Applications that need to define a subclass of InputStream
* must always provide a method that returns the next byte of input.
*
* @author Arthur van Hoff
* @version 1.36, 02/02/00
* @see java.io.BufferedInputStream
* @see java.io.ByteArrayInputStream
* @see java.io.DataInputStream
* @see java.io.FilterInputStream
* @see java.io.InputStream#read()
* @see java.io.OutputStream
* @see java.io.PushbackInputStream
* @since JDK1.0
*/
public abstract class InputStream {
// SKIP_BUFFER_SIZE is used to determine the size of skipBuffer
// private static final int SKIP_BUFFER_SIZE = 2048;
private static final int SKIP_BUFFER_SIZE = 32;
// skipBuffer is initialized in skip(long), if needed.
private static byte[] skipBuffer;
/**
* Reads the next byte of data from the input stream. The value byte is
* returned as an int in the range 0 to
* 255. If no byte is available because the end of the stream
* has been reached, the value -1 is returned. This method
* blocks until input data is available, the end of the stream is detected,
* or an exception is thrown.
*
*
A subclass must provide an implementation of this method.
*
* @return the next byte of data, or -1 if the end of the
* stream is reached.
* @exception IOException if an I/O error occurs.
*/
public abstract int read() throws IOException;
/**
* Reads some number of bytes from the input stream and stores them into
* the buffer array b. The number of bytes actually read is
* returned as an integer. This method blocks until input data is
* available, end of file is detected, or an exception is thrown.
*
*
If b is null, a
* NullPointerException is thrown. If the length of
* b is zero, then no bytes are read and 0 is
* returned; otherwise, there is an attempt to read at least one byte. If
* no byte is available because the stream is at end of file, the value
* -1 is returned; otherwise, at least one byte is read and
* stored into b.
*
*
The first byte read is stored into element b[0], the
* next one into b[1], and so on. The number of bytes read is,
* at most, equal to the length of b. Let k be the
* number of bytes actually read; these bytes will be stored in elements
* b[0] through b[k-1],
* leaving elements b[k] through
* b[b.length-1] unaffected.
*
*
If the first byte cannot be read for any reason other than end of
* file, then an IOException is thrown. In particular, an
* IOException is thrown if the input stream has been closed.
*
*
The read(b) method for class InputStream
* has the same effect as:
read(b, 0, b.length) -1 is there is no more data because the end of
* the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.InputStream#read(byte[], int, int)
*/
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
/**
* Reads up to len bytes of data from the input stream into
* an array of bytes. An attempt is made to read as many as
* len bytes, but a smaller number may be read, possibly
* zero. The number of bytes actually read is returned as an integer.
*
* This method blocks until input data is available, end of file is * detected, or an exception is thrown. * *
If b is null, a
* NullPointerException is thrown.
*
*
If off is negative, or len is negative, or
* off+len is greater than the length of the array
* b, then an IndexOutOfBoundsException is
* thrown.
*
*
If len is zero, then no bytes are read and
* 0 is returned; otherwise, there is an attempt to read at
* least one byte. If no byte is available because the stream is at end of
* file, the value -1 is returned; otherwise, at least one
* byte is read and stored into b.
*
*
The first byte read is stored into element b[off], the
* next one into b[off+1], and so on. The number of bytes read
* is, at most, equal to len. Let k be the number of
* bytes actually read; these bytes will be stored in elements
* b[off] through b[off+k-1],
* leaving elements b[off+k] through
* b[off+len-1] unaffected.
*
*
In every case, elements b[0] through
* b[off] and elements b[off+len] through
* b[b.length-1] are unaffected.
*
*
If the first byte cannot be read for any reason other than end of
* file, then an IOException is thrown. In particular, an
* IOException is thrown if the input stream has been closed.
*
*
The read(b, off, len) method
* for class InputStream simply calls the method
* read() repeatedly. If the first such call results in an
* IOException, that exception is returned from the call to
* the read(b, off, len) method. If
* any subsequent call to read() results in a
* IOException, the exception is caught and treated as if it
* were end of file; the bytes read up to that point are stored into
* b and the number of bytes read before the exception
* occurred is returned. Subclasses are encouraged to provide a more
* efficient implementation of this method.
*
* @param b the buffer into which the data is read.
* @param off the start offset in array b
* at which the data is written.
* @param len the maximum number of bytes to read.
* @return the total number of bytes read into the buffer, or
* -1 if there is no more data because the end of
* the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.InputStream#read()
*/
public int read(byte b[], int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if ((off < 0) || (off > b.length) || (len < 0) ||
((off + len) > b.length) || ((off + len) < 0)) {
throw new RuntimeException();
} else if (len == 0) {
return 0;
}
int c = read();
if (c == -1) {
return -1;
}
b[off] = (byte)c;
int i = 1;
try {
for (; i < len ; i++) {
c = read();
if (c == -1) {
break;
}
if (b != null) {
b[off + i] = (byte)c;
}
}
} catch (IOException ee) {
}
return i;
}
/**
* Skips over and discards n bytes of data from this input
* stream. The skip method may, for a variety of reasons, end
* up skipping over some smaller number of bytes, possibly 0.
* This may result from any of a number of conditions; reaching end of file
* before n bytes have been skipped is only one possibility.
* The actual number of bytes skipped is returned. If n is
* negative, no bytes are skipped.
*
*
The skip method of InputStream creates a
* byte array and then repeatedly reads into it until n bytes
* have been read or the end of the stream has been reached. Subclasses are
* encouraged to provide a more efficient implementation of this method.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if an I/O error occurs.
*/
public long skip(long n) throws IOException {
/*
long remaining = n;
int nr;
if (skipBuffer == null)
skipBuffer = new byte[SKIP_BUFFER_SIZE];
byte[] localSkipBuffer = skipBuffer;
if (n <= 0) {
return 0;
}
while (remaining > 0) {
nr = read(localSkipBuffer, 0,
(int) Math.min(SKIP_BUFFER_SIZE, remaining));
if (nr < 0) {
break;
}
remaining -= nr;
}
*/
return n;
}
/**
* Returns the number of bytes that can be read (or skipped over) from
* this input stream without blocking by the next caller of a method for
* this input stream. The next caller might be the same thread or or
* another thread.
*
*
The available method for class InputStream
* always returns 0.
*
*
This method should be overridden by subclasses. * * @return the number of bytes that can be read from this input stream * without blocking. * @exception IOException if an I/O error occurs. */ public int available() throws IOException { return 0; } /** * Closes this input stream and releases any system resources associated * with the stream. * *
The close method of InputStream does
* nothing.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {}
/**
* Marks the current position in this input stream. A subsequent call to
* the reset method repositions this stream at the last marked
* position so that subsequent reads re-read the same bytes.
*
*
The readlimit arguments tells this input stream to
* allow that many bytes to be read before the mark position gets
* invalidated.
*
*
The general contract of mark is that, if the method
* markSupported returns true, the stream somehow
* remembers all the bytes read after the call to mark and
* stands ready to supply those same bytes again if and whenever the method
* reset is called. However, the stream is not required to
* remember any data at all if more than readlimit bytes are
* read from the stream before reset is called.
*
*
The mark method of InputStream does
* nothing.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.InputStream#reset()
*/
public synchronized void mark(int readlimit) {}
/**
* Repositions this stream to the position at the time the
* mark method was last called on this input stream.
*
*
The general contract of reset is:
*
*
markSupported returns
* true, then:
*
* mark has not been called since
* the stream was created, or the number of bytes read from the stream
* since mark was last called is larger than the argument
* to mark at that last call, then an
* IOException might be thrown.
*
* IOException is not thrown, then the
* stream is reset to a state such that all the bytes read since the
* most recent call to mark (or since the start of the
* file, if mark has not been called) will be resupplied
* to subsequent callers of the read method, followed by
* any bytes that otherwise would have been the next input data as of
* the time of the call to reset. markSupported returns
* false, then:
*
* reset may throw an
* IOException.
*
* IOException is not thrown, then the stream
* is reset to a fixed state that depends on the particular type of the
* input stream and how it was created. The bytes that will be supplied
* to subsequent callers of the read method depend on the
* particular type of the input stream. The method reset for class InputStream
* does nothing and always throws an IOException.
*
* @exception IOException if this stream has not been marked or if the
* mark has been invalidated.
* @see java.io.InputStream#mark(int)
* @see java.io.IOException
*/
public synchronized void reset() throws IOException {
throw new IOException("mark/reset not supported");
}
/**
* Tests if this input stream supports the mark and
* reset methods. The markSupported method of
* InputStream returns false.
*
* @return true if this true type supports the mark and reset
* method; false otherwise.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return false;
}
}