libjava/java/io/FileInputStream.java

   1 /* FileInputStream.java -- An input stream that reads from disk files.
   2    Copyright (C) 1998, 2002, 2003 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 java.nio.channels.FileChannel;
  42 import java.nio.channels.FileChannelImpl;
  43
  44 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  45  * "The Java Language Specification", ISBN 0-201-63451-1
  46  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  47  * Status:  Believed complete and correct.
  48  */
  49
  50 /**
  51  * This class is a stream that reads its bytes from a file.
  52  *
  53  * @author Aaron M. Renn <arenn@urbanophile.com>
  54  * @author Warren Levy <warrenl@cygnus.com>
  55  */
  56 public class FileInputStream extends InputStream
  57 {
  58   /**
  59    * This is the native file handle for the file this stream is reading from
  60    */
  61   private FileDescriptor fd;
  62
  63   private FileChannel ch;  /* cached associated file-channel */
  64
  65   /**
  66    * This method initializes a <code>FileInputStream</code> to read from the
  67    * specified named file.  A security check is first made to determine
  68    * whether or not access to this file is allowed.  This is done by
  69    * calling the <code>checkRead()</code> method of the
  70    * <code>SecurityManager</code>
  71    * (if one exists) with the name of this file.  An exception is thrown
  72    * if reading is not allowed.  If the file does not exist, an exception
  73    * is also thrown.
  74    *
  75    * @param name The name of the file this stream should read from
  76    *
  77    * @exception SecurityException If read access to the file is not allowed
  78    * @exception FileNotFoundException If the file does not exist.
  79    */
  80   public FileInputStream(String name) throws FileNotFoundException
  81   {
  82     SecurityManager s = System.getSecurityManager();
  83     if (s != null)
  84       s.checkRead(name);
  85
  86     fd = new FileDescriptor(name, FileDescriptor.READ);
  87   }
  88
  89   /**
  90    * This method initializes a <code>FileInputStream</code> to read from the
  91    * specified <code>File</code> object.  A security check is first
  92    * made to determine
  93    * whether or not access to this file is allowed.  This is done by
  94    * calling the <code>checkRead()</code> method of the
  95    * <code>SecurityManager</code>
  96    * (if one exists) with the name of this file.  An exception is thrown
  97    * if reading is not allowed.  If the file does not exist, an exception
  98    * is also thrown.
  99    *
 100    * @param file The <code>File</code> object this stream should read from
 101    *
 102    * @exception SecurityException If read access to the file is not allowed
 103    * @exception FileNotFoundException If the file does not exist.
 104    */
 105   public FileInputStream(File file) throws FileNotFoundException
 106   {
 107     this(file.getPath());
 108   }
 109
 110   /**
 111    * This method initializes a <code>FileInputStream</code> to read from the
 112    * specified <code>FileDescriptor</code> object.  A security
 113    * check is first made to
 114    * determine whether or not access to this file is allowed.  This is done by
 115    * calling the <code>checkRead()</code> method of the
 116    * <code>SecurityManager</code>
 117    * (if one exists) with the specified <code>FileDescriptor</code>
 118    * An exception is
 119    * thrown if reading is not allowed.
 120    *
 121    * @param fd The <code>FileDescriptor</code> object this stream
 122    * should read from
 123    *
 124    * @exception SecurityException If read access to the file is not allowed
 125    */
 126   public FileInputStream(FileDescriptor fdObj)
 127   {
 128     SecurityManager s = System.getSecurityManager();
 129     if (s != null)
 130       s.checkRead(fdObj);
 131
 132     fd = fdObj;
 133   }
 134
 135   /**
 136    * This method returns the number of bytes that can be read from this
 137    * stream before a read can block.  A return of 0 indicates that blocking
 138    * might (or might not) occur on the very next read attempt.
 139    * <p>
 140    * This method returns the number of unread bytes remaining in the file if
 141    * the descriptor being read from is an actual file.  If this method is
 142    * reading from a ''special'' file such a the standard input, this method
 143    * will return the appropriate value for the stream being read.
 144    * <p>
 145    * Be aware that reads on plain files that do not reside locally might
 146    * possibly block even if this method says they should not.  For example,
 147    * a remote server might crash, preventing an NFS mounted file from being
 148    * read.
 149    *
 150    * @return The number of bytes that can be read before blocking could occur
 151    *
 152    * @exception IOException If an error occurs
 153    */
 154   public int available() throws IOException
 155   {
 156     return fd.available();
 157   }
 158
 159   /**
 160    * This method closes the stream.  Any futher attempts to read from the
 161    * stream will likely generate an IOException since the underlying file
 162    * will be closed.
 163    *
 164    * @exception IOException If an error occurs.
 165    */
 166   public void close() throws IOException
 167   {
 168     if (fd.valid())
 169       fd.close();
 170   }
 171
 172   protected void finalize() throws IOException
 173   {
 174     // We don't actually need this, but we include it because it is
 175     // mentioned in the JCL.
 176   }
 177
 178   /**
 179    * This method returns a <code>FileDescriptor</code> object representing the
 180    * underlying native file handle of the file this stream is reading
 181    * from
 182    *
 183    * @return A <code>FileDescriptor</code> for this stream
 184    *
 185    * @exception IOException If an error occurs
 186    */
 187   public final FileDescriptor getFD() throws IOException
 188   {
 189     if (!fd.valid())
 190       throw new IOException();
 191     return fd;
 192   }
 193
 194   /**
 195    * This method reads an unsigned byte from the input stream and returns it
 196    * as an int in the range of 0-255.  This method also will return -1 if
 197    * the end of the stream has been reached.
 198    * <p>
 199    * This method will block until the byte can be read.
 200    *
 201    * @return The byte read or -1 if end of stream
 202    *
 203    * @exception IOException If an error occurs
 204    */
 205   public int read() throws IOException
 206   {
 207     return fd.read();
 208   }
 209
 210   /**
 211    * This method reads bytes from a stream and stores them into a caller
 212    * supplied buffer.  This method attempts to completely fill the buffer,
 213    * but can return before doing so.  The actual number of bytes read is
 214    * returned as an int.  A -1 is returned to indicate the end of the stream.
 215    * <p>
 216    * This method will block until some data can be read.
 217    * <p>
 218    * This method operates by calling an overloaded read method like so:
 219    * <code>read(buf, 0, buf.length)</code>
 220    *
 221    * @param buf The buffer into which the bytes read will be stored.
 222    *
 223    * @return The number of bytes read or -1 if end of stream.
 224    *
 225    * @exception IOException If an error occurs.
 226    */
 227   public int read(byte[] buf) throws IOException
 228   {
 229     return read(buf, 0, buf.length);
 230   }
 231
 232   /**
 233    * This method read bytes from a stream and stores them into a caller
 234    * supplied buffer.  It starts storing the data at index
 235    * <code>offset</code> into
 236    * the buffer and attempts to read <code>len</code> bytes.  This method can
 237    * return before reading the number of bytes requested.  The actual number
 238    * of bytes read is returned as an int.  A -1 is returned to indicate the
 239    * end of the stream.
 240    * <p>
 241    * This method will block until some data can be read.
 242    *
 243    * @param buf The array into which the bytes read should be stored
 244    * @param offset The offset into the array to start storing bytes
 245    * @param len The requested number of bytes to read
 246    *
 247    * @return The actual number of bytes read, or -1 if end of stream.
 248    *
 249    * @exception IOException If an error occurs.
 250    */
 251   public int read(byte[] buf, int offset, int len) throws IOException
 252   {
 253     if (offset < 0
 254         || len < 0
 255         || offset + len > buf.length)
 256       throw new ArrayIndexOutOfBoundsException();
 257
 258     return fd.read(buf, offset, len);
 259   }
 260
 261   /**
 262    * This method skips the specified number of bytes in the stream.  It
 263    * returns the actual number of bytes skipped, which may be less than the
 264    * requested amount.
 265    * <p>
 266    * @param numBytes The requested number of bytes to skip
 267    *
 268    * @return The actual number of bytes skipped.
 269    *
 270    * @exception IOException If an error occurs
 271    */
 272   public synchronized long skip (long numBytes) throws IOException
 273   {
 274     if (numBytes < 0)
 275       throw new IllegalArgumentException ("Can't skip negative bytes: " +
 276                                           numBytes);
 277
 278     if (numBytes == 0)
 279       return 0;
 280
 281     long curPos = fd.getFilePointer ();
 282     long newPos = fd.seek (numBytes, FileDescriptor.CUR, true);
 283     return newPos - curPos;
 284   }
 285
 286   /**
 287    * This method creates a java.nio.channels.FileChannel.
 288    * Nio does not allow one to create a file channel directly.
 289    * A file channel must be created by first creating an instance of
 290    * Input/Output/RandomAccessFile and invoking the getChannel() method on it.
 291    */
 292   public synchronized FileChannel getChannel ()
 293   {
 294     if (ch == null)
 295       ch = new FileChannelImpl (fd, false, this);
 296
 297     return ch;
 298   }
 299
 300 } // class FileInputStream
 301