FilterInputStream 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 FilterInputStream
+ * itself simply overrides all methods of
+ * InputStream with versions that
+ * pass all requests to the contained input
+ * stream. Subclasses of FilterInputStream
+ * may further override some of these methods
+ * and may also provide additional methods
+ * and fields.
+ *
+ * @author Jonathan Payne
+ * @since JDK1.0
+ */
+public
+class FilterInputStream extends InputStream {
+ /**
+ * The input stream to be filtered.
+ */
+ protected volatile InputStream in;
+
+ /**
+ * Creates a FilterInputStream
+ * by assigning the argument in
+ * to the field this.in so as
+ * to remember it for later use.
+ *
+ * @param in the underlying input stream, or null if
+ * this instance is to be created without an underlying stream.
+ */
+ protected FilterInputStream(InputStream in) {
+ this.in = in;
+ }
+
+ /**
+ * Reads the next byte of data from this input stream. The value
+ * byte is returned as an int in the range
+ * 0 to 255. If no byte is available
+ * because the end of the stream has been reached, the value
+ * -1 is returned. This method blocks until input data
+ * is available, the end of the stream is detected, or an exception
+ * is thrown.
+ *
+ * This method
+ * simply performs in.read() and returns the result.
+ *
+ * @return the next byte of data, or -1 if the end of the
+ * stream is reached.
+ * @exception IOException if an I/O error occurs.
+ * @see java.io.FilterInputStream#in
+ */
+ public int read() throws IOException {
+ return in.read();
+ }
+
+ /**
+ * Reads up to byte.length bytes of data from this
+ * input stream into an array of bytes. This method blocks until some
+ * input is available.
+ *
+ * This method simply performs the call
+ * read(b, 0, b.length) and returns
+ * the result. It is important that it does
+ * not do in.read(b) instead;
+ * certain subclasses of FilterInputStream
+ * depend on the implementation strategy actually
+ * used.
+ *
+ * @param b the buffer into which the data is read.
+ * @return the total number of bytes read into the buffer, or
+ * -1 if there is no more data because the end of
+ * the stream has been reached.
+ * @exception IOException if an I/O error occurs.
+ * @see java.io.FilterInputStream#read(byte[], int, int)
+ */
+ public int read(byte b[]) throws IOException {
+ return read(b, 0, b.length);
+ }
+
+ /**
+ * Reads up to len bytes of data from this input stream
+ * into an array of bytes. If len is not zero, the method
+ * blocks until some input is available; otherwise, no
+ * bytes are read and 0 is returned.
+ *
+ * This method simply performs in.read(b, off, len)
+ * and returns the result.
+ *
+ * @param b the buffer into which the data is read.
+ * @param off the start offset in the destination array b
+ * @param len the maximum number of bytes read.
+ * @return the total number of bytes read into the buffer, or
+ * -1 if there is no more data because the end of
+ * the stream has been reached.
+ * @exception NullPointerException If b is null.
+ * @exception IndexOutOfBoundsException If off is negative,
+ * len is negative, or len is greater than
+ * b.length - off
+ * @exception IOException if an I/O error occurs.
+ * @see java.io.FilterInputStream#in
+ */
+ public int read(byte b[], int off, int len) throws IOException {
+ return in.read(b, off, len);
+ }
+
+ /**
+ * Skips over and discards n bytes of data from the
+ * input stream. The skip method may, for a variety of
+ * reasons, end up skipping over some smaller number of bytes,
+ * possibly 0. The actual number of bytes skipped is
+ * returned.
+ *
+ * This method simply performs in.skip(n).
+ *
+ * @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.
+ *
+ * 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 in.close().
+ *
+ * @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 reset method repositions this stream at
+ * the last marked position so that subsequent reads re-read the same bytes.
+ *
+ * The readlimit argument tells this input stream to
+ * allow that many bytes to be read before the mark position gets
+ * invalidated.
+ *
+ * This method simply performs in.mark(readlimit).
+ *
+ * @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
+ * mark method was last called on this input stream.
+ *
+ * This method
+ * simply performs in.reset().
+ *
+ * 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 mark
+ * and reset methods.
+ * This method
+ * simply performs in.markSupported().
+ *
+ * @return true if this stream type supports the
+ * mark and reset method;
+ * false otherwise.
+ * @see java.io.FilterInputStream#in
+ * @see java.io.InputStream#mark(int)
+ * @see java.io.InputStream#reset()
+ */
+ public boolean markSupported() {
+ return in.markSupported();
+ }
+}