File	Doc	Category	Size	Date	Package
BufferedInputStream.java	API Doc	Java SE 5 API	15862	Fri Aug 26 14:56:58 BST 2005	java.io

BufferedInputStream

• java.lang.Object
  • java.io.InputStream
    • java.io.FilterInputStream

Fields Summary
private static int	defaultBufferSize
protected volatile byte[]	buf The internal buffer array where the data is stored. When necessary, it may be replaced by another array of a different size.
private static final AtomicReferenceFieldUpdater	bufUpdater Atomic updater to provide compareAndSet for buf. This is necessary because closes can be asynchronous. We use nullness of buf[] as primary indicator that this stream is closed. (The "in" field is also nulled out on close.)
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 int	available() 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 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 return getInIfOpen().available() + (count - pos);
public void	close() Closes this input stream and releases any system resources associated with the stream. exception IOException if an I/O error occurs. byte[] buffer; while ( (buffer = buf) != null) { if (bufUpdater.compareAndSet(this, buffer, null)) { InputStream input = in; in = null; if (input != null) input.close(); return; } // Else retry in case a new buf was CASed in fill() }
private void	fill() Fills the buffer with more data, taking into account shuffling and other tricks for 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. byte[] buffer = getBufIfOpen(); if (markpos < 0) pos = 0; /* no mark: throw away the buffer */ else if (pos >= buffer.length) /* no room left in buffer */ if (markpos > 0) { /* can throw away early part of the buffer */ int sz = pos - markpos; System.arraycopy(buffer, markpos, buffer, 0, sz); pos = sz; markpos = 0; } else if (buffer.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(buffer, 0, nbuf, 0, pos); if (!bufUpdater.compareAndSet(this, buffer, nbuf)) { // Can't replace buf if there was an async close. // Note: This would need to be changed if fill() // is ever made accessible to multiple threads. // But for now, the only way CAS can fail is via close. // assert buf == null; throw new IOException("Stream closed"); } buffer = nbuf; } count = pos; int n = getInIfOpen().read(buffer, pos, buffer.length - pos); if (n > 0) count = n + pos;
private byte[]	getBufIfOpen() Check to make sure that buffer has not been nulled out due to close; if not return it; byte[] buffer = buf; if (buffer == null) throw new IOException("Stream closed"); return buffer;
private java.io.InputStream	getInIfOpen() Check to make sure that underlying input stream has not been nulled out due to close; if not return it; InputStream input = in; if (input == null) throw new IOException("Stream closed"); return input;
public synchronized void	mark(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 boolean	markSupported() 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 int	read() 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) { fill(); if (pos >= count) return -1; } return getBufIfOpen()[pos++] & 0xff;
public synchronized int	read(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. getBufIfOpen(); // Check for closed stream if ((off | len | (off + len) | (b.length - (off + len))) < 0) { throw new IndexOutOfBoundsException(); } else if (len == 0) { return 0; } int n = 0; for (;;) { int nread = read1(b, off + n, len - n); if (nread <= 0) return (n == 0) ? nread : n; n += nread; if (n >= len) return n; // if not closed but no bytes available, return InputStream input = in; if (input != null && input.available() <= 0) return n; }
private int	read1(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 >= getBufIfOpen().length && markpos < 0) { return getInIfOpen().read(b, off, len); } fill(); avail = count - pos; if (avail <= 0) return -1; } int cnt = (avail < len) ? avail : len; System.arraycopy(getBufIfOpen(), pos, b, off, cnt); pos += cnt; return cnt;
public synchronized void	reset() 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) getBufIfOpen(); // Cause exception if closed if (markpos < 0) throw new IOException("Resetting to invalid mark"); pos = markpos;
public synchronized long	skip(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. getBufIfOpen(); // Check for closed stream 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 getInIfOpen().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;