001    /* InputStream.java -- Base class for input
002       Copyright (C) 1998, 1999, 2001, 2004, 2005 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010     
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038     
039    package java.io;
040    
041    /**
042      * This abstract class forms the base of the hierarchy of classes that read
043      * input as a stream of bytes.  It provides a common set of methods for
044      * reading bytes from streams.  Subclasses implement and extend these
045      * methods to read bytes from a particular input source such as a file
046      * or network connection.
047      *
048      * @author Aaron M. Renn (arenn@urbanophile.com)
049      * @author Warren Levy (warrenl@cygnus.com)
050      */
051    public abstract class InputStream implements Closeable
052    {
053      /**
054       * Default, no-arg, public constructor
055       */
056      public InputStream()
057      {
058      }
059    
060      /**
061       * This method returns the number of bytes that can be read from this
062       * stream before a read can block.  A return of 0 indicates that blocking
063       * might (or might not) occur on the very next read attempt.
064       * <p>
065       * This method always returns 0 in this class
066       *
067       * @return The number of bytes that can be read before blocking could occur
068       *
069       * @exception IOException If an error occurs
070       */
071      public int available() throws IOException
072      {
073        return 0;
074      }
075    
076      /**
077       * This method closes the stream.  Any futher attempts to read from the
078       * stream may generate an <code>IOException</code>
079       * <p>
080       * This method does nothing in this class, but subclasses may override
081       * this method in order to provide additional functionality.
082       *
083       * @exception IOException If an error occurs, which can only happen
084       * in a subclass
085       */
086      public void close() throws IOException
087      {
088        // Do nothing
089      }
090    
091      /**
092       * This method marks a position in the input to which the stream can
093       * be "reset" by calling the <code>reset()</code> method.  The
094       * parameter @code{readlimit} is the number of bytes that can be read
095       * from the stream after setting the mark before the mark becomes
096       * invalid.  For example, if <code>mark()</code> is called with a
097       * read limit of 10, then when 11 bytes of data are read from the
098       * stream before the <code>reset()</code> method is called, then the
099       * mark is invalid and the stream object instance is not required to
100       * remember the mark.
101       * <p>
102       * This method does nothing in this class, but subclasses may override it
103       * to provide mark/reset functionality.
104       *
105       * @param readLimit The number of bytes that can be read before the
106       *                  mark becomes invalid
107       */
108      public void mark(int readLimit)
109      {
110        // Do nothing
111      }
112    
113      /**
114       * This method returns a boolean that indicates whether the mark/reset
115       * methods are supported in this class.  Those methods can be used to
116       * remember a specific point in the stream and reset the stream to that
117       * point.
118       * <p>
119       * This method always returns <code>false</code> in this class, but
120       * subclasses can override this method to return <code>true</code>
121       * if they support mark/reset functionality.
122       *
123       * @return <code>true</code> if mark/reset functionality is
124       * supported, <code>false</code> otherwise 
125       */
126      public boolean markSupported()
127      {
128        return false;
129      }
130    
131      /**
132       * This method reads an unsigned byte from the input stream and returns it
133       * as an int in the range of 0-255.  This method also will return -1 if
134       * the end of the stream has been reached.
135       * <p>
136       * This method will block until the byte can be read.
137       *
138       * @return The byte read or -1 if end of stream
139       *
140       * @exception IOException If an error occurs
141       */
142      public abstract int read() throws IOException;
143    
144      /**
145       * This method reads bytes from a stream and stores them into a caller
146       * supplied buffer.  This method attempts to completely fill the buffer,
147       * but can return before doing so.  The actual number of bytes read is
148       * returned as an int.  A -1 is returned to indicate the end of the stream.
149       * <p>
150       * This method will block until some data can be read.
151       * <p>
152       * This method operates by calling an overloaded read method like so:
153       * <code>read(b, 0, b.length)</code>
154       *
155       * @param b The buffer into which the bytes read will be stored.
156       *
157       * @return The number of bytes read or -1 if end of stream.
158       *
159       * @exception IOException If an error occurs.
160       */
161      public int read(byte[] b) throws IOException
162      {
163        return read(b, 0, b.length);
164      }
165    
166      /**
167       * This method read bytes from a stream and stores them into a
168       * caller supplied buffer.  It starts storing the data at index
169       * <code>off</code> into the buffer and attempts to read
170       * <code>len</code> bytes.  This method can return before reading the
171       * number of bytes requested.  The actual number of bytes read is
172       * returned as an int.  A -1 is returned to indicate the end of the
173       * stream.
174       *  <p>
175       * This method will block until some data can be read.
176       * <p>
177       * This method operates by calling the single byte <code>read()</code> method
178       * in a loop until the desired number of bytes are read.  The read loop
179       * stops short if the end of the stream is encountered or if an IOException
180       * is encountered on any read operation except the first.  If the first
181       * attempt to read a bytes fails, the IOException is allowed to propagate
182       * upward.  And subsequent IOException is caught and treated identically
183       * to an end of stream condition.  Subclasses can (and should if possible)
184       * override this method to provide a more efficient implementation.
185       *
186       * @param b The array into which the bytes read should be stored
187       * @param off The offset into the array to start storing bytes
188       * @param len The requested number of bytes to read
189       *
190       * @return The actual number of bytes read, or -1 if end of stream.
191       *
192       * @exception IOException If an error occurs.
193       */
194      public int read(byte[] b, int off, int len) throws IOException
195      {
196        if (off < 0 || len < 0 || b.length - off < len)
197          throw new IndexOutOfBoundsException();
198    
199        int i, ch;
200    
201        for (i = 0; i < len; ++i)
202          try
203            {
204              if ((ch = read()) < 0)
205                return i == 0 ? -1 : i;             // EOF
206              b[off + i] = (byte) ch;
207            }
208          catch (IOException ex)
209            {
210              // Only reading the first byte should cause an IOException.
211              if (i == 0)
212                throw ex;
213              return i;
214            }
215    
216        return i;
217      }
218    
219      /**
220       * This method resets a stream to the point where the
221       * <code>mark()</code> method was called.  Any bytes that were read
222       * after the mark point was set will be re-read during subsequent
223       * reads.
224       * <p>
225       * This method always throws an IOException in this class, but subclasses
226       * can override this method if they provide mark/reset functionality.
227       *
228       * @exception IOException Always thrown for this class
229       */
230      public void reset() throws IOException
231      {
232        throw new IOException("mark/reset not supported");
233      }
234    
235      /**
236       * This method skips the specified number of bytes in the stream.  It
237       * returns the actual number of bytes skipped, which may be less than the
238       * requested amount.
239       * <p>
240       * This method reads and discards bytes into a byte array until the
241       * specified number of bytes were skipped or until either the end of stream
242       * is reached or a read attempt returns a short count.  Subclasses can
243       * override this metho to provide a more efficient implementation where
244       * one exists.
245       *
246       * @param n The requested number of bytes to skip
247       *
248       * @return The actual number of bytes skipped.
249       *
250       * @exception IOException If an error occurs
251       */
252      public long skip(long n) throws IOException
253      {
254        // Throw away n bytes by reading them into a temp byte[].
255        // Limit the temp array to 2Kb so we don't grab too much memory.
256        final int buflen = n > 2048 ? 2048 : (int) n;
257        byte[] tmpbuf = new byte[buflen];
258        final long origN = n;
259    
260        while (n > 0L)
261          {
262            int numread = read(tmpbuf, 0, n > buflen ? buflen : (int) n);
263            if (numread <= 0)
264              break;
265            n -= numread;
266          }
267    
268        return origN - n;
269      }
270    }