001/* FileInputStream.java -- An input stream that reads from disk files.
002   Copyright (C) 1998, 2002, 2003, 2004, 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010 
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.io;
040
041import gnu.java.nio.channels.FileChannelImpl;
042
043import java.nio.channels.FileChannel;
044
045/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
046 * "The Java Language Specification", ISBN 0-201-63451-1
047 * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
048 * Status:  Believed complete and correct.
049 */
050 
051/**
052 * This class is a stream that reads its bytes from a file. 
053 *
054 * @author Aaron M. Renn (arenn@urbanophile.com)
055 * @author Warren Levy (warrenl@cygnus.com)
056 */
057public class FileInputStream extends InputStream
058{
059  /**
060   * This is the native file handle for the file this stream is reading from
061   */
062  private FileDescriptor fd;
063
064  private FileChannelImpl ch;
065
066  /**
067   * This method initializes a <code>FileInputStream</code> to read from the
068   * specified named file.  A security check is first made to determine
069   * whether or not access to this file is allowed.  This is done by
070   * calling the <code>checkRead()</code> method of the 
071   * <code>SecurityManager</code>
072   * (if one exists) with the name of this file.  An exception is thrown
073   * if reading is not allowed.  If the file does not exist, an exception
074   * is also thrown.
075   *
076   * @param name The name of the file this stream should read from
077   *
078   * @exception SecurityException If read access to the file is not allowed
079   * @exception FileNotFoundException If the file does not exist 
080   * or if it is a directory
081   */
082  public FileInputStream(String name) throws FileNotFoundException
083  {
084    this(new File(name));
085  }
086
087  /**
088   * This method initializes a <code>FileInputStream</code> to read from the
089   * specified <code>File</code> object.  A security check is first
090   * made to determine
091   * whether or not access to this file is allowed.  This is done by
092   * calling the <code>checkRead()</code> method of the
093   * <code>SecurityManager</code>
094   * (if one exists) with the name of this file.  An exception is thrown
095   * if reading is not allowed.  If the file does not exist, an exception
096   * is also thrown.
097   *
098   * @param file The <code>File</code> object this stream should read from
099   *
100   * @exception SecurityException If read access to the file is not allowed
101   * @exception FileNotFoundException If the file does not exist
102   * or if it is a directory.
103   */
104  public FileInputStream(File file) throws FileNotFoundException
105  {
106    SecurityManager s = System.getSecurityManager();
107    if (s != null)
108      s.checkRead(file.getPath());
109
110    ch = FileChannelImpl.create(file, FileChannelImpl.READ);
111  }
112
113  /**
114   * This method initializes a <code>FileInputStream</code> to read from the
115   * specified <code>FileDescriptor</code> object.  A security
116   * check is first made to
117   * determine whether or not access to this file is allowed.  This is done by
118   * calling the <code>checkRead()</code> method of the 
119   * <code>SecurityManager</code>
120   * (if one exists) with the specified <code>FileDescriptor</code>  
121   * An exception is 
122   * thrown if reading is not allowed.
123   *
124   * @param fdObj The <code>FileDescriptor</code> object this stream 
125   * should read from
126   *
127   * @exception SecurityException If read access to the file is not allowed
128   */
129  public FileInputStream(FileDescriptor fdObj)
130  {
131    SecurityManager s = System.getSecurityManager();
132    if (s != null)
133      s.checkRead(fdObj);
134
135    fd = fdObj;
136    ch = (FileChannelImpl) fdObj.channel;
137  }
138
139  FileInputStream(FileChannelImpl ch)
140  {
141    this.ch = ch;
142  }
143
144  /**
145   * This method returns the number of bytes that can be read from this
146   * stream before a read can block.  A return of 0 indicates that blocking
147   * might (or might not) occur on the very next read attempt.
148   * <p>
149   * This method returns the number of unread bytes remaining in the file if
150   * the descriptor being read from is an actual file.  If this method is
151   * reading from a ''special'' file such a the standard input, this method
152   * will return the appropriate value for the stream being read.
153   * <p>
154   * Be aware that reads on plain files that do not reside locally might
155   * possibly block even if this method says they should not.  For example,
156   * a remote server might crash, preventing an NFS mounted file from being
157   * read.
158   *
159   * @return The number of bytes that can be read before blocking could occur
160   *
161   * @exception IOException If an error occurs
162   */
163  public int available() throws IOException
164  {
165    return ch.available();
166  }
167
168  /**
169   * This method closes the stream.  Any futher attempts to read from the
170   * stream will likely generate an IOException since the underlying file
171   * will be closed.
172   *
173   * @exception IOException If an error occurs.
174   */
175  public void close() throws IOException
176  {
177    ch.close();
178  }
179
180  protected void finalize() throws IOException
181  {
182    // We don't actually need this, but we include it because it is
183    // mentioned in the JCL.
184  }
185
186  /**
187   * This method returns a <code>FileDescriptor</code> object representing the
188   * underlying native file handle of the file this stream is reading
189   * from
190   *
191   * @return A <code>FileDescriptor</code> for this stream
192   *
193   * @exception IOException If an error occurs
194   */
195  public final FileDescriptor getFD() throws IOException
196  {
197    synchronized (this)
198      {
199        if (fd == null)
200          fd = new FileDescriptor (ch);
201        return fd;
202      }
203  }
204
205  /**
206   * This method reads an unsigned byte from the input stream and returns it
207   * as an int in the range of 0-255.  This method also will return -1 if
208   * the end of the stream has been reached.
209   * <p>
210   * This method will block until the byte can be read.
211   *
212   * @return The byte read or -1 if end of stream
213   *
214   * @exception IOException If an error occurs
215   */
216  public int read() throws IOException
217  {
218    return ch.read();
219  }
220
221  /**
222   * This method reads bytes from a stream and stores them into a caller
223   * supplied buffer.  This method attempts to completely fill the buffer,
224   * but can return before doing so.  The actual number of bytes read is
225   * returned as an int.  A -1 is returned to indicate the end of the stream.
226   * <p>
227   * This method will block until some data can be read.
228   * <p>
229   * This method operates by calling an overloaded read method like so:
230   * <code>read(buf, 0, buf.length)</code>
231   *
232   * @param buf The buffer into which the bytes read will be stored.
233   *
234   * @return The number of bytes read or -1 if end of stream.
235   *
236   * @exception IOException If an error occurs.
237   */
238  public int read(byte[] buf) throws IOException
239  {
240    return read(buf, 0, buf.length);
241  }
242
243  /**
244   * This method read bytes from a stream and stores them into a caller
245   * supplied buffer.  It starts storing the data at index 
246   * <code>offset</code> into
247   * the buffer and attempts to read <code>len</code> bytes.  This method can
248   * return before reading the number of bytes requested.  The actual number
249   * of bytes read is returned as an int.  A -1 is returned to indicate the
250   * end of the stream.
251   * <p>
252   * This method will block until some data can be read.
253   *
254   * @param buf The array into which the bytes read should be stored
255   * @param offset The offset into the array to start storing bytes
256   * @param len The requested number of bytes to read
257   *
258   * @return The actual number of bytes read, or -1 if end of stream.
259   *
260   * @exception IOException If an error occurs.
261   */
262  public int read(byte[] buf, int offset, int len) throws IOException
263  {
264    if (offset < 0
265        || len < 0
266        || offset + len > buf.length)
267      throw new ArrayIndexOutOfBoundsException();
268
269    return ch.read(buf, offset, len);
270  }
271
272  /**
273   * This method skips the specified number of bytes in the stream.  It
274   * returns the actual number of bytes skipped, which may be less than the
275   * requested amount.
276   * <p>
277   * @param numBytes The requested number of bytes to skip
278   *
279   * @return The actual number of bytes skipped.
280   *
281   * @exception IOException If an error occurs
282   */
283  public synchronized long skip (long numBytes) throws IOException
284  {
285    if (numBytes < 0)
286      throw new IllegalArgumentException ("Can't skip negative bytes: " + 
287                                          numBytes);
288
289    if (numBytes == 0)
290      return 0;
291
292    long oldPos = ch.position ();
293    ch.position(oldPos + numBytes);
294    return ch.position() - oldPos;
295  }
296
297  /**
298   * This method creates a java.nio.channels.FileChannel.
299   * Nio does not allow one to create a file channel directly.
300   * A file channel must be created by first creating an instance of
301   * Input/Output/RandomAccessFile and invoking the getChannel() method on it.
302   */
303  public synchronized FileChannel getChannel () 
304  {
305    return ch;
306  }
307
308} // class FileInputStream
309