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BufferedInputStream.javaAPI DocphoneME MR2 API (J2ME)14645Wed May 02 18:00:34 BST 2007com.sun.perseus.platform

BufferedInputStream

public class BufferedInputStream extends FilterInputStream
A BufferedInputStream adds functionality to another input stream-namely, the ability to buffer the input and to support the mark and reset methods. When the BufferedInputStream is created, an internal buffer array is created. As bytes from the stream are read or skipped, the internal buffer is refilled as necessary from the contained input stream, many bytes at a time. The mark operation remembers a point in the input stream and the reset operation causes all the bytes read since the most recent mark operation to be reread before new bytes are taken from the contained input stream.
author
Arthur van Hoff
version
1.44 11/09/00
since
JDK1.0

Fields Summary
private static int
defaultBufferSize
protected byte[]
buf
The internal buffer array where the data is stored. When necessary, it may be replaced by another array of a different size.
protected int
count
The index one greater than the index of the last valid byte in the buffer. This value is always in the range 0 through buf.length; elements buf[0] through buf[count-1] contain buffered input data obtained from the underlying input stream.
protected int
pos
The current position in the buffer. This is the index of the next character to be read from the buf array.

This value is always in the range 0 through count. If it is less than count, then buf[pos] is the next byte to be supplied as input; if it is equal to count, then the next read or skip operation will require more bytes to be read from the contained input stream.

protected int
markpos
The value of the pos field at the time the last mark method was called.

This value is always in the range -1 through pos. If there is no marked position in the input stream, this field is -1. If there is a marked position in the input stream, then buf[markpos] is the first byte to be supplied as input after a reset operation. If markpos is not -1, then all bytes from positions buf[markpos] through buf[pos-1] must remain in the buffer array (though they may be moved to another place in the buffer array, with suitable adjustments to the values of count, pos, and markpos); they may not be discarded unless and until the difference between pos and markpos exceeds marklimit.

protected int
marklimit
The maximum read ahead allowed after a call to the mark method before subsequent calls to the reset method fail. Whenever the difference between pos and markpos exceeds marklimit, then the mark may be dropped by setting markpos to -1.
Constructors Summary
public BufferedInputStream(InputStream in)
Creates a BufferedInputStream and saves its argument, the input stream in, for later use. An internal buffer array is created and stored in buf.

param
in the underlying input stream.

	this(in, defaultBufferSize);
    
public BufferedInputStream(InputStream in, int size)
Creates a BufferedInputStream with the specified buffer size, and saves its argument, the input stream in, for later use. An internal buffer array of length size is created and stored in buf.

param
in the underlying input stream.
param
size the buffer size.
exception
IllegalArgumentException if size <= 0.

	super(in);
        if (size <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
	buf = new byte[size];
    
Methods Summary
public synchronized intavailable()
Returns the number of bytes that can be read from this input stream without blocking.

The available method of BufferedInputStream returns the sum of the the number of bytes remaining to be read in the buffer (count - pos) and the result of calling the available method of the underlying input stream.

return
the number of bytes that can be read from this input stream without blocking.
exception
IOException if an I/O error occurs.
see
java.io.FilterInputStream#in

        ensureOpen();
	return (count - pos) + in.available();
    
public voidclose()
Closes this input stream and releases any system resources associated with the stream.

exception
IOException if an I/O error occurs.

        if (in == null)
            return;
        in.close();
        in = null;
        buf = null;
	pos = count = 0;
    
private voidensureOpen()
Check to make sure that this stream has not been closed


                    
         
	if (in == null)
	    throw new IOException("Stream closed");
    
private voidfill()
Fills the buffer with more data, taking into account shuffling and dealing with marks. Assumes that it is being called by a synchronized method. This method also assumes that all data has already been read in, hence pos > count.

	if (markpos < 0)
	    pos = 0;		/* no mark: throw away the buffer */
	else if (pos >= buf.length)	/* no room left in buffer */
	    if (markpos > 0) {	/* can throw away early part of the buffer */
		int sz = pos - markpos;
		System.arraycopy(buf, markpos, buf, 0, sz);
		pos = sz;
		markpos = 0;
	    } else if (buf.length >= marklimit) {
		markpos = -1;	/* buffer got too big, invalidate mark */
		pos = 0;	/* drop buffer contents */
	    } else {		/* grow buffer */
		int nsz = pos * 2;
		if (nsz > marklimit)
		    nsz = marklimit;
		byte nbuf[] = new byte[nsz];
		System.arraycopy(buf, 0, nbuf, 0, pos);
		buf = nbuf;
	    }
        count = pos;
	int n = in.read(buf, pos, buf.length - pos);
        if (n > 0)
            count = n + pos;
    
public synchronized voidmark(int readlimit)
See the general contract of the mark method of InputStream.

param
readlimit the maximum limit of bytes that can be read before the mark position becomes invalid.
see
java.io.BufferedInputStream#reset()

	marklimit = readlimit;
	markpos = pos;
    
public booleanmarkSupported()
Tests if this input stream supports the mark and reset methods. The markSupported method of BufferedInputStream returns true.

return
a boolean indicating if this stream type supports the mark and reset methods.
see
java.io.InputStream#mark(int)
see
java.io.InputStream#reset()

	return true;
    
public synchronized intread()
See the general contract of the read method of InputStream.

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

	if (pos >= count) {
	    ensureOpen();
	    fill();
	    if (pos >= count)
		return -1;
	}
	return buf[pos++] & 0xff;
    
public synchronized intread(byte[] b, int off, int len)
Reads bytes from this byte-input stream into the specified byte array, starting at the given offset.

This method implements the general contract of the corresponding {@link InputStream#read(byte[], int, int) read} method of the {@link InputStream} class. As an additional convenience, it attempts to read as many bytes as possible by repeatedly invoking the read method of the underlying stream. This iterated read continues until one of the following conditions becomes true:

  • The specified number of bytes have been read,
  • The read method of the underlying stream returns -1, indicating end-of-file, or
  • The available method of the underlying stream returns zero, indicating that further input requests would block.
If the first read on the underlying stream returns -1 to indicate end-of-file then this method returns -1. Otherwise this method returns the number of bytes actually read.

Subclasses of this class are encouraged, but not required, to attempt to read as many bytes as possible in the same fashion.

param
b destination buffer.
param
off offset at which to start storing bytes.
param
len maximum number of bytes to read.
return
the number of bytes read, or -1 if the end of the stream has been reached.
exception
IOException if an I/O error occurs.

        ensureOpen();
        if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
	    throw new IndexOutOfBoundsException();
	} else if (len == 0) {
	    return 0;
	}

	int n = read1(b, off, len);
	if (n <= 0) return n;
	while ((n < len) && (in.available() > 0)) {
	    int n1 = read1(b, off + n, len - n);
	    if (n1 <= 0) break;
	    n += n1;
	}
	return n;
    
private intread1(byte[] b, int off, int len)
Read characters into a portion of an array, reading from the underlying stream at most once if necessary.

	int avail = count - pos;
	if (avail <= 0) {
	    /* If the requested length is at least as large as the buffer, and
	       if there is no mark/reset activity, do not bother to copy the
	       bytes into the local buffer.  In this way buffered streams will
	       cascade harmlessly. */
	    if (len >= buf.length && markpos < 0) {
		return in.read(b, off, len);
	    }
	    fill();
	    avail = count - pos;
	    if (avail <= 0) return -1;
	}
	int cnt = (avail < len) ? avail : len;
	System.arraycopy(buf, pos, b, off, cnt);
	pos += cnt;
	return cnt;
    
public synchronized voidreset()
See the general contract of the reset method of InputStream.

If markpos is -1 (no mark has been set or the mark has been invalidated), an IOException is thrown. Otherwise, pos is set equal to markpos.

exception
IOException if this stream has not been marked or if the mark has been invalidated.
see
java.io.BufferedInputStream#mark(int)

        ensureOpen();
	if (markpos < 0)
	    throw new IOException("Resetting to invalid mark");
	pos = markpos;
    
public synchronized longskip(long n)
See the general contract of the skip method of InputStream.

param
n the number of bytes to be skipped.
return
the actual number of bytes skipped.
exception
IOException if an I/O error occurs.

        ensureOpen();
	if (n <= 0) {
	    return 0;
	}
	long avail = count - pos;
     
        if (avail <= 0) {
            // If no mark position set then don't keep in buffer
            if (markpos <0) 
                return in.skip(n);
            
            // Fill in buffer to save bytes for reset
            fill();
            avail = count - pos;
            if (avail <= 0)
                return 0;
        }
        
        long skipped = (avail < n) ? avail : n;
        pos += skipped;
        return skipped;