文章目录

• 字节流
• • InputStream
  • • FilterInputStream
    • ByteArrayInputStream
    • //todo FileInputStream
    • BufferInputStream
    • PipedInputStream
    • //todo ObjectInputStream
  • OutputStream
  • • //todo FileOutputStream
    • BufferedOutputStream
    • PipedOutputStream
    • //todo ObjectOutputStream
• 字符流
• • Reader
  • • //todo FileReader
    • BufferedReader
  • Writer
  • • //todo FileWriter
    • //todo BufferWriter
• 转换流
• • //todo InputStreamReader
  • //todo OutputStreamWriter

字节流

InputStream

public abstract class InputStream implements Closeable {
    //最大可跳过字节数
    private static final int MAX_SKIP_BUFFER_SIZE = 2048;
  public int read(byte b[], int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if (off < 0 || len < 0 || len > b.length - off) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }
        //读取一字节数据
        int c = read();
        //到达文件的末端返回-1
        if (c == -1) {
            return -1;
        }
        //赋值
        b[off] = (byte)c;
        //一个字节一个字节读取,填充到b数组
        int i = 1;
        try {
            for (; i < len ; i++) {
                c = read();
                if (c == -1) {
                    break;
                }
                b[off + i] = (byte)c;
            }
        } catch (IOException ee) {
        }
        return i;
    }
 public long skip(long n) throws IOException {
        long remaining = n;
        int nr;
        if (n <= 0) {
            return 0;
        }
        //最大创建MAX_SKIP_BUFFER_SIZE大小数组
        int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
        byte[] skipBuffer = new byte[size];
        //使用循环,尽量读取remaining大小数据
        while (remaining > 0) {
            nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
            //读到流的末端，则返回
            if (nr < 0) {
                break;
            }
            remaining -= nr;
        }
        return n - remaining;
    }
 //返回默认值
    public int available() throws IOException {
        return 0;
    }
  //标记一个位置,用于reset,当超过readlimit,则标记位置失效
    public synchronized void mark(int readlimit) {
    }
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }
    //是否支持标记,默认不支持
    public boolean markSupported() {
        return false;
    }

FilterInputStream

public class FilterInputStream extends InputStream {
    //装饰器的代码特征：被装饰的对象一般是装饰器的成员变量
    protected volatile InputStream in; //将要被装饰的字节输入流
    protected FilterInputStream(InputStream in) {
       //通过构造方法传入此被装饰的流
        this.in = in;
     }
    //下面这些方法，完成最小的装饰――0装饰，只是调用被装饰流的方法而已
    public int read() throws IOException {
        return in.read();
    }
    public int read(byte b[]) throws IOException {
        return read(b, 0, b.length);
     }
    public int read(byte b[], int off, int len) throws IOException {
        return in.read(b, off, len);
     }
    public long skip(long n) throws IOException {
        return in.skip(n);
    }
    public int available() throws IOException {
        return in.available();
    }
    public void close() throws IOException {
        in.close();
    }
    public synchronized void mark(int readlimit) {
        in.mark(readlimit);
     }
    public synchronized void reset() throws IOException {
        in.reset();
    }
    public boolean markSupported() {
        return in.markSupported();
    }
}

ByteArrayInputStream

将内存中的数组装饰成InputStrean

public
class ByteArrayInputStream extends InputStream {
    //包装的字节数组
    protected byte buf[];
    //读取位置
    protected int pos;
    //标记位置
    protected int mark = 0;
    //数组长度
    protected int count;
    public ByteArrayInputStream(byte buf[]) {
        //装饰的数组
        this.buf = buf;
        //设置位置和长度
        this.pos = 0;
        this.count = buf.length;
    }
    public ByteArrayInputStream(byte buf[], int offset, int length) {
        this.buf = buf;
        this.pos = offset;
        this.count = Math.min(offset + length, buf.length);
        this.mark = offset;
    }
    public synchronized int read() {
        return (pos < count) ? (buf[pos++] & 0xff) : -1;
    }
    public synchronized int read(byte b[], int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        } else if (off < 0 || len < 0 || len > b.length - off) {
            throw new IndexOutOfBoundsException();
        }
        //超过范围,返回-1
        if (pos >= count) {
            return -1;
        }
        //查看剩下可读字节大小
        int avail = count - pos;
        //超过限制,则默认查询剩下可读字节数
        if (len > avail) {
            len = avail;
        }
        if (len <= 0) {
            return 0;
        }
        System.arraycopy(buf, pos, b, off, len);
        pos += len;
        return len;
    }
    public synchronized long skip(long n) {
        long k = count - pos;
        if (n < k) {
            k = n < 0 ? 0 : n;
        }
        pos += k;
        return k;
    }
    public synchronized int available() {
        return count - pos;
    }
    public boolean markSupported() {
        return true;
    }
    public void mark(int readAheadLimit) {
        mark = pos;
    }
    /**
     * Resets the buffer to the marked position.  The marked position
     * is 0 unless another position was marked or an offset was specified
     * in the constructor.
     */
    public synchronized void reset() {
        pos = mark;
    }
    public void close() throws IOException {
    //什么操作都没有
    }
}

//todo FileInputStream

BufferInputStream

public
class BufferedInputStream extends FilterInputStream {
    //默认缓冲区大小
    private static int DEFAULT_BUFFER_SIZE = 8192;
    //缓冲区最大扩展容量
    private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
    //缓冲数组
    protected volatile byte buf[];
    //用于CAS 修改数组
    private static final
        AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
        AtomicReferenceFieldUpdater.newUpdater
        (BufferedInputStream.class,  byte[].class, "buf");
    //缓冲区读取的个数
    protected int count;
    //当前读取位置
    protected int pos;
    //标记当前pos,用于reset,则重新开始从markpos读取
    protected int markpos = -1;
    //读取内容超过limit,markpos失效
    protected int marklimit;
    private InputStream getInIfOpen() throws IOException {
        //获取封装输入流
        InputStream input = in;
        if (input == null)
            throw new IOException("Stream closed");
        return input;
    }
    private byte[] getBufIfOpen() throws IOException {
        ///获取缓冲区数组
        byte[] buffer = buf;
        if (buffer == null)
            throw new IOException("Stream closed");
        return buffer;
    }
    public BufferedInputStream(InputStream in) {
        //默认缓冲数组大小8192
        this(in, DEFAULT_BUFFER_SIZE);
    }
    public BufferedInputStream(InputStream in, int size) {
        super(in);
        if (size <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
        buf = new byte[size];
    }
    private void fill() throws IOException {
        //获取缓冲数组
        byte[] buffer = getBufIfOpen();
        if (markpos < 0)
            pos = 0;            /* no mark: throw away the buffer */
        //设置了标记位置,以及当前读取的位置超过缓存数据最大长度
        else if (pos >= buffer.length)  /* no room left in buffer */
            //这一步相当于把markpos右边数据全部挪移到左边,因为标记的位置指不定需要reset,所以相当于保存一个进度点
            if (markpos > 0) {
      /* can throw away early part of the buffer */
                int sz = pos - markpos;
                //将buffer数组从标记位置开始,复制sz个数到buffer
                System.arraycopy(buffer, markpos, buffer, 0, sz);
                //记录新的位置
                pos = sz;
                //标记位置回滚0
                markpos = 0;
            } else if (buffer.length >= marklimit) {
                //当buffer长度超过marklimit时,mark失效
                markpos = -1;   /* buffer got too big, invalidate mark */
                pos = 0;        /* drop buffer contents */
            } else if (buffer.length >= MAX_BUFFER_SIZE) {
                //说明无法继续扩容缓冲数组容量了
                throw new OutOfMemoryError("Required array size too large");
            } else {
                /* grow buffer */
                //扩容一倍容量
                int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
                        pos * 2 : MAX_BUFFER_SIZE;
                //太大则为marklimit大小
                if (nsz > marklimit)
                    nsz = marklimit;
                byte nbuf[] = new byte[nsz];
                //将buffer数据copy扩容后的nbuf
                System.arraycopy(buffer, 0, nbuf, 0, pos);
                if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
                    // Can't replace buf if there was an async close.
                    // Note: This would need to be changed if fill()
                    // is ever made accessible to multiple threads.
                    // But for now, the only way CAS can fail is via close.
                    // assert buf == null;
                    throw new IOException("Stream closed");
                }
                buffer = nbuf;
            }
        //设置下步没读取到数据,设置默认值
        count = pos;
        //从流中读取数据到缓冲数组
        int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
        //读取到数据,则记录最新的缓冲数组大小
        if (n > 0)
            count = n + pos;
    }
    public synchronized int read() throws IOException {
        //当前读取位置>=缓冲区最大容量,则重新从输入流获取数据
        if (pos >= count) {
            fill();
            if (pos >= count)
                return -1;
        }
        //缓冲读取一个字节
        return getBufIfOpen()[pos++] & 0xff;
    }
    private int read1(byte[] b, int off, int len) throws IOException {
        //余下缓冲数组容量=buf数组长度-当前读取位置
        int avail = count - pos;
        //初次读取,又或者读取完缓冲数组
        if (avail <= 0) {
            //len超过缓冲数组的长度,则直接返回，不缓存
            if (len >= getBufIfOpen().length && markpos < 0) {
                return getInIfOpen().read(b, off, len);
            }
            //填充到缓冲数组
            fill();
            //返回读取个数
            avail = count - pos;
            if (avail <= 0) return -1;
        }
        //边界检查,最多只能获取缓冲数组最大容量的数据
        int cnt = (avail < len) ? avail : len;
        //缓冲数组获取数据
        System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
        //记录当前读取位置
        pos += cnt;
        return cnt;
    }
    public synchronized int read(byte b[], int off, int len)
        throws IOException
    {
        //判断buffer是否打开
        getBufIfOpen(); // Check for closed stream
        //off=0 len=1024.则值为1024
        //判断off+len < b.length 则越界异常
        //也就是说从off开始读取len长度.
        if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }
        //记录读取的总字节数
        int n = 0;
        for (;;) {
            //读取到b数组,返回读取个数
            int nread = read1(b, off + n, len - n);
            //说明没读取到,则直接返回
            if (nread <= 0)
                return (n == 0) ? nread : n;
            //累加读取字节数
            n += nread;
            //读取的总字节数＞=读取长度,则直接返回
            if (n >= len)
                return n;
            // if not closed but no bytes available, return
            InputStream input = in;
            //虽然读取的字节数<=读取长度,但是如果可以读取的字节数预估读完了,则直接返回
            if (input != null && input.available() <= 0)
                return n;
        }
    }
    public synchronized long skip(long n) throws IOException {
        getBufIfOpen(); // Check for closed stream
        if (n <= 0) {
            return 0;
        }
        //可以跳过的最大范围
        long avail = count - pos;
        //说明尚未读取,又或者已经读取填充完整个缓冲区
        if (avail <= 0) {
            // If no mark position set then don't keep in buffer
            //尚未标记位置,则直接操作输入流跳过n
            if (markpos <0)
                return getInIfOpen().skip(n);
            // Fill in buffer to save bytes for reset
            //填充缓存数组
            fill();
            //获取填充之后的可跳过范围
            avail = count - pos;
            //依旧没,则返回
            if (avail <= 0)
                return 0;
        }
        //跳过的最大不能超过最大可以跳过的范围
        long skipped = (avail < n) ? avail : n;
        //记录新的位置
        pos += skipped;
        return skipped;
    }
    //该方法的返回值为缓存中的可读字节数目加流中可读字节数目的和
    public synchronized int available() throws IOException {
        int n = count - pos;
        int avail = getInIfOpen().available();
        return n > (Integer.MAX_VALUE - avail)
                    ? Integer.MAX_VALUE
                    : n + avail;
    }
    public synchronized void mark(int readlimit) {
        //标记位置无效之前可以读取的最大字节数
        marklimit = readlimit;
        //标记此输入流中的当前位置
        markpos = pos;
    }
    public synchronized void reset() throws IOException {
        getBufIfOpen(); // Cause exception if closed
        if (markpos < 0)
            throw new IOException("Resetting to invalid mark");
        pos = markpos;
    }
    //该流和ByteArrayInputStream一样都支持mark
    public boolean markSupported() {
        return true;
    }
    public void close() throws IOException {
        byte[] buffer;
        while ( (buffer = buf) != null) {
            //CAS,清空缓冲流
            if (bufUpdater.compareAndSet(this, buffer, null)) {
                InputStream input = in;
                in = null;
                if (input != null)
                    input.close();
                return;
            }
        }
    }
}

PipedInputStream

public class PipedInputStream extends InputStream {
    //分别标记当前读管道,写管道的状态
    boolean closedByWriter = false;
    volatile boolean closedByReader = false;
    //标记是否连接到写管道
    boolean connected = false;
        //读写2个线程
    Thread readSide;
    Thread writeSide;
    //默认管道缓冲区大小
    private static final int DEFAULT_PIPE_SIZE = 1024;
    protected static final int PIPE_SIZE = DEFAULT_PIPE_SIZE;
    protected byte buffer[];
    //下一个写入字节位置   in=out则说明满了
    protected int in = -1;
    //下一个读取字节位置
    protected int out = 0;
    public PipedInputStream(PipedOutputStream src) throws IOException {
        this(src, DEFAULT_PIPE_SIZE);
    }
    public PipedInputStream(PipedOutputStream src, int pipeSize)
            throws IOException {
        //初始化缓冲区大小,默认大小1024
         initPipe(pipeSize);
         //将当前对象传入PipedOutputStream
         connect(src);
    }
    public PipedInputStream() {
        //初始化缓冲区大小,默认大小1024
        initPipe(DEFAULT_PIPE_SIZE);
    }
    public PipedInputStream(int pipeSize) {
        //初始化指定大小的缓冲区
        initPipe(pipeSize);
    }
    private void initPipe(int pipeSize) {
        //初始化指定大小管道缓冲区
         if (pipeSize <= 0) {
            throw new IllegalArgumentException("Pipe Size <= 0");
         }
         buffer = new byte[pipeSize];
    }
    public void connect(PipedOutputStream src) throws IOException {
        //管道连接
        src.connect(this);
    }
    //接受output发送过来的数据
    protected synchronized void receive(int b) throws IOException {
        checkStateForReceive();
        //获取当前线程
        writeSide = Thread.currentThread();
        //读满,则等待,通知其他读线程,我要开始写了
        if (in == out)
            awaitSpace();
        //读满或初次读取,则重置下标
        if (in < 0) {
            in = 0;
            out = 0;
        }
        //写入数据
        buffer[in++] = (byte)(b & 0xFF);
        //超过边界则从0开始
        if (in >= buffer.length) {
            in = 0;
        }
    }
    synchronized void receive(byte b[], int off, int len)  throws IOException {
        //检查读写管道状态是否正常开放
        checkStateForReceive();
        writeSide = Thread.currentThread();
        int bytesToTransfer = len;
        while (bytesToTransfer > 0) {
            //读满,则等待,通知其他读线程,我要开始写了
            if (in == out)
                awaitSpace();
            int nextTransferAmount = 0;
            //如果还有空间可以读取,则获取最大可读取大小
            if (out < in) {
                nextTransferAmount = buffer.length - in;
            } else if (in < out) {
                //读满或者初次读取则重置
                if (in == -1) {
                    in = out = 0;
                    nextTransferAmount = buffer.length - in;
                } else {
                //读到这里说明in走了一圈,重置为0了
                    nextTransferAmount = out - in;
                }
            }
            //读取空间足够
            if (nextTransferAmount > bytesToTransfer)
                nextTransferAmount = bytesToTransfer;
            assert(nextTransferAmount > 0);
            //写入范围数据到buffer
            System.arraycopy(b, off, buffer, in, nextTransferAmount);
            //记录剩下还需要写入的空间
            bytesToTransfer -= nextTransferAmount;
            off += nextTransferAmount;
            in += nextTransferAmount;
            //写入超限,重置
            if (in >= buffer.length) {
                in = 0;
            }
        }
    }
    private void checkStateForReceive() throws IOException {
        //当前是否连接
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByWriter || closedByReader) {
            //当前读写管道是否关闭了
            throw new IOException("Pipe closed");
        } else if (readSide != null && !readSide.isAlive()) {
            //当前线程死了
            throw new IOException("Read end dead");
        }
    }
    private void awaitSpace() throws IOException {
        while (in == out) {
            //检查读写管道状态是否正常开放
            checkStateForReceive();
            /* full: kick any waiting readers */
            //通知
            notifyAll();
            try {
                //等待
                wait(1000);
            } catch (InterruptedException ex) {
                throw new java.io.InterruptedIOException();
            }
        }
    }
    synchronized void receivedLast() {
        //标记写管道流关闭
        closedByWriter = true;
        //通知所有等待的线程
        notifyAll();
    }
    public synchronized int read()  throws IOException {
        //校验当前线程是否正常连接
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
            //当前读管道是否关闭
            throw new IOException("Pipe closed");
        } else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            //写线程是否存活,以及是否关闭了写流
            throw new IOException("Write end dead");
        }
        readSide = Thread.currentThread();
        int trials = 2;
        //等待写入
        while (in < 0) {
            //写入流关闭,则返回-1
            if (closedByWriter) {
                /* closed by writer, return EOF */
                return -1;
            }
            //写线程已经不存活了,则抛异常
            if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < 0)) {
                throw new IOException("Pipe broken");
            }
            /* might be a writer waiting */
            //通知线程,开始读了
            notifyAll();
            try {
                //等待
                wait(1000);
            } catch (InterruptedException ex) {
                throw new java.io.InterruptedIOException();
            }
        }
        //读入数据
        int ret = buffer[out++] & 0xFF;
        //读到缓冲区上限则重置
        if (out >= buffer.length) {
            out = 0;
        }
        //读满则重置
        if (in == out) {
            /* now empty */
            in = -1;
        }
        return ret;
    }
    public synchronized int read(byte b[], int off, int len)  throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if (off < 0 || len < 0 || len > b.length - off) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }
        /* possibly wait on the first character */
        //尝试读取一个字节
        int c = read();
        //没数据则直接返回
        if (c < 0) {
            return -1;
        }
        b[off] = (byte) c;
        int rlen = 1;
        while ((in >= 0) && (len > 1)) {
            int available;
            //获取可读取的范围
            if (in > out) {
                available = Math.min((buffer.length - out), (in - out));
            } else {
                //执行到这里,说明in写了一圈了.
                available = buffer.length - out;
            }
            // A byte is read beforehand outside the loop
            //可读取的空间足够,则直接读取len-1长度
            if (available > (len - 1)) {
                available = len - 1;
            }
            System.arraycopy(buffer, out, b, off + rlen, available);
            out += available;
            rlen += available;
            len -= available;
            //读到缓冲区上限则重置
            if (out >= buffer.length) {
                out = 0;
            }
            //读满则重置
            if (in == out) {
                /* now empty */
                in = -1;
            }
        }
        return rlen;
    }
    public synchronized int available() throws IOException {
        //读满,或者第一次读取,则暂无字节可读取
        if(in < 0)
            return 0;
        else if(in == out)
            //读满,则重置范围
            return buffer.length;
        else if (in > out)
            //还在一圈范围内
            return in - out;
        else
            //读取一圈
            return in + buffer.length - out;
    }
    public void close()  throws IOException {
        //标记当前读流关闭
        closedByReader = true;
        synchronized (this) {
            in = -1;
        }
    }
}

//todo ObjectInputStream

OutputStream

public abstract class OutputStream implements Closeable, Flushable {
    public abstract void write(int b) throws IOException;
    public void write(byte b[]) throws IOException {
        write(b, 0, b.length);
    }
    public void write(byte b[], int off, int len) throws IOException {
        //非空,上下界限校验
        if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) ||
                   ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }
        //一个字节一个字节写入
        for (int i = 0 ; i < len ; i++) {
            write(b[off + i]);
        }
    }
    //刷新此输出流并强制任何缓冲的输出字节被写出。
    public void flush() throws IOException {
    }
    //关闭
    public void close() throws IOException {
    }
}

//todo FileOutputStream

BufferedOutputStream

Java IO中的管道为运行在同一个JVM中的两个线程提供了通信的能力。所以管道也可以作为数据源以及目标媒介

public
class BufferedOutputStream extends FilterOutputStream {
    //记录缓冲大小,默认8192
    protected byte buf[];
    //记录缓冲数据个数
    protected int count;
    public BufferedOutputStream(OutputStream out) {
        this(out, 8192);
    }
    public BufferedOutputStream(OutputStream out, int size) {
        //使用父类装饰outputStream
        super(out);
        if (size <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
        //创建缓冲数组,默认大小8192
        buf = new byte[size];
    }
    private void flushBuffer() throws IOException {
        //当缓冲数组有数据,则刷新到输出流中,重置数组长度
        if (count > 0) {
            out.write(buf, 0, count);
            count = 0;
        }
    }
    public synchronized void write(int b) throws IOException {
        //写入长度超过缓冲数组长度,则刷新一遍
        if (count >= buf.length) {
            flushBuffer();
        }
        //记录
        buf[count++] = (byte)b;
    }
    public synchronized void write(byte b[], int off, int len) throws IOException {
        //写入长度,超过缓冲数组长度,则刷新一遍,写入输出流
        if (len >= buf.length) {
            flushBuffer();
            out.write(b, off, len);
            return;
        }
        //写入长度,超过余下缓冲数组长度,刷新输出流一次
        if (len > buf.length - count) {
            flushBuffer();
        }
        //写入缓冲数组
        System.arraycopy(b, off, buf, count, len);
        ///累加数组记录字节数
        count += len;
    }
    public synchronized void flush() throws IOException {
        //缓冲数据写入输出流
        flushBuffer();
        //输出流刷新
        out.flush();
    }
}

PipedOutputStream

public
class PipedOutputStream extends OutputStream {
    private PipedInputStream sink;
    public PipedOutputStream(PipedInputStream snk)  throws IOException {
        //管道连接
        connect(snk);
    }
    public PipedOutputStream() {
    }
    public synchronized void connect(PipedInputStream snk) throws IOException {
        if (snk == null) {
            throw new NullPointerException();
        } else if (sink != null || snk.connected) {
            throw new IOException("Already connected");
        }
        sink = snk;
        //标记初次写入
        snk.in = -1;
        //读取起始位置
        snk.out = 0;
        //标记状态为连接
        snk.connected = true;
    }
    public void write(int b)  throws IOException {
        if (sink == null) {
            throw new IOException("Pipe not connected");
        }
        //往input写入数据
        sink.receive(b);
    }
    public void write(byte b[], int off, int len) throws IOException {
        if (sink == null) {
            throw new IOException("Pipe not connected");
        } else if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) ||
                   ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }
        //往input写入指定范围数据
        sink.receive(b, off, len);
    }
    //强制唤醒所有阻塞状态
    public synchronized void flush() throws IOException {
        if (sink != null) {
            synchronized (sink) {
                //通知其他
                sink.notifyAll();
            }
        }
    }
    public void close()  throws IOException {
        //标记当前管道已经关闭
        if (sink != null) {
            sink.receivedLast();
        }
    }
}

//todo ObjectOutputStream

字符流

Reader

public abstract class Reader implements Readable, Closeable {
    /**
     * The object used to synchronize operations on this stream.  For
     * efficiency, a character-stream object may use an object other than
     * itself to protect critical sections.  A subclass should therefore use
     * the object in this field rather than <tt>this</tt> or a synchronized
     * method.
     */
    //锁,默认当前对象
    protected Object lock;
    /**
     * Creates a new character-stream reader whose critical sections will
     * synchronize on the reader itself.
     */
    protected Reader() {
        this.lock = this;
    }
    /**
     * Creates a new character-stream reader whose critical sections will
     * synchronize on the given object.
     *
     * @param lock  The Object to synchronize on.
     */
    protected Reader(Object lock) {
        if (lock == null) {
            throw new NullPointerException();
        }
        this.lock = lock;
    }
    /**
     * Attempts to read characters into the specified character buffer.
     * The buffer is used as a repository of characters as-is: the only
     * changes made are the results of a put operation. No flipping or
     * rewinding of the buffer is performed.
     *
     * @param target the buffer to read characters into
     * @return The number of characters added to the buffer, or
     *         -1 if this source of characters is at its end
     * @throws IOException if an I/O error occurs
     * @throws NullPointerException if target is null
     * @throws java.nio.ReadOnlyBufferException if target is a read only buffer
     * @since 1.5
     */
    public int read(java.nio.CharBuffer target) throws IOException {
        int len = target.remaining();
        char[] cbuf = new char[len];
        int n = read(cbuf, 0, len);
        if (n > 0)
            target.put(cbuf, 0, n);
        return n;
    }
    /**
     * Reads a single character.  This method will block until a character is
     * available, an I/O error occurs, or the end of the stream is reached.
     *
     * <p> Subclasses that intend to support efficient single-character input
     * should override this method.
     *
     * @return     The character read, as an integer in the range 0 to 65535
     *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
     *             been reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read() throws IOException {
        //创建容量为一字符的数组
        char cb[] = new char[1];
        //读取一个字符
        if (read(cb, 0, 1) == -1)
            return -1;
        else
            return cb[0];
    }
    /**
     * Reads characters into an array.  This method will block until some input
     * is available, an I/O error occurs, or the end of the stream is reached.
     *
     * @param       cbuf  Destination buffer
     *
     * @return      The number of characters read, or -1
     *              if the end of the stream
     *              has been reached
     *
     * @exception   IOException  If an I/O error occurs
     */
    public int read(char cbuf[]) throws IOException {
        return read(cbuf, 0, cbuf.length);
    }
    /**
     * Reads characters into a portion of an array.  This method will block
     * until some input is available, an I/O error occurs, or the end of the
     * stream is reached.
     *
     * @param      cbuf  Destination buffer
     * @param      off   Offset at which to start storing characters
     * @param      len   Maximum number of characters to read
     *
     * @return     The number of characters read, or -1 if the end of the
     *             stream has been reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    abstract public int read(char cbuf[], int off, int len) throws IOException;
    /** Maximum skip-buffer size */
    private static final int maxSkipBufferSize = 8192;
    /** Skip buffer, null until allocated */
    private char skipBuffer[] = null;
    public long skip(long n) throws IOException {
        if (n < 0L)
            throw new IllegalArgumentException("skip value is negative");
        //默认最大只能跳过8192字节
        int nn = (int) Math.min(n, maxSkipBufferSize);
        synchronized (lock) {
            //新建记录跳过的字符
            if ((skipBuffer == null) || (skipBuffer.length < nn))
                skipBuffer = new char[nn];
            long r = n;
            while (r > 0) {
                int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
                if (nc == -1)
                    break;
                r -= nc;
            }
            return n - r;
        }
    }
    /**
     * Tells whether this stream is ready to be read.
     *
     * @return True if the next read() is guaranteed not to block for input,
     * false otherwise.  Note that returning false does not guarantee that the
     * next read will block.
     *
     * @exception  IOException  If an I/O error occurs
     */
    //告诉这个流是否准备好被读取。
    public boolean ready() throws IOException {
        return false;
    }
    /**
     * Tells whether this stream supports the mark() operation. The default
     * implementation always returns false. Subclasses should override this
     * method.
     *
     * @return true if and only if this stream supports the mark operation.
     */
    //不支持标记
    public boolean markSupported() {
        return false;
    }
    /**
     * Marks the present position in the stream.  Subsequent calls to reset()
     * will attempt to reposition the stream to this point.  Not all
     * character-input streams support the mark() operation.
     *
     * @param  readAheadLimit  Limit on the number of characters that may be
     *                         read while still preserving the mark.  After
     *                         reading this many characters, attempting to
     *                         reset the stream may fail.
     *
     * @exception  IOException  If the stream does not support mark(),
     *                          or if some other I/O error occurs
     */
    public void mark(int readAheadLimit) throws IOException {
        throw new IOException("mark() not supported");
    }
    /**
     * Resets the stream.  If the stream has been marked, then attempt to
     * reposition it at the mark.  If the stream has not been marked, then
     * attempt to reset it in some way appropriate to the particular stream,
     * for example by repositioning it to its starting point.  Not all
     * character-input streams support the reset() operation, and some support
     * reset() without supporting mark().
     *
     * @exception  IOException  If the stream has not been marked,
     *                          or if the mark has been invalidated,
     *                          or if the stream does not support reset(),
     *                          or if some other I/O error occurs
     */
    public void reset() throws IOException {
        throw new IOException("reset() not supported");
    }
    /**
     * Closes the stream and releases any system resources associated with
     * it.  Once the stream has been closed, further read(), ready(),
     * mark(), reset(), or skip() invocations will throw an IOException.
     * Closing a previously closed stream has no effect.
     *
     * @exception  IOException  If an I/O error occurs
     */
     abstract public void close() throws IOException;
}