java.io
Class BufferedInputStream

java.lang.Object
  java.io.InputStream
      java.io.FilterInputStream
          java.io.BufferedInputStream

public class BufferedInputStream
extends FilterInputStream

This subclass of FilterInputStream buffers input from an underlying implementation to provide a possibly more efficient read mechanism. It maintains the buffer and buffer state in instance variables that are available to subclasses. The default buffer size of 2048 bytes can be overridden by the creator of the stream.

This class also implements mark/reset functionality. It is capable of remembering any number of input bytes, to the limits of system memory or the size of Integer.MAX_VALUE

Please note that this class does not properly handle character encodings. Consider using the BufferedReader class which does.

Field Summary

protected byte[]	buf The buffer used for storing data from the underlying stream.
protected int	count The number of valid bytes currently in the buffer.
protected int	marklimit This is the maximum number of bytes than can be read after a call to mark() before the mark can be discarded.
protected int	markpos The value of pos when the mark() method was called.
protected int	pos The index of the next character that will by read from the buffer.

Fields inherited from class java.io.FilterInputStream

in

Constructor Summary

BufferedInputStream(InputStream in)
This method initializes a new BufferedInputStream that will read from the specified subordinate stream with a default buffer size of 2048 bytes

BufferedInputStream(InputStream in, int size)
This method initializes a new BufferedInputStream that will read from the specified subordinate stream with a buffer size that is specified by the caller.

Method Summary

int	available() This method returns the number of bytes that can be read from this stream before a read can block.
void	close() This method closes the underlying input stream and frees any resources associated with it.
void	mark(int readlimit) This method marks a position in the input to which the stream can be "reset" by calling the reset() method.
boolean	markSupported() This method returns true to indicate that this class supports mark/reset functionality.
int	read() This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255.
int	read(byte[] b, int off, int len) This method reads bytes from a stream and stores them into a caller supplied buffer.
void	reset() This method resets a stream to the point where the mark() method was called.
long	skip(long n) This method skips the specified number of bytes in the stream.

Methods inherited from class java.io.FilterInputStream

read

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

buf

protected byte[] buf

The buffer used for storing data from the underlying stream.

count

protected int count

The number of valid bytes currently in the buffer. It is also the index of the buffer position one byte past the end of the valid data.

pos

protected int pos

The index of the next character that will by read from the buffer. When pos == count, the buffer is empty.

markpos

protected int markpos

The value of pos when the mark() method was called. This is set to -1 if there is no mark set.

marklimit

protected int marklimit

This is the maximum number of bytes than can be read after a call to mark() before the mark can be discarded. After this may bytes are read, the reset() method may not be called successfully.

Constructor Detail

BufferedInputStream

public BufferedInputStream(InputStream in)

This method initializes a new BufferedInputStream that will read from the specified subordinate stream with a default buffer size of 2048 bytes

Parameters:

in - The subordinate stream to read from

BufferedInputStream

public BufferedInputStream(InputStream in,
                           int size)

This method initializes a new BufferedInputStream that will read from the specified subordinate stream with a buffer size that is specified by the caller.

Parameters:

in - The subordinate stream to read from

size - The buffer size to use

Throws:

IllegalArgumentException - when size is smaller then 1

Method Detail

available

public int available()
              throws IOException

This method returns the number of bytes that can be read from this stream before a read can block. A return of 0 indicates that blocking might (or might not) occur on the very next read attempt.

The number of available bytes will be the number of read ahead bytes stored in the internal buffer plus the number of available bytes in the underlying stream.

Overrides:

available in class FilterInputStream

Returns:

The number of bytes that can be read before blocking could occur

Throws:

IOException - If an error occurs

close

public void close()
           throws IOException

This method closes the underlying input stream and frees any resources associated with it. Sets buf to null.

Overrides:

close in class FilterInputStream

Throws:

IOException - If an error occurs.

mark

public void mark(int readlimit)

This method 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 bytes 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 bytes 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.

Note that the number of bytes that can be remembered by this method can be greater than the size of the internal read buffer. It is also not dependent on the subordinate stream supporting mark/reset functionality.

Overrides:

mark in class FilterInputStream

Parameters:

readlimit - The number of bytes that can be read before the mark becomes invalid

markSupported

public boolean markSupported()

This method returns true to indicate that this class supports mark/reset functionality.

Overrides:

markSupported in class FilterInputStream

Returns:

true to indicate that mark/reset functionality is supported

read

public int read()
         throws IOException

This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255. This method also will return -1 if the end of the stream has been reached.

This method will block until the byte can be read.

Overrides:

read in class FilterInputStream

Returns:

The byte read or -1 if end of stream

Throws:

IOException - If an error occurs

read

public int read(byte[] b,
                int off,
                int len)
         throws IOException

This method reads bytes from a stream and stores them into a caller supplied buffer. It starts storing the data at index off into the buffer and attempts to read len bytes. This method can return before reading the number of bytes requested, but it will try to read the requested number of bytes by repeatedly calling the underlying stream as long as available() for this stream continues to return a non-zero value (or until the requested number of bytes have been read). The actual number of bytes 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.

Overrides:

read in class FilterInputStream

Parameters:

b - The array into which the bytes read should be stored

off - The offset into the array to start storing bytes

len - The requested number of bytes to read

Returns:

The actual number of bytes read, or -1 if end of stream.

Throws:

IOException - If an error occurs.

IndexOutOfBoundsException - when off or len are negative, or when off + len is larger then the size of b,

reset

public void reset()
           throws IOException

This method resets a stream to the point where the mark() method was called. Any bytes that were read after the mark point was set will be re-read during subsequent reads.

This method will throw an IOException if the number of bytes read from the stream since the call to mark() exceeds the mark limit passed when establishing the mark.

Overrides:

reset in class FilterInputStream

Throws:

IOException - If mark() was never called or more then marklimit bytes were read since the last call to mark()

skip

public long skip(long n)
          throws IOException

This method skips the specified number of bytes in the stream. It returns the actual number of bytes skipped, which may be less than the requested amount.

Overrides:

skip in class FilterInputStream

Parameters:

n - The requested number of bytes to skip

Returns:

The actual number of bytes skipped.

Throws:

IOException - If an error occurs