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 1.0
*/
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 b.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.
* @throws IOException if {@code in.skip(n)} throws an IOException.
*/
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();
}
}