Back to index...

	/*
	* Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.io;

	/**
	* This abstract class is the superclass of all classes representing
	* an input stream of bytes.
	*
	* <p> Applications that need to define a subclass of <code>InputStream</code>
	* 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 {

	// MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
	// use when skipping.
	private static final int MAX_SKIP_BUFFER_SIZE = 2048;

	/**
	* Reads the next byte of data from the input stream. The value byte is
	* returned as an <code>int</code> in the range <code>0</code> to
	* <code>255</code>. If no byte is available because the end of the stream
	* has been reached, the value <code>-1</code> is returned. This method
	* blocks until input data is available, the end of the stream is detected,
	* or an exception is thrown.
	*
	* <p> A subclass must provide an implementation of this method.
	*
	* @return the next byte of data, or <code>-1</code> 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 <code>b</code>. 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.
	*
	* <p> If the length of <code>b</code> is zero, then no bytes are read and
	* <code>0</code> 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 <code>-1</code> is returned; otherwise, at
	* least one byte is read and stored into <code>b</code>.
	*
	* <p> The first byte read is stored into element <code>b[0]</code>, the
	* next one into <code>b[1]</code>, and so on. The number of bytes read is,
	* at most, equal to the length of <code>b</code>. Let <i>k</i> be the
	* number of bytes actually read; these bytes will be stored in elements
	* <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
	* leaving elements <code>b[</code><i>k</i><code>]</code> through
	* <code>b[b.length-1]</code> unaffected.
	*
	* <p> The <code>read(b)</code> method for class <code>InputStream</code>
	* has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
	*
	* @param b the buffer into which the data is read.
	* @return the total number of bytes read into the buffer, or
	* <code>-1</code> 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 <code>b</code> is <code>null</code>.
	* @see java.io.InputStream#read(byte[], int, int)
	*/
	public int read(byte b[]) throws IOException {
	return read(b, 0, b.length);
	}

	/**
	* Reads up to <code>len</code> bytes of data from the input stream into
	* an array of bytes. An attempt is made to read as many as
	* <code>len</code> bytes, but a smaller number may be read.
	* The number of bytes actually read is returned as an integer.
	*
	* <p> This method blocks until input data is available, end of file is
	* detected, or an exception is thrown.
	*
	* <p> If <code>len</code> is zero, then no bytes are read and
	* <code>0</code> 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 <code>-1</code> is returned; otherwise, at least one
	* byte is read and stored into <code>b</code>.
	*
	* <p> The first byte read is stored into element <code>b[off]</code>, the
	* next one into <code>b[off+1]</code>, and so on. The number of bytes read
	* is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
	* bytes actually read; these bytes will be stored in elements
	* <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
	* leaving elements <code>b[off+</code><i>k</i><code>]</code> through
	* <code>b[off+len-1]</code> unaffected.
	*
	* <p> In every case, elements <code>b[0]</code> through
	* <code>b[off]</code> and elements <code>b[off+len]</code> through
	* <code>b[b.length-1]</code> are unaffected.
	*
	* <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
	* for class <code>InputStream</code> simply calls the method
	* <code>read()</code> repeatedly. If the first such call results in an
	* <code>IOException</code>, that exception is returned from the call to
	* the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If
	* any subsequent call to <code>read()</code> results in a
	* <code>IOException</code>, the exception is caught and treated as if it
	* were end of file; the bytes read up to that point are stored into
	* <code>b</code> 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 <code>len</code> 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 <code>b</code>
	* 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
	* <code>-1</code> 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 <code>b</code> is <code>null</code>.
	* @exception IndexOutOfBoundsException If <code>off</code> is negative,
	* <code>len</code> is negative, or <code>len</code> is greater than
	* <code>b.length - off</code>
	* @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 <code>n</code> bytes of data from this input
	* stream. The <code>skip</code> method may, for a variety of reasons, end
	* up skipping over some smaller number of bytes, possibly <code>0</code>.
	* This may result from any of a number of conditions; reaching end of file
	* before <code>n</code> bytes have been skipped is only one possibility.
	* The actual number of bytes skipped is returned. If {@code n} is
	* negative, the {@code skip} method for class {@code InputStream} always
	* returns 0, and no bytes are skipped. Subclasses may handle the negative
	* value differently.
	*
	* <p> The <code>skip</code> method of this class creates a
	* byte array and then repeatedly reads into it until <code>n</code> 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 (n <= 0) {
	return 0;
	}

	int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
	byte[] skipBuffer = new byte[size];
	while (remaining > 0) {
	nr = read(skipBuffer, 0, (int)Math.min(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.
	*
	* <p> 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.
	*
	* <p> 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.
	*
	* <p> The {@code available} method for class {@code InputStream} always
	* returns {@code 0}.
	*
	* <p> 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.
	*
	* <p> The <code>close</code> method of <code>InputStream</code> 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 <code>reset</code> method repositions this stream at the last marked
	* position so that subsequent reads re-read the same bytes.
	*
	* <p> The <code>readlimit</code> arguments tells this input stream to
	* allow that many bytes to be read before the mark position gets
	* invalidated.
	*
	* <p> The general contract of <code>mark</code> is that, if the method
	* <code>markSupported</code> returns <code>true</code>, the stream somehow
	* remembers all the bytes read after the call to <code>mark</code> and
	* stands ready to supply those same bytes again if and whenever the method
	* <code>reset</code> is called. However, the stream is not required to
	* remember any data at all if more than <code>readlimit</code> bytes are
	* read from the stream before <code>reset</code> is called.
	*
	* <p> Marking a closed stream should not have any effect on the stream.
	*
	* <p> The <code>mark</code> method of <code>InputStream</code> 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
	* <code>mark</code> method was last called on this input stream.
	*
	* <p> The general contract of <code>reset</code> is:
	*
	* <ul>
	* <li> If the method <code>markSupported</code> returns
	* <code>true</code>, then:
	*
	* <ul><li> If the method <code>mark</code> has not been called since
	* the stream was created, or the number of bytes read from the stream
	* since <code>mark</code> was last called is larger than the argument
	* to <code>mark</code> at that last call, then an
	* <code>IOException</code> might be thrown.
	*
	* <li> If such an <code>IOException</code> is not thrown, then the
	* stream is reset to a state such that all the bytes read since the
	* most recent call to <code>mark</code> (or since the start of the
	* file, if <code>mark</code> has not been called) will be resupplied
	* to subsequent callers of the <code>read</code> method, followed by
	* any bytes that otherwise would have been the next input data as of
	* the time of the call to <code>reset</code>. </ul>
	*
	* <li> If the method <code>markSupported</code> returns
	* <code>false</code>, then:
	*
	* <ul><li> The call to <code>reset</code> may throw an
	* <code>IOException</code>.
	*
	* <li> If an <code>IOException</code> 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 <code>read</code> method depend on the
	* particular type of the input stream. </ul></ul>
	*
	* <p>The method <code>reset</code> for class <code>InputStream</code>
	* does nothing except throw an <code>IOException</code>.
	*
	* @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 <code>mark</code> and
	* <code>reset</code> methods. Whether or not <code>mark</code> and
	* <code>reset</code> are supported is an invariant property of a
	* particular input stream instance. The <code>markSupported</code> method
	* of <code>InputStream</code> returns <code>false</code>.
	*
	* @return <code>true</code> if this stream instance supports the mark
	* and reset methods; <code>false</code> otherwise.
	* @see java.io.InputStream#mark(int)
	* @see java.io.InputStream#reset()
	*/
	public boolean markSupported() {
	return false;
	}

	}

Back to index...