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Java > Open Source Codes > persistence > antlr > PreservingFileWriter


1 package persistence.antlr;
2
3 /* ANTLR Translator Generator
4  * Project led by Terence Parr at http://www.jGuru.com
5  * Software rights: http://www.antlr.org/license.html
6  *
7  * @author Ric Klaren <klaren@cs.utwente.nl>
8  */
9
10 import java.io.*;
11
12 /** PreservingFileWriter only overwrites target if the new file is different.
13  Mainly added in order to prevent big and unnecessary recompiles in C++
14  projects.
15  I/O is buffered.
16 */
17 public class PreservingFileWriter extends FileWriter {
18     protected File target_file; /// the file we intend to write to
19 protected File tmp_file; /// the tmp file we create at first
20
21     public PreservingFileWriter(String JavaDoc file) throws IOException
22     {
23         super(file+".antlr.tmp");
24
25         // set up File thingy for target..
26 target_file = new File(file);
27
28         String JavaDoc parentdirname = target_file.getParent();
29         if( parentdirname != null )
30         {
31             File parentdir = new File(parentdirname);
32
33             if (!parentdir.exists())
34                 throw new IOException("destination directory of '"+file+"' doesn't exist");
35             if (!parentdir.canWrite())
36                 throw new IOException("destination directory of '"+file+"' isn't writeable");
37         }
38         if( target_file.exists() && ! target_file.canWrite() )
39             throw new IOException("cannot write to '"+file+"'");
40
41         // and for the temp file
42 tmp_file = new File(file+".antlr.tmp");
43         // have it nuked at exit
44 // RK: this is broken on java 1.4 and
45 // is not compatible with java 1.1 (which is a big problem I'm told :) )
46 // sigh. Any real language would do this in a destructor ;) ;)
47 // tmp_file.deleteOnExit();
48 }
49
50     /** Close the file and see if the actual target is different
51      * if so the target file is overwritten by the copy. If not we do nothing
52      */
53     public void close() throws IOException
54     {
55         Reader source = null;
56         Writer target = null;
57
58         try {
59             // close the tmp file so we can access it safely...
60 super.close();
61
62             char[] buffer = new char[1024];
63             int cnt;
64
65             // target_file != tmp_file so we have to compare and move it..
66 if( target_file.length() == tmp_file.length() )
67             {
68                 // Do expensive read'n'compare
69 Reader tmp;
70                 char[] buf2 = new char[1024];
71
72                 source = new BufferedReader(new FileReader(tmp_file));
73                 tmp = new BufferedReader(new FileReader(target_file));
74                 int cnt1, cnt2;
75                 boolean equal = true;
76
77                 while( equal )
78                 {
79                     cnt1 = source.read(buffer,0,1024);
80                     cnt2 = tmp.read(buf2,0,1024);
81                     if( cnt1 != cnt2 )
82                     {
83                         equal = false;
84                         break;
85                     }
86                     if( cnt1 == -1 ) // EOF
87 break;
88                     for( int i = 0; i < cnt1; i++ )
89                     {
90                         if( buffer[i] != buf2[i] )
91                         {
92                             equal = false;
93                             break;
94                         }
95                     }
96                 }
97                 // clean up...
98 source.close();
99                 tmp.close();
100
101                 source = tmp = null;
102
103                 if( equal )
104                     return;
105             }
106
107             source = new BufferedReader(new FileReader(tmp_file));
108             target = new BufferedWriter(new FileWriter(target_file));
109
110             while(true)
111             {
112                 cnt = source.read(buffer,0,1024);
113                 if( cnt == -1 )
114                     break;
115                 target.write(buffer, 0, cnt );
116             }
117         }
118         finally {
119             if( source != null )
120             {
121                 try { source.close(); }
122                 catch( IOException e ) { ; }
123             }
124             if( target != null )
125             {
126                 try { target.close(); }
127                 catch( IOException e ) { ; }
128             }
129             // RK: Now if I'm correct this should be called anytime.
130 if( tmp_file != null && tmp_file.exists() )
131             {
132                 tmp_file.delete();
133                 tmp_file = null;
134             }
135         }
136     }
137 }
138
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