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