old-autovect-branch/libjava/java/io/FileInputStream.java

   1 /* FileInputStream.java -- An input stream that reads from disk files.
   2    Copyright (C) 1998, 2002, 2003, 2004, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.io;
  40
  41 import gnu.java.nio.channels.FileChannelImpl;
  42
  43 import java.nio.channels.FileChannel;
  44
  45 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  46  * "The Java Language Specification", ISBN 0-201-63451-1
  47  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  48  * Status:  Believed complete and correct.
  49  */
  50
  51 /**
  52  * This class is a stream that reads its bytes from a file.
  53  *
  54  * @author Aaron M. Renn (arenn@urbanophile.com)
  55  * @author Warren Levy (warrenl@cygnus.com)
  56  */
  57 public class FileInputStream extends InputStream
  58 {
  59   /**
  60    * This is the native file handle for the file this stream is reading from
  61    */
  62   private FileDescriptor fd;
  63
  64   private FileChannelImpl ch;
  65
  66   /**
  67    * This method initializes a <code>FileInputStream</code> to read from the
  68    * specified named file.  A security check is first made to determine
  69    * whether or not access to this file is allowed.  This is done by
  70    * calling the <code>checkRead()</code> method of the
  71    * <code>SecurityManager</code>
  72    * (if one exists) with the name of this file.  An exception is thrown
  73    * if reading is not allowed.  If the file does not exist, an exception
  74    * is also thrown.
  75    *
  76    * @param name The name of the file this stream should read from
  77    *
  78    * @exception SecurityException If read access to the file is not allowed
  79    * @exception FileNotFoundException If the file does not exist
  80    * or if it is a directory
  81    */
  82   public FileInputStream(String name) throws FileNotFoundException
  83   {
  84     this(new File(name));
  85   }
  86
  87   /**
  88    * This method initializes a <code>FileInputStream</code> to read from the
  89    * specified <code>File</code> object.  A security check is first
  90    * made to determine
  91    * whether or not access to this file is allowed.  This is done by
  92    * calling the <code>checkRead()</code> method of the
  93    * <code>SecurityManager</code>
  94    * (if one exists) with the name of this file.  An exception is thrown
  95    * if reading is not allowed.  If the file does not exist, an exception
  96    * is also thrown.
  97    *
  98    * @param file The <code>File</code> object this stream should read from
  99    *
 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 = new FileChannelImpl (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