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
- * @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 implements Closeable {
-
- // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer
- private static final int SKIP_BUFFER_SIZE = 2048;
- // 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 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 the
- * end of the 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.
- *
- *
The read(b) method for class InputStream
- * has the same effect as:
read(b, 0, b.length) -1 if there is no more data because the end of
- * the stream has been reached.
- * @exception IOException If the first byte cannot be read for any reason
- * other than the end of the file, if the input stream has been closed, or
- * if some other I/O error occurs.
- * @exception NullPointerException if b is null.
- * @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.
- * 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 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.
- *
- *
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. The default implementation of this method blocks
- * until the requested amount of input data len has been read,
- * end of file is detected, or an exception is thrown. 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 the first byte cannot be read for any reason
- * other than end of file, or if the input stream has been closed, or if
- * some other I/O error occurs.
- * @exception NullPointerException If b is null.
- * @exception IndexOutOfBoundsException If off is negative,
- * len is negative, or len is greater than
- * b.length - off
- * @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 || len < 0 || len > b.length - off) {
- throw new IndexOutOfBoundsException();
- } 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;
- }
- 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 this class 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.
- * For instance, the implementation may depend on the ability to seek.
- *
- * @param n the number of bytes to be skipped.
- * @return the actual number of bytes skipped.
- * @exception IOException if the stream does not support seek,
- * or if some other 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 - remaining;
- }
-
- /**
- * 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.
- *
- *
Note that while some implementations of {@code InputStream} will return - * the total number of bytes in the stream, many will not. It is - * never correct to use the return value of this method to allocate - * a buffer intended to hold all data in this stream. - * - *
A subclass' implementation of this method may choose to throw an - * {@link IOException} if this input stream has been closed by - * invoking the {@link #close()} method. - * - *
The {@code available} method for class {@code InputStream} always - * returns {@code 0}. - * - *
This method should be overridden by subclasses. - * - * @return an estimate of the number of bytes that can be read (or skipped - * over) from this input stream without blocking or {@code 0} when - * it reaches the end of the input stream. - * @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.
- *
- *
Marking a closed stream should not have any effect on the stream. - * - *
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 except throw 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. Whether or not mark and
- * reset are supported is an invariant property of a
- * particular input stream instance. The markSupported method
- * of InputStream returns false.
- *
- * @return true if this stream instance supports the mark
- * and reset methods; false otherwise.
- * @see java.io.InputStream#mark(int)
- * @see java.io.InputStream#reset()
- */
- public boolean markSupported() {
- return false;
- }
-
-}