Object used for synchronizing critical code
* sections. Subclasses should use this variable instead of a
* synchronized method or an explicit synchronization on this
*/
protected Object lock;
/**
* Unitializes a Reader that will use the object
* itself for synchronization of critical code sections.
*/
protected Reader()
{
this.lock = this;
}
/**
* Initializes a Reader that will use the specified
* Object for synchronization of critical code sections.
*
* @param lock The Object to use for synchronization
*/
protected Reader(Object lock)
{
this.lock = lock;
}
/**
* Read chars from a stream and stores them into a caller
* supplied buffer. It starts storing the data at index offset
* into the buffer and attempts to read len chars. This method
* can return before reading the number of chars requested. The actual
* number of chars read is returned as an int. A -1 is returned to indicate
* the end of the stream.
* * This method will block until some data can be read. *
* This method operates by calling the single char read() method
* in a loop until the desired number of chars are read. The read loop
* stops short if the end of the stream is encountered or if an IOException
* is encountered on any read operation except the first. If the first
* attempt to read a chars fails, the IOException is allowed to propagate
* upward. And subsequent IOException is caught and treated identically
* to an end of stream condition. Subclasses can (and should if possible)
* override this method to provide a more efficient implementation.
*
* @param buf The array into which the chars read should be stored
* @param offset The offset into the array to start storing chars
* @param count The requested number of chars to read
*
* @return The actual number of chars read, or -1 if end of stream.
*
* @exception IOException If an error occurs.
*/
public abstract int read(char buf[], int offset, int count)
throws IOException;
/**
* Reads chars from a stream and stores them into a caller
* supplied buffer. This method attempts to completely fill the buffer,
* but can return before doing so. The actual number of chars read is
* returned as an int. A -1 is returned to indicate the end of the stream.
*
* This method will block until some data can be read. *
* This method operates by calling an overloaded read method like so:
* read(buf, 0, buf.length)
*
* @param buf The buffer into which the chars read will be stored.
*
* @return The number of chars read or -1 if end of stream.
*
* @exception IOException If an error occurs.
*/
public int read(char buf[]) throws IOException
{
return read(buf, 0, buf.length);
}
/**
* Reads an char from the input stream and returns it
* as an int in the range of 0-65535. This method also will return -1 if
* the end of the stream has been reached.
*
* This method will block until the char can be read.
*
* @return The char read or -1 if end of stream
*
* @exception IOException If an error occurs
*/
public int read() throws IOException
{
char[] buf = new char[1];
int count = read(buf, 0, 1);
return count > 0 ? buf[0] : -1;
}
/**
* Closes the stream. Any futher attempts to read from the
* stream may generate an IOException.
*
* @exception IOException If an error occurs
*/
public abstract void close() throws IOException;
/**
* Returns a boolean that indicates whether the mark/reset
* methods are supported in this class. Those methods can be used to
* remember a specific point in the stream and reset the stream to that
* point.
*
* This method always returns false in this class, but
* subclasses can override this method to return true if they
* support mark/reset functionality.
*
* @return true if mark/reset functionality is supported,
* false otherwise
*
*/
public boolean markSupported()
{
return false;
}
/**
* Marks a position in the input to which the stream can be
* "reset" by calling the reset() method. The parameter
* readlimit is the number of chars that can be read from the
* stream after setting the mark before the mark becomes invalid. For
* example, if mark() is called with a read limit of 10, then
* when 11 chars of data are read from the stream before the
* reset() method is called, then the mark is invalid and the
* stream object instance is not required to remember the mark.
*
* @param readLimit The number of chars that can be read before the mark
* becomes invalid
*
* @exception IOException If an error occurs such as mark not being
* supported for this class
*/
public void mark(int readLimit) throws IOException
{
throw new IOException("mark not supported");
}
/**
* Resets a stream to the point where the mark()
* method was called. Any chars that were read after the mark point was
* set will be re-read during subsequent reads.
*
* This method always throws an IOException in this class, but subclasses
* can override this method if they provide mark/reset functionality.
*
* @exception IOException Always thrown for this class
*/
public void reset() throws IOException
{
throw new IOException("reset not supported");
}
/**
* Determines whether or not this stream is ready to be
* read. If it returns false the stream may block if a
* read is attempted, but it is not guaranteed to do so.
*
* This method always returns false in this class
*
* @return true if the stream is ready to be read,
* false otherwise.
*
* @exception IOException If an error occurs
*/
public boolean ready() throws IOException
{
return false;
}
/**
* Skips the specified number of chars in the stream. It
* returns the actual number of chars skipped, which may be less than the
* requested amount.
*
* This method reads and discards chars into a 256 char array until the * specified number of chars were skipped or until either the end of stream * is reached or a read attempt returns a short count. Subclasses can * override this method to provide a more efficient implementation where * one exists. * * @param count The requested number of chars to skip * * @return The actual number of chars skipped. * * @exception IOException If an error occurs */ public long skip(long count) throws IOException { if (count <= 0) return 0; int bsize = count > 1024 ? 1024 : (int) count; char[] buffer = new char[bsize]; long todo = count; synchronized (lock) { while (todo > 0) { int skipped = read(buffer, 0, bsize > todo ? (int) todo : bsize); if (skipped <= 0) break; todo -= skipped; } } return count - todo; } }