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
* @since JDK1.0
*/
public class BufferedInputStream extends FilterInputStream {
private static int DEFAULT_BUFFER_SIZE = 8192;
/**
* The maximum size of array to allocate. Some VMs reserve some header words in an array. Attempts to allocate
* larger arrays may result in OutOfMemoryError: Requested array size exceeds VM limit
*/
private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
/**
* The internal buffer array where the data is stored. When necessary, it may be replaced by another array of a
* different size.
*/
@Nullable
protected volatile byte buf[];
/**
* 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 count;
/**
* 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.
*
* @see java.io.BufferedInputStream#buf
*/
protected int pos;
/**
* 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.
*
* @see java.io.BufferedInputStream#mark(int)
* @see java.io.BufferedInputStream#pos
*/
protected int markpos = -1;
/**
* 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.
*
* @see java.io.BufferedInputStream#mark(int)
* @see java.io.BufferedInputStream#reset()
*/
protected int marklimit;
/**
* Check to make sure that underlying input stream has not been nulled out due to close; if not return it;
*/
private InputStream getInIfOpen() throws IOException {
InputStream input = this.in;
if (input == null) {
throw new IOException("Stream closed");
}
return input;
}
/**
* Check to make sure that buffer has not been nulled out due to close; if not return it;
*/
private byte[] getBufIfOpen() throws IOException {
byte[] buffer = this.buf;
if (buffer == null) {
throw new IOException("Stream closed");
}
return buffer;
}
/**
* 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.
*/
public BufferedInputStream(InputStream in) {
this(in, DEFAULT_BUFFER_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 {@code size <= 0}.
*/
public BufferedInputStream(InputStream in, int size) {
super(in);
if (size <= 0) {
throw new IllegalArgumentException("Buffer size <= 0");
}
this.buf = new byte[size];
}
/**
* 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.
*/
private void fill() throws IOException {
byte[] buffer = getBufIfOpen();
if (this.markpos < 0) {
this.pos = 0; /* no mark: throw away the buffer */
} else if (this.pos >= buffer.length) {
if (this.markpos > 0) { /* can throw away early part of the buffer */
int sz = this.pos - this.markpos;
System.arraycopy(buffer, this.markpos, buffer, 0, sz);
this.pos = sz;
this.markpos = 0;
} else if (buffer.length >= this.marklimit) {
this.markpos = -1; /* buffer got too big, invalidate mark */
this.pos = 0; /* drop buffer contents */
} else if (buffer.length >= MAX_BUFFER_SIZE) {
throw new OutOfMemoryError("Required array size too large");
} else { /* grow buffer */
int nsz = (this.pos <= MAX_BUFFER_SIZE - this.pos) ? this.pos * 2 : MAX_BUFFER_SIZE;
if (nsz > this.marklimit) {
nsz = this.marklimit;
}
byte nbuf[] = new byte[nsz];
System.arraycopy(buffer, 0, nbuf, 0, this.pos);
this.buf = nbuf;
buffer = nbuf;
}
}
this.count = this.pos;
int n = getInIfOpen().read(buffer, this.pos, buffer.length - this.pos);
if (n > 0) {
this.count = n + this.pos;
}
}
/**
* 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 this input stream has been closed by invoking its {@link #close()} method, or an I/O error
* occurs.
* @see java.io.FilterInputStream#in
*/
@Override
public synchronized int read() throws IOException {
if (this.pos >= this.count) {
fill();
if (this.pos >= this.count) {
return -1;
}
}
return getBufIfOpen()[this.pos++] & 0xff;
}
/**
* Read characters into a portion of an array, reading from the underlying stream at most once if necessary.
*/
private int read1(byte[] b, int off, int len) throws IOException {
int avail = this.count - this.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 && this.markpos < 0) {
return getInIfOpen().read(b, off, len);
}
fill();
avail = this.count - this.pos;
if (avail <= 0) {
return -1;
}
}
int cnt = (avail < len) ? avail : len;
System.arraycopy(getBufIfOpen(), this.pos, b, off, cnt);
this.pos += cnt;
return cnt;
}
/**
* 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:
*
read method of the underlying stream returns -1, indicating end-of-file, or
*
* available method of the underlying stream returns zero, indicating that further input
* requests would block.
*
* 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 this input stream has been closed by invoking its {@link #close()} method, or an I/O error
* occurs.
*/
@Override
public synchronized int read(byte b[], int off, int len) throws IOException {
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 = this.in;
if (input != null && input.available() <= 0) {
return n;
}
}
}
/**
* See the general contract of the skip method of InputStream.
*
* @exception IOException
* if the stream does not support seek, or if this input stream has been closed by invoking its
* {@link #close()} method, or an I/O error occurs.
*/
@Override
public synchronized long skip(long n) throws IOException {
getBufIfOpen(); // Check for closed stream
if (n <= 0) {
return 0;
}
long avail = this.count - this.pos;
if (avail <= 0) {
// If no mark position set then don't keep in buffer
if (this.markpos < 0) {
return getInIfOpen().skip(n);
}
// Fill in buffer to save bytes for reset
fill();
avail = this.count - this.pos;
if (avail <= 0) {
return 0;
}
}
long skipped = (avail < n) ? avail : n;
this.pos += skipped;
return skipped;
}
/**
* Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without
* blocking by the next invocation of a method for this input stream. The next invocation 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 sum of the number of bytes remaining to be read in the buffer
* (count - pos) and the result of calling the {@link java.io.FilterInputStream#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 this input stream has been closed by invoking its {@link #close()} method, or an I/O error
* occurs.
*/
@Override
public synchronized int available() throws IOException {
int n = this.count - this.pos;
int avail = getInIfOpen().available();
return n > (Integer.MAX_VALUE - avail) ? Integer.MAX_VALUE : n + avail;
}
/**
* 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()
*/
@Override
public synchronized void mark(int readlimit) {
this.marklimit = readlimit;
this.markpos = this.pos;
}
/**
* 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, or the stream has been
* closed by invoking its {@link #close()} method, or an I/O error occurs.
* @see java.io.BufferedInputStream#mark(int)
*/
@Override
public synchronized void reset() throws IOException {
getBufIfOpen(); // Cause exception if closed
if (this.markpos < 0) {
throw new IOException("Resetting to invalid mark");
}
this.pos = this.markpos;
}
/**
* 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()
*/
@Override
public boolean markSupported() {
return true;
}
/**
* Closes this input stream and releases any system resources associated with the stream. Once the stream has been
* closed, further read(), available(), reset(), or skip() invocations will throw an IOException. Closing a
* previously closed stream has no effect.
*
* @exception IOException
* if an I/O error occurs.
*/
@Override
@SuppressWarnings("null")
public void close() throws IOException {
this.buf = null;
InputStream input = this.in;
this.in = null;
if (input != null) {
input.close();
}
}
}