len) throws IOException {
    if (sink == null) {//链接检查
        throw new IOException("Pipe not connected");
    } else if (b == null) {//数组有效性检查
        throw new NullPointerException();
    } else if ((off < 0) || (off > b.length) || (len < 0) ||//下标有效性
               ((off + len) > b.length) || ((off + len) < 0)) {
        throw new IndexOutOfBoundsException();
    } else if (len == 0) {
        return;
    }
    sink.receive(b, off, len);
}

刷新输出流（写出底层流缓冲的数据，并且唤醒沉睡的reader线程

public synchronized void flush() throws IOException {
    if (sink != null) {
        synchronized (sink) {//保证控制权
            sink.notifyAll();//唤起reader线程读取缓冲数据
        }
    }
}

关闭管道（释放资源

public void close()  throws IOException {
    if (sink != null) {
        sink.receivedLast();//关闭了写入端，并且唤醒读取线程读取剩余缓存
    }
}

该类的操作主要都是通过调用PipedInputStream类，相当于把大部分操作都封装到输入流里了，所以在学习这个之前建议先去学习PipedInputSream

Java 日看一类（43）之IO包中的PipedOutputStream类

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