/*
 * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 */

package java.io;

/**
 * A <code>FilterInputStream</code> contains
 * some other input stream, which it uses as
 * its  basic source of data, possibly transforming
 * the data along the way or providing  additional
 * functionality. The class <code>FilterInputStream</code>
 * itself simply overrides all  methods of
 * <code>InputStream</code> with versions that
 * pass all requests to the contained  input
 * stream. Subclasses of <code>FilterInputStream</code>
 * may further override some of  these methods
 * and may also provide additional methods
 * and fields.
 *
 * @author  Jonathan Payne
 * @since   JDK1.0
 */
//持有其他inputstream并进行一定的处理，典型的装饰器模式还是代理模式？
public
class FilterInputStream extends InputStream {
    //持有一个inputstream
    protected volatile InputStream in;

    
    protected FilterInputStream(InputStream in) {
        this.in = in;
    }

    
    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);
    }

    /**
     * Skips over and discards <code>n</code> bytes of data from the
     * input stream. The <code>skip</code> method may, for a variety of
     * reasons, end up skipping over some smaller number of bytes,
     * possibly <code>0</code>. The actual number of bytes skipped is
     * returned.
     * <p>
     * This method simply performs <code>in.skip(n)</code>.
     *
     * @param      n   the number of bytes to be skipped.
     * @return     the actual number of bytes skipped.
     * @exception  IOException  if the stream does not support seek,
     *                          or if some other I/O error occurs.
     */
    public long skip(long n) throws IOException {
        return in.skip(n);
    }

    /**
     * Returns an estimate of the number of bytes that can be read (or
     * skipped over) from this input stream without blocking by the next
     * caller of a method for this input stream. The next caller might be
     * the same thread or another thread.  A single read or skip of this
     * many bytes will not block, but may read or skip fewer bytes.
     * <p>
     * This method returns the result of {@link #in in}.available().
     *
     * @return     an estimate of the number of bytes that can be read (or skipped
     *             over) from this input stream without blocking.
     * @exception  IOException  if an I/O error occurs.
     */
    public int available() throws IOException {
        return in.available();
    }

    /**
     * Closes this input stream and releases any system resources
     * associated with the stream.
     * This
     * method simply performs <code>in.close()</code>.
     *
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public void close() throws IOException {
        in.close();
    }

    /**
     * Marks the current position in this input stream. A subsequent
     * call to the <code>reset</code> method repositions this stream at
     * the last marked position so that subsequent reads re-read the same bytes.
     * <p>
     * The <code>readlimit</code> argument tells this input stream to
     * allow that many bytes to be read before the mark position gets
     * invalidated.
     * <p>
     * This method simply performs <code>in.mark(readlimit)</code>.
     *
     * @param   readlimit   the maximum limit of bytes that can be read before
     *                      the mark position becomes invalid.
     * @see     java.io.FilterInputStream#in
     * @see     java.io.FilterInputStream#reset()
     */
    public synchronized void mark(int readlimit) {
        in.mark(readlimit);
    }

    /**
     * Repositions this stream to the position at the time the
     * <code>mark</code> method was last called on this input stream.
     * <p>
     * This method
     * simply performs <code>in.reset()</code>.
     * <p>
     * Stream marks are intended to be used in
     * situations where you need to read ahead a little to see what's in
     * the stream. Often this is most easily done by invoking some
     * general parser. If the stream is of the type handled by the
     * parse, it just chugs along happily. If the stream is not of
     * that type, the parser should toss an exception when it fails.
     * If this happens within readlimit bytes, it allows the outer
     * code to reset the stream and try another parser.
     *
     * @exception  IOException  if the stream has not been marked or if the
     *               mark has been invalidated.
     * @see        java.io.FilterInputStream#in
     * @see        java.io.FilterInputStream#mark(int)
     */
    public synchronized void reset() throws IOException {
        in.reset();
    }

    /**
     * Tests if this input stream supports the <code>mark</code>
     * and <code>reset</code> methods.
     * This method
     * simply performs <code>in.markSupported()</code>.
     *
     * @return  <code>true</code> if this stream type supports the
     *          <code>mark</code> and <code>reset</code> method;
     *          <code>false</code> otherwise.
     * @see     java.io.FilterInputStream#in
     * @see     java.io.InputStream#mark(int)
     * @see     java.io.InputStream#reset()
     */
    public boolean markSupported() {
        return in.markSupported();
    }
}