273 lines
9.4 KiB
Java
273 lines
9.4 KiB
Java
/* InputStream.java -- Base class for input
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Copyright (C) 1998, 1999, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.io;
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/**
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* This abstract class forms the base of the hierarchy of classes that read
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* input as a stream of bytes. It provides a common set of methods for
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* reading bytes from streams. Subclasses implement and extend these
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* methods to read bytes from a particular input source such as a file
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* or network connection.
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*
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* @author Aaron M. Renn (arenn@urbanophile.com)
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* @author Warren Levy <warrenl@cygnus.com>
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*/
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public abstract class InputStream
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{
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/**
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* Default, no-arg, public constructor
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*/
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public InputStream()
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{
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}
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/**
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* This method returns the number of bytes that can be read from this
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* stream before a read can block. A return of 0 indicates that blocking
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* might (or might not) occur on the very next read attempt.
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* <p>
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* This method always returns 0 in this class
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*
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* @return The number of bytes that can be read before blocking could occur
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*
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* @exception IOException If an error occurs
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*/
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public int available() throws IOException
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{
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return 0;
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}
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/**
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* This method closes the stream. Any futher attempts to read from the
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* stream may generate an <code>IOException</code>
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* <p>
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* This method does nothing in this class, but subclasses may override
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* this method in order to provide additional functionality.
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*
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* @exception IOException If an error occurs, which can only happen
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* in a subclass
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*/
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public void close() throws IOException
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{
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// Do nothing
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}
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/**
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* This method marks a position in the input to which the stream can
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* be "reset" by calling the <code>reset()</code> method. The
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* parameter @code{readlimit} is the number of bytes that can be read
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* from the stream after setting the mark before the mark becomes
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* invalid. For example, if <code>mark()</code> is called with a
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* read limit of 10, then when 11 bytes of data are read from the
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* stream before the <code>reset()</code> method is called, then the
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* mark is invalid and the stream object instance is not required to
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* remember the mark.
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* <p>
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* This method does nothing in this class, but subclasses may override it
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* to provide mark/reset functionality.
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*
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* @param readLimit The number of bytes that can be read before the
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* mark becomes invalid
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*/
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public void mark(int readlimit)
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{
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// Do nothing
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}
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/**
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* This method returns a boolean that indicates whether the mark/reset
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* methods are supported in this class. Those methods can be used to
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* remember a specific point in the stream and reset the stream to that
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* point.
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* <p>
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* This method always returns <code>false</code> in this class, but
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* subclasses can override this method to return </code>true</code>
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* if they support mark/reset functionality.
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*
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* @return <code>true</code> if mark/reset functionality is
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* supported, <code>false</code> otherwise
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*/
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public boolean markSupported()
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{
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return false;
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}
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/**
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* This method reads an unsigned byte from the input stream and returns it
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* as an int in the range of 0-255. This method also will return -1 if
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* the end of the stream has been reached.
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* <p>
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* This method will block until the byte can be read.
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*
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* @return The byte read or -1 if end of stream
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*
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* @exception IOException If an error occurs
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*/
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public abstract int read() throws IOException;
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/**
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* This method reads bytes from a stream and stores them into a caller
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* supplied buffer. This method attempts to completely fill the buffer,
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* but can return before doing so. The actual number of bytes read is
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* returned as an int. A -1 is returned to indicate the end of the stream.
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* <p>
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* This method will block until some data can be read.
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* <p>
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* This method operates by calling an overloaded read method like so:
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* <code>read(b, 0, b.length)</code>
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*
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* @param b The buffer into which the bytes read will be stored.
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*
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* @return The number of bytes read or -1 if end of stream.
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*
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* @exception IOException If an error occurs.
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*/
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public int read(byte[] b) throws IOException
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{
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return read(b, 0, b.length);
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}
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/**
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* This method read bytes from a stream and stores them into a
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* caller supplied buffer. It starts storing the data at index
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* <code>off</code> into the buffer and attempts to read
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* <code>len</code> bytes. This method can return before reading the
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* number of bytes requested. The actual number of bytes read is
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* returned as an int. A -1 is returned to indicate the end of the
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* stream.
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* <p>
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* This method will block until some data can be read.
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* <p>
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* This method operates by calling the single byte <code>read()</code> method
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* in a loop until the desired number of bytes are read. The read loop
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* stops short if the end of the stream is encountered or if an IOException
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* is encountered on any read operation except the first. If the first
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* attempt to read a bytes fails, the IOException is allowed to propagate
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* upward. And subsequent IOException is caught and treated identically
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* to an end of stream condition. Subclasses can (and should if possible)
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* override this method to provide a more efficient implementation.
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*
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* @param b The array into which the bytes read should be stored
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* @param off The offset into the array to start storing bytes
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* @param len The requested number of bytes to read
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*
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* @return The actual number of bytes read, or -1 if end of stream.
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*
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* @exception IOException If an error occurs.
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*/
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public int read(byte[] b, int off, int len) throws IOException
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{
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if (off < 0 || len < 0 || off + len > b.length)
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throw new IndexOutOfBoundsException();
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if (b.length == 0)
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return 0;
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int i, ch;
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for (i = 0; i < len; ++i)
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try
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{
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if ((ch = read()) < 0)
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return i == 0 ? -1 : i; // EOF
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b[off + i] = (byte) ch;
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}
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catch (IOException ex)
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{
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// Only reading the first byte should cause an IOException.
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if (i == 0)
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throw ex;
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return i;
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}
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return i;
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}
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/**
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* This method resets a stream to the point where the
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* <code>mark()</code> method was called. Any bytes that were read
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* after the mark point was set will be re-read during subsequent
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* reads.
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* <p>
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* This method always throws an IOException in this class, but subclasses
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* can override this method if they provide mark/reset functionality.
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*
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* @exception IOException Always thrown for this class
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*/
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public void reset() throws IOException
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{
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throw new IOException("mark/reset not supported");
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}
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/**
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* This method skips the specified number of bytes in the stream. It
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* returns the actual number of bytes skipped, which may be less than the
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* requested amount.
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* <p>
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* This method reads and discards bytes into a byte array until the
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* specified number of bytes were skipped or until either the end of stream
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* is reached or a read attempt returns a short count. Subclasses can
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* override this metho to provide a more efficient implementation where
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* one exists.
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*
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* @param n The requested number of bytes to skip
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*
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* @return The actual number of bytes skipped.
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*
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* @exception IOException If an error occurs
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*/
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public long skip(long n) throws IOException
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{
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// Throw away n bytes by reading them into a temp byte[].
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// Limit the temp array to 2Kb so we don't grab too much memory.
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final int buflen = n > 2048 ? 2048 : (int) n;
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byte[] tmpbuf = new byte[buflen];
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final long origN = n;
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while (n > 0L)
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{
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int numread = read(tmpbuf, 0, n > buflen ? buflen : (int) n);
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if (numread <= 0)
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break;
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n -= numread;
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}
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return origN - n;
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}
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}
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