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., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 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    */
  81   public FileInputStream(String name) throws FileNotFoundException
  82   {
  83     this(new File(name));
  84   }
  85
  86   /**
  87    * This method initializes a <code>FileInputStream</code> to read from the
  88    * specified <code>File</code> object.  A security check is first
  89    * made to determine
  90    * whether or not access to this file is allowed.  This is done by
  91    * calling the <code>checkRead()</code> method of the
  92    * <code>SecurityManager</code>
  93    * (if one exists) with the name of this file.  An exception is thrown
  94    * if reading is not allowed.  If the file does not exist, an exception
  95    * is also thrown.
  96    *
  97    * @param file The <code>File</code> object this stream should read from
  98    *
  99    * @exception SecurityException If read access to the file is not allowed
 100    * @exception FileNotFoundException If the file does not exist.
 101    */
 102   public FileInputStream(File file) throws FileNotFoundException
 103   {
 104     SecurityManager s = System.getSecurityManager();
 105     if (s != null)
 106       s.checkRead(file.getPath());
 107
 108     if (file.isDirectory())
 109       throw new FileNotFoundException(file.getPath() + " is a directory");
 110
 111     ch = new FileChannelImpl (file.getPath(), FileChannelImpl.READ);
 112   }
 113
 114   /**
 115    * This method initializes a <code>FileInputStream</code> to read from the
 116    * specified <code>FileDescriptor</code> object.  A security
 117    * check is first made to
 118    * determine whether or not access to this file is allowed.  This is done by
 119    * calling the <code>checkRead()</code> method of the
 120    * <code>SecurityManager</code>
 121    * (if one exists) with the specified <code>FileDescriptor</code>
 122    * An exception is
 123    * thrown if reading is not allowed.
 124    *
 125    * @param fdObj The <code>FileDescriptor</code> object this stream
 126    * should read from
 127    *
 128    * @exception SecurityException If read access to the file is not allowed
 129    */
 130   public FileInputStream(FileDescriptor fdObj)
 131   {
 132     SecurityManager s = System.getSecurityManager();
 133     if (s != null)
 134       s.checkRead(fdObj);
 135
 136     fd = fdObj;
 137     ch = (FileChannelImpl) fdObj.channel;
 138   }
 139
 140   FileInputStream(FileChannelImpl ch)
 141   {
 142     this.ch = ch;
 143   }
 144
 145   /**
 146    * This method returns the number of bytes that can be read from this
 147    * stream before a read can block.  A return of 0 indicates that blocking
 148    * might (or might not) occur on the very next read attempt.
 149    * <p>
 150    * This method returns the number of unread bytes remaining in the file if
 151    * the descriptor being read from is an actual file.  If this method is
 152    * reading from a ''special'' file such a the standard input, this method
 153    * will return the appropriate value for the stream being read.
 154    * <p>
 155    * Be aware that reads on plain files that do not reside locally might
 156    * possibly block even if this method says they should not.  For example,
 157    * a remote server might crash, preventing an NFS mounted file from being
 158    * read.
 159    *
 160    * @return The number of bytes that can be read before blocking could occur
 161    *
 162    * @exception IOException If an error occurs
 163    */
 164   public int available() throws IOException
 165   {
 166     return ch.available();
 167   }
 168
 169   /**
 170    * This method closes the stream.  Any futher attempts to read from the
 171    * stream will likely generate an IOException since the underlying file
 172    * will be closed.
 173    *
 174    * @exception IOException If an error occurs.
 175    */
 176   public void close() throws IOException
 177   {
 178     ch.close();
 179   }
 180
 181   protected void finalize() throws IOException
 182   {
 183     // We don't actually need this, but we include it because it is
 184     // mentioned in the JCL.
 185   }
 186
 187   /**
 188    * This method returns a <code>FileDescriptor</code> object representing the
 189    * underlying native file handle of the file this stream is reading
 190    * from
 191    *
 192    * @return A <code>FileDescriptor</code> for this stream
 193    *
 194    * @exception IOException If an error occurs
 195    */
 196   public final FileDescriptor getFD() throws IOException
 197   {
 198     synchronized (this)
 199       {
 200         if (fd == null)
 201           fd = new FileDescriptor (ch);
 202         return fd;
 203       }
 204   }
 205
 206   /**
 207    * This method reads an unsigned byte from the input stream and returns it
 208    * as an int in the range of 0-255.  This method also will return -1 if
 209    * the end of the stream has been reached.
 210    * <p>
 211    * This method will block until the byte can be read.
 212    *
 213    * @return The byte read or -1 if end of stream
 214    *
 215    * @exception IOException If an error occurs
 216    */
 217   public int read() throws IOException
 218   {
 219     return ch.read();
 220   }
 221
 222   /**
 223    * This method reads bytes from a stream and stores them into a caller
 224    * supplied buffer.  This method attempts to completely fill the buffer,
 225    * but can return before doing so.  The actual number of bytes read is
 226    * returned as an int.  A -1 is returned to indicate the end of the stream.
 227    * <p>
 228    * This method will block until some data can be read.
 229    * <p>
 230    * This method operates by calling an overloaded read method like so:
 231    * <code>read(buf, 0, buf.length)</code>
 232    *
 233    * @param buf The buffer into which the bytes read will be stored.
 234    *
 235    * @return The number of bytes read or -1 if end of stream.
 236    *
 237    * @exception IOException If an error occurs.
 238    */
 239   public int read(byte[] buf) throws IOException
 240   {
 241     return read(buf, 0, buf.length);
 242   }
 243
 244   /**
 245    * This method read bytes from a stream and stores them into a caller
 246    * supplied buffer.  It starts storing the data at index
 247    * <code>offset</code> into
 248    * the buffer and attempts to read <code>len</code> bytes.  This method can
 249    * return before reading the number of bytes requested.  The actual number
 250    * of bytes read is returned as an int.  A -1 is returned to indicate the
 251    * end of the stream.
 252    * <p>
 253    * This method will block until some data can be read.
 254    *
 255    * @param buf The array into which the bytes read should be stored
 256    * @param offset The offset into the array to start storing bytes
 257    * @param len The requested number of bytes to read
 258    *
 259    * @return The actual number of bytes read, or -1 if end of stream.
 260    *
 261    * @exception IOException If an error occurs.
 262    */
 263   public int read(byte[] buf, int offset, int len) throws IOException
 264   {
 265     if (offset < 0
 266         || len < 0
 267         || offset + len > buf.length)
 268       throw new ArrayIndexOutOfBoundsException();
 269
 270     return ch.read(buf, offset, len);
 271   }
 272
 273   /**
 274    * This method skips the specified number of bytes in the stream.  It
 275    * returns the actual number of bytes skipped, which may be less than the
 276    * requested amount.
 277    * <p>
 278    * @param numBytes The requested number of bytes to skip
 279    *
 280    * @return The actual number of bytes skipped.
 281    *
 282    * @exception IOException If an error occurs
 283    */
 284   public synchronized long skip (long numBytes) throws IOException
 285   {
 286     if (numBytes < 0)
 287       throw new IllegalArgumentException ("Can't skip negative bytes: " +
 288                                           numBytes);
 289
 290     if (numBytes == 0)
 291       return 0;
 292
 293     long oldPos = ch.position ();
 294     ch.position(oldPos + numBytes);
 295     return ch.position() - oldPos;
 296   }
 297
 298   /**
 299    * This method creates a java.nio.channels.FileChannel.
 300    * Nio does not allow one to create a file channel directly.
 301    * A file channel must be created by first creating an instance of
 302    * Input/Output/RandomAccessFile and invoking the getChannel() method on it.
 303    */
 304   public synchronized FileChannel getChannel ()
 305   {
 306     return ch;
 307   }
 308
 309 } // class FileInputStream
 310