java io

public abstract class InputStream implements Closeable {

    // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
    // use when skipping.
    private static final int MAX_SKIP_BUFFER_SIZE = 2048;

    public abstract int read() throws IOException;

    public int read(byte b[]) throws IOException {
        return read(b, 0, b.length);
    }

    // 模版方法
    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;
        }

      	// read()由子类实现
        int c = read();
        if (c == -1) {
            return -1;
        }
        b[off] = (byte)c;

        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;
        }

        int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
        byte[] skipBuffer = new byte[size];
        while (remaining > 0) {
            nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
            if (nr < 0) {
                break;
            }
            remaining -= nr;
        }

        return n - remaining;
    }

    public int available() throws IOException {
        return 0;
    }

    public void close() throws IOException {}
		
  	public synchronized void mark(int readlimit) {}

    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }

    public boolean markSupported() {
        return false;
    }

}

public
class FileInputStream extends InputStream
{
    public int read() throws IOException {
        return read0();  //本地方法
    }
    private native int read0() throws IOException;  //本地方法
    //读取字节数组，也是基于native方法
    public int read(byte b[], int off, int len) throws IOException {
        return readBytes(b, off, len);    //本地方法
    }
    //本地方法
    private native int readBytes(byte b[], int off, int len) throws IOException;
}

public
class FilterInputStream extends InputStream {
    /**
     * The input stream to be filtered.
     */
    protected volatile InputStream in;

    public int read(byte b[]) throws IOException {
      return read(b, 0, b.length);
    }
}

public
class BufferedInputStream extends FilterInputStream {
  protected volatile byte buf[];
    //读取单个字节
    public synchronized int read() throws IOException {
        if (pos >= count) {
            fill();    // buf 读取完毕，直接再从依赖的InputStream中读取字节数组，填充缓存
            if (pos >= count)
              return -1;
        }
        return getBufIfOpen()[pos++] & 0xff;  //buf有的话就直接返回
    }
    //填充buf
    private void fill() throws IOException {
        //...
        int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
        if (n > 0)
            count = n + pos;
    }
    // 读取字节数组
    public synchronized int read(byte b[], int off, int len)
        throws IOException
    {
        // ...
        int n = 0;
        for (;;) {
            int nread = read1(b, off + n, len - n);  //读取字节数组
            // ...
        }
    }
    //根据条件，有可能直接从输入流读取，有可能先填充buf，再从buf中获取
    private int read1(byte[] b, int off, int len) throws IOException {
        int avail = count - pos;
        if (avail <= 0) {
            if (len >= getBufIfOpen().length && markpos < 0) {
                return getInIfOpen().read(b, off, len);    //从输入流读取字节数组
            }
            fill();
            avail = count - pos;
            if (avail <= 0) return -1;
        }
        int cnt = (avail < len) ? avail : len;
        System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
        pos += cnt;
        return cnt;
    }
    //...

}

/**
 * A nexus for I/O operations.
 *
 * <p> A channel represents an open connection to an entity such as a hardware
 * device, a file, a network socket, or a program component that is capable of
 * performing one or more distinct I/O operations, for example reading or
 * writing.
 *
 * <p> A channel is either open or closed.  A channel is open upon creation,
 * and once closed it remains closed.  Once a channel is closed, any attempt to
 * invoke an I/O operation upon it will cause a {@link ClosedChannelException}
 * to be thrown.  Whether or not a channel is open may be tested by invoking
 * its {@link #isOpen isOpen} method.
 *
 * <p> Channels are, in general, intended to be safe for multithreaded access
 * as described in the specifications of the interfaces and classes that extend
 * and implement this interface.
 *
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */

public interface Channel extends Closeable {

    /**
     * Tells whether or not this channel is open.
     *
     * @return <tt>true</tt> if, and only if, this channel is open
     */
    public boolean isOpen();

    /**
     * Closes this channel.
     *
     * <p> After a channel is closed, any further attempt to invoke I/O
     * operations upon it will cause a {@link ClosedChannelException} to be
     * thrown.
     *
     * <p> If this channel is already closed then invoking this method has no
     * effect.
     *
     * <p> This method may be invoked at any time.  If some other thread has
     * already invoked it, however, then another invocation will block until
     * the first invocation is complete, after which it will return without
     * effect. </p>
     *
     * @throws  IOException  If an I/O error occurs
     */
    public void close() throws IOException;

}

public interface ReadableByteChannel extends Channel {

    /**
     * Reads a sequence of bytes from this channel into the given buffer.
     *
     * <p> An attempt is made to read up to <i>r</i> bytes from the channel,
     * where <i>r</i> is the number of bytes remaining in the buffer, that is,
     * <tt>dst.remaining()</tt>, at the moment this method is invoked.
     *
     * <p> Suppose that a byte sequence of length <i>n</i> is read, where
     * <tt>0</tt>&nbsp;<tt>&lt;=</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&nbsp;<i>r</i>.
     * This byte sequence will be transferred into the buffer so that the first
     * byte in the sequence is at index <i>p</i> and the last byte is at index
     * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>&nbsp;<tt>-</tt>&nbsp;<tt>1</tt>,
     * where <i>p</i> is the buffer's position at the moment this method is
     * invoked.  Upon return the buffer's position will be equal to
     * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>; its limit will not have changed.
     *
     * <p> A read operation might not fill the buffer, and in fact it might not
     * read any bytes at all.  Whether or not it does so depends upon the
     * nature and state of the channel.  A socket channel in non-blocking mode,
     * for example, cannot read any more bytes than are immediately available
     * from the socket's input buffer; similarly, a file channel cannot read
     * any more bytes than remain in the file.  It is guaranteed, however, that
     * if a channel is in blocking mode and there is at least one byte
     * remaining in the buffer then this method will block until at least one
     * byte is read.
     *
     * <p> This method may be invoked at any time.  If another thread has
     * already initiated a read operation upon this channel, however, then an
     * invocation of this method will block until the first operation is
     * complete. </p>
     *
     * @param  dst
     *         The buffer into which bytes are to be transferred
     *
     * @return  The number of bytes read, possibly zero, or <tt>-1</tt> if the
     *          channel has reached end-of-stream
     *
     * @throws  NonReadableChannelException
     *          If this channel was not opened for reading
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  AsynchronousCloseException
     *          If another thread closes this channel
     *          while the read operation is in progress
     *
     * @throws  ClosedByInterruptException
     *          If another thread interrupts the current thread
     *          while the read operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public int read(ByteBuffer dst) throws IOException;

}

public abstract class FileChannel
    extends AbstractInterruptibleChannel
    implements SeekableByteChannel, GatheringByteChannel, ScatteringByteChannel
{
  
}

public class FileChannelImpl extends FileChannel {
     // Memory allocation size for mapping buffers
    private static final long allocationGranularity;

    // Access to FileDescriptor internals
    private static final JavaIOFileDescriptorAccess fdAccess =
        SharedSecrets.getJavaIOFileDescriptorAccess();

    // Used to make native read and write calls
    private final FileDispatcher nd;

    // File descriptor
    private final FileDescriptor fd;

    // File access mode (immutable)
    private final boolean writable;
    private final boolean readable;

    // Required to prevent finalization of creating stream (immutable)
    private final Object parent;

    // The path of the referenced file
    // (null if the parent stream is created with a file descriptor)
    private final String path;

    // Thread-safe set of IDs of native threads, for signalling
    private final NativeThreadSet threads = new NativeThreadSet(2);

    // Lock for operations involving position and size
    private final Object positionLock = new Object();

    // blocking operations are not interruptible
    private volatile boolean uninterruptible;

    // DirectIO flag
    private final boolean direct;

    // IO alignment value for DirectIO
    private final int alignment;

    // Cleanable with an action which closes this channel's file descriptor
    private final Cleanable closer;
  
      // Used by FileInputStream.getChannel(), FileOutputStream.getChannel
    // and RandomAccessFile.getChannel()
    // 从FileInputStream.getChannel(), FileOutputStream.getChannel and RandomAccessFile.getChannel()三种方式获得channel
    public static FileChannel open(FileDescriptor fd, String path,
                                   boolean readable, boolean writable,
                                   boolean direct, Object parent)
    {
        return new FileChannelImpl(fd, path, readable, writable, direct, parent);
    }
  
  
     public int read(ByteBuffer dst, long position) throws IOException {
        if (dst == null)
            throw new NullPointerException();
        if (position < 0)
            throw new IllegalArgumentException("Negative position");
        if (!readable)
            throw new NonReadableChannelException();
        if (direct)
            Util.checkChannelPositionAligned(position, alignment);
        ensureOpen();
        if (nd.needsPositionLock()) {
            synchronized (positionLock) {
                return readInternal(dst, position);
            }
        } else {
            return readInternal(dst, position);
        }
    }

    private int readInternal(ByteBuffer dst, long position) throws IOException {
        assert !nd.needsPositionLock() || Thread.holdsLock(positionLock);
        int n = 0;
        int ti = -1;

        try {
            beginBlocking();
            ti = threads.add();
            if (!isOpen())
                return -1;
            do {
                n = IOUtil.read(fd, dst, position, direct, alignment, nd);
            } while ((n == IOStatus.INTERRUPTED) && isOpen());
            return IOStatus.normalize(n);
        } finally {
            threads.remove(ti);
            endBlocking(n > 0);
            assert IOStatus.check(n);
        }
    }
  
}

public
class FileInputStream extends InputStream
{  
	public FileChannel getChannel() {
        synchronized (this) {
            if (channel == null) {
                channel = FileChannelImpl.open(fd, path, true, false, this);
            }
            return channel;
        }
    }
}

    static int read(FileDescriptor fd, ByteBuffer dst, long position,
                    NativeDispatcher nd)
        throws IOException
    {
        return read(fd, dst, position, false, -1, nd);
    }

    static int read(FileDescriptor fd, ByteBuffer dst, long position,
                    boolean directIO, int alignment, NativeDispatcher nd)
        throws IOException
    {
        if (dst.isReadOnly())
            throw new IllegalArgumentException("Read-only buffer");
        if (dst instanceof DirectBuffer)
            return readIntoNativeBuffer(fd, dst, position, directIO, alignment, nd);

        // Substitute a native buffer
        ByteBuffer bb;
        int rem = dst.remaining();
        if (directIO) {
            Util.checkRemainingBufferSizeAligned(rem, alignment);
            bb = Util.getTemporaryAlignedDirectBuffer(rem, alignment);
        } else {
            bb = Util.getTemporaryDirectBuffer(rem);
        }
        try {
            int n = readIntoNativeBuffer(fd, bb, position, directIO, alignment,nd);
            bb.flip();
            if (n > 0)
                dst.put(bb);
            return n;
        } finally {
            Util.offerFirstTemporaryDirectBuffer(bb);
        }
    }

    private static int readIntoNativeBuffer(FileDescriptor fd, ByteBuffer bb,
                                            long position, boolean directIO,
                                            int alignment, NativeDispatcher nd)
        throws IOException
    {
        int pos = bb.position();
        int lim = bb.limit();
        assert (pos <= lim);
        int rem = (pos <= lim ? lim - pos : 0);

        if (directIO) {
            Util.checkBufferPositionAligned(bb, pos, alignment);
            Util.checkRemainingBufferSizeAligned(rem, alignment);
        }

        if (rem == 0)
            return 0;
        int n = 0;
        if (position != -1) {
            n = nd.pread(fd, ((DirectBuffer)bb).address() + pos, rem, position);
        } else {
            n = nd.read(fd, ((DirectBuffer)bb).address() + pos, rem);
        }
        if (n > 0)
            bb.position(pos + n);
        return n;
    }