SharedFileInputStream


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21  
22  /*
23   * @(#)SharedFileInputStream.java   1.8 05/08/29
24   *
25   * Copyright 1994-2005 Sun Microsystems, Inc. All Rights Reserved.
26   */
27  
28  package javax.mail.util;
29  
30  import java.io.*;
31  import javax.mail.internet.SharedInputStream  ;
32  
33  /**
34   * A <code>SharedFileInputStream</code> is a
35   * <code>BufferedInputStream</code> that buffers
36   * data from the file and supports the <code>mark</code>
37   * and <code>reset</code> methods.  It also supports the
38   * <code>newStream</code> method that allows you to create
39   * other streams that represent subsets of the file.
40   * A <code>RandomAccessFile</code> object is used to
41   * access the file data.
42   *
43   * @author  Bill Shannon
44   * @since   JavaMail 1.4
45   */
46  public class SharedFileInputStream extends BufferedInputStream
47                  implements SharedInputStream   {
48  
49      private static int defaultBufferSize = 2048;
50  
51      /**
52       * The file containing the data.
53       * Shared by all related SharedFileInputStreams.
54       */
55      protected RandomAccessFile in;
56  
57      /**
58       * The normal size of the read buffer.
59       */
60      protected int bufsize;
61  
62      /**
63       * The file offset that corresponds to the first byte in
64       * the read buffer.
65       */
66      protected long bufpos;
67  
68      /**
69       * The file offset of the start of data in this subset of the file.
70       */
71      protected long start = 0;
72  
73      /**
74       * The amount of data in this subset of the file.
75       */
76      protected long datalen;
77  
78      /**
79       * True if this is a top level stream created directly by "new".
80       * False if this is a derived stream created by newStream.
81       */
82      private boolean master = true;
83  
84      /**
85       * A shared class that keeps track of the references
86       * to a particular file so it can be closed when the
87       * last reference is gone.
88       */
89      class SharedFile {
90      private int cnt;
91      private RandomAccessFile in;
92  
93      SharedFile(String   file) throws IOException {
94          this.in = new RandomAccessFile(file, "r");
95      }
96  
97      SharedFile(File file) throws IOException {
98          this.in = new RandomAccessFile(file, "r");
99      }
100 
101     public RandomAccessFile open() {
102         cnt++;
103         return in;
104     }
105 
106     public synchronized void close() throws IOException {
107         if (cnt > 0 && --cnt <= 0)
108         in.close();
109     }
110 
111     public synchronized void forceClose() throws IOException {
112         if (cnt > 0) {
113         // normal case, close exceptions propagated
114         cnt = 0;
115         in.close();
116         } else {
117         // should already be closed, ignore exception
118         try {
119             in.close();
120         } catch (IOException ioex) { }
121         }
122     }
123 
124     protected void finalize() throws Throwable   {
125         super.finalize();
126         in.close();
127     }
128     }
129 
130     private SharedFile sf;
131 
132     /**
133      * Check to make sure that this stream has not been closed
134      */
135     private void ensureOpen() throws IOException {
136     if (in == null)
137         throw new IOException("Stream closed");
138     }
139 
140     /**
141      * Creates a <code>SharedFileInputStream</code>
142      * for the file.
143      *
144      * @param   file   the file
145      */
146     public SharedFileInputStream(File file) throws IOException {
147     this(file, defaultBufferSize);
148     }
149 
150     /**
151      * Creates a <code>SharedFileInputStream</code>
152      * for the named file
153      *
154      * @param   file   the file
155      */
156     public SharedFileInputStream(String   file) throws IOException {
157     this(file, defaultBufferSize);
158     }
159 
160     /**
161      * Creates a <code>SharedFileInputStream</code>
162      * with the specified buffer size.
163      *
164      * @param   file    the file
165      * @param   size   the buffer size.
166      * @exception IllegalArgumentException if size <= 0.
167      */
168     public SharedFileInputStream(File file, int size) throws IOException {
169     super(null);    // XXX - will it NPE?
170         if (size <= 0)
171             throw new IllegalArgumentException  ("Buffer size <= 0");
172     init(new SharedFile(file), size);
173     }
174 
175     /**
176      * Creates a <code>SharedFileInputStream</code>
177      * with the specified buffer size.
178      *
179      * @param   file    the file
180      * @param   size   the buffer size.
181      * @exception IllegalArgumentException if size <= 0.
182      */
183     public SharedFileInputStream(String   file, int size) throws IOException {
184     super(null);    // XXX - will it NPE?
185         if (size <= 0)
186             throw new IllegalArgumentException  ("Buffer size <= 0");
187     init(new SharedFile(file), size);
188     }
189 
190     private void init(SharedFile sf, int size) throws IOException {
191     this.sf = sf;
192     this.in = sf.open();
193     this.start = 0;
194     this.datalen = in.length(); // XXX - file can't grow
195     this.bufsize = size;
196     buf = new byte[size];
197     }
198 
199     /**
200      * Used internally by the <code>newStream</code> method.
201      */
202     private SharedFileInputStream(SharedFile sf, long start, long len,
203                 int bufsize) {
204     super(null);
205     this.master = false;
206     this.sf = sf;
207     this.in = sf.open();
208     this.start = start;
209     this.bufpos = start;
210     this.datalen = len;
211     this.bufsize = bufsize;
212     buf = new byte[bufsize];
213     }
214 
215     /**
216      * Fills the buffer with more data, taking into account
217      * shuffling and other tricks for dealing with marks.
218      * Assumes that it is being called by a synchronized method.
219      * This method also assumes that all data has already been read in,
220      * hence pos > count.
221      */
222     private void fill() throws IOException {
223     if (markpos < 0) {
224         pos = 0;        /* no mark: throw away the buffer */
225         bufpos += count;
226     } else if (pos >= buf.length)   /* no room left in buffer */
227         if (markpos > 0) {  /* can throw away early part of the buffer */
228         int sz = pos - markpos;
229         System.arraycopy(buf, markpos, buf, 0, sz);
230         pos = sz;
231         bufpos += markpos;
232         markpos = 0;
233         } else if (buf.length >= marklimit) {
234         markpos = -1;   /* buffer got too big, invalidate mark */
235         pos = 0;    /* drop buffer contents */
236         bufpos += count;
237         } else {        /* grow buffer */
238         int nsz = pos * 2;
239         if (nsz > marklimit)
240             nsz = marklimit;
241         byte nbuf[] = new byte[nsz];
242         System.arraycopy(buf, 0, nbuf, 0, pos);
243         buf = nbuf;
244         }
245         count = pos;
246     in.seek(bufpos + pos);
247     // limit to datalen
248     int len = buf.length - pos;
249     if (bufpos - start + pos + len > datalen)
250         len = (int)(datalen - (bufpos - start + pos));
251     int n = in.read(buf, pos, len);
252         if (n > 0)
253             count = n + pos;
254     }
255 
256     /**
257      * See the general contract of the <code>read</code>
258      * method of <code>InputStream</code>.
259      *
260      * @return     the next byte of data, or <code>-1</code> if the end of the
261      *             stream is reached.
262      * @exception  IOException  if an I/O error occurs.
263      */
264     public synchronized int read() throws IOException {
265         ensureOpen();
266     if (pos >= count) {
267         fill();
268         if (pos >= count)
269         return -1;
270     }
271     return buf[pos++] & 0xff;
272     }
273 
274     /**
275      * Read characters into a portion of an array, reading from the underlying
276      * stream at most once if necessary.
277      */
278     private int read1(byte[] b, int off, int len) throws IOException {
279     int avail = count - pos;
280     if (avail <= 0) {
281         if (false) {
282         /* If the requested length is at least as large as the buffer, and
283            if there is no mark/reset activity, do not bother to copy the
284            bytes into the local buffer.  In this way buffered streams will
285            cascade harmlessly. */
286         if (len >= buf.length && markpos < 0) {
287         // XXX - seek, update bufpos - how?
288         return in.read(b, off, len);
289         }
290         }
291         fill();
292         avail = count - pos;
293         if (avail <= 0) return -1;
294     }
295     int cnt = (avail < len) ? avail : len;
296     System.arraycopy(buf, pos, b, off, cnt);
297     pos += cnt;
298     return cnt;
299     }
300 
301     /**
302      * Reads bytes from this stream into the specified byte array,
303      * starting at the given offset.
304      *
305      * <p> This method implements the general contract of the corresponding
306      * <code>{@link java.io.InputStream#read(byte[], int, int) read}</code>
307      * method of the <code>{@link java.io.InputStream}</code> class.
308      *
309      * @param      b     destination buffer.
310      * @param      off   offset at which to start storing bytes.
311      * @param      len   maximum number of bytes to read.
312      * @return     the number of bytes read, or <code>-1</code> if the end of
313      *             the stream has been reached.
314      * @exception  IOException  if an I/O error occurs.
315      */
316     public synchronized int read(byte b[], int off, int len)
317     throws IOException
318     {
319         ensureOpen();
320         if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
321         throw new IndexOutOfBoundsException  ();
322     } else if (len == 0) {
323         return 0;
324     }
325 
326     int n = read1(b, off, len);
327     if (n <= 0) return n;
328     while ((n < len) /* && (in.available() > 0) */) {
329         int n1 = read1(b, off + n, len - n);
330         if (n1 <= 0) break;
331         n += n1;
332     }
333     return n;
334     }
335 
336     /**
337      * See the general contract of the <code>skip</code>
338      * method of <code>InputStream</code>.
339      *
340      * @param      n   the number of bytes to be skipped.
341      * @return     the actual number of bytes skipped.
342      * @exception  IOException  if an I/O error occurs.
343      */
344     public synchronized long skip(long n) throws IOException {
345         ensureOpen();
346     if (n <= 0) {
347         return 0;
348     }
349     long avail = count - pos;
350      
351         if (avail <= 0) {
352             // If no mark position set then don't keep in buffer
353         /*
354             if (markpos <0) 
355                 return in.skip(n);
356         */
357             
358             // Fill in buffer to save bytes for reset
359             fill();
360             avail = count - pos;
361             if (avail <= 0)
362                 return 0;
363         }
364         
365         long skipped = (avail < n) ? avail : n;
366         pos += skipped;
367         return skipped;
368     }
369 
370     /**
371      * Returns the number of bytes that can be read from this input 
372      * stream without blocking. 
373      *
374      * @return     the number of bytes that can be read from this input
375      *             stream without blocking.
376      * @exception  IOException  if an I/O error occurs.
377      */
378     public synchronized int available() throws IOException {
379         ensureOpen();
380     return (count - pos) + in_available();
381     }
382 
383     private int in_available() throws IOException {
384     // XXX - overflow
385     return (int)((start + datalen) - (bufpos + count));
386     }
387 
388     /** 
389      * See the general contract of the <code>mark</code>
390      * method of <code>InputStream</code>.
391      *
392      * @param   readlimit   the maximum limit of bytes that can be read before
393      *                      the mark position becomes invalid.
394      * @see     #reset()
395      */
396     public synchronized void mark(int readlimit) {
397     marklimit = readlimit;
398     markpos = pos;
399     }
400 
401     /**
402      * See the general contract of the <code>reset</code>
403      * method of <code>InputStream</code>.
404      * <p>
405      * If <code>markpos</code> is <code>-1</code>
406      * (no mark has been set or the mark has been
407      * invalidated), an <code>IOException</code>
408      * is thrown. Otherwise, <code>pos</code> is
409      * set equal to <code>markpos</code>.
410      *
411      * @exception  IOException  if this stream has not been marked or
412      *               if the mark has been invalidated.
413      * @see        #mark(int)
414      */
415     public synchronized void reset() throws IOException {
416         ensureOpen();
417     if (markpos < 0)
418         throw new IOException("Resetting to invalid mark");
419     pos = markpos;
420     }
421 
422     /**
423      * Tests if this input stream supports the <code>mark</code> 
424      * and <code>reset</code> methods. The <code>markSupported</code> 
425      * method of <code>SharedFileInputStream</code> returns 
426      * <code>true</code>. 
427      *
428      * @return  a <code>boolean</code> indicating if this stream type supports
429      *          the <code>mark</code> and <code>reset</code> methods.
430      * @see     java.io.InputStream#mark(int)
431      * @see     java.io.InputStream#reset()
432      */
433     public boolean markSupported() {
434     return true;
435     }
436 
437     /**
438      * Closes this input stream and releases any system resources 
439      * associated with the stream. 
440      *
441      * @exception  IOException  if an I/O error occurs.
442      */
443     public void close() throws IOException {
444         if (in == null)
445             return;
446     try {
447         if (master)
448         sf.forceClose();
449         else
450         sf.close();
451     } finally {
452         sf = null;
453         in = null;
454         buf = null;
455     }
456     }
457 
458     /**
459      * Return the current position in the InputStream, as an
460      * offset from the beginning of the InputStream.
461      *
462      * @return  the current position
463      */
464     public long getPosition() {
465 //System.out.println("getPosition: start " + start + " pos " + pos + " bufpos " + bufpos + " = " + (bufpos + pos - start));
466     if (in == null)
467         throw new RuntimeException  ("Stream closed");
468     return bufpos + pos - start;
469     }
470 
471     /**
472      * Return a new InputStream representing a subset of the data
473      * from this InputStream, starting at <code>start</code> (inclusive)
474      * up to <code>end</code> (exclusive).  <code>start</code> must be
475      * non-negative.  If <code>end</code> is -1, the new stream ends
476      * at the same place as this stream.  The returned InputStream
477      * will also implement the SharedInputStream interface.
478      *
479      * @param   start   the starting position
480      * @param   end the ending position + 1
481      * @return      the new stream
482      */
483     public InputStream   newStream(long start, long end) {
484     if (in == null)
485         throw new RuntimeException  ("Stream closed");
486     if (start < 0)
487         throw new IllegalArgumentException  ("start < 0");
488     if (end == -1)
489         end = datalen;
490     return new SharedFileInputStream(sf,
491             this.start + (int)start, (int)(end - start), bufsize);
492     }
493 
494     // for testing...
495     /*
496     public static void main(String[] argv) throws Exception {
497     SharedFileInputStream is = new SharedFileInputStream(argv[0]);
498     java.util.Random r = new java.util.Random();
499     int b;
500     while ((b = is.read()) >= 0) {
501         System.out.write(b);
502         if (r.nextDouble() < 0.3) {
503         InputStream is2 = is.newStream(is.getPosition(), -1);
504         int b2;
505         while ((b2 = is2.read()) >= 0)
506             ;
507         }
508     }
509     }
510     */
511 
512     /**
513      * Force this stream to close.
514      */
515     protected void finalize() throws Throwable   {
516     super.finalize();
517     close();
518     }
519 }
520
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