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;
+ }
+
+}