AtomicFileWriter


1   package hudson.util;
2   
3   import java.io.BufferedWriter  ;
4   import java.io.File  ;
5   import java.io.FileOutputStream  ;
6   import java.io.FileWriter  ;
7   import java.io.IOException  ;
8   import java.io.OutputStreamWriter  ;
9   import java.io.Writer  ;
10  
11  /**
12   * Buffered {@link FileWriter} that uses UTF-8.
13   *
14   * <p>
15   * The write operation is atomic when used for overwriting;
16   * it either leaves the original file intact, or it completely rewrites it with new contents.
17   *
18   * @author Kohsuke Kawaguchi
19   */
20  public class AtomicFileWriter extends Writer   {
21  
22      private final Writer   core;
23      private final File   tmpFile;
24      private final File   destFile;
25  
26      public AtomicFileWriter(File   f) throws IOException   {
27          tmpFile = File.createTempFile("atomic",null,f.getParentFile());
28          destFile = f;
29          core = new BufferedWriter  (new OutputStreamWriter  (new FileOutputStream  (tmpFile),"UTF-8"));
30      }
31  
32      public void write(int c) throws IOException   {
33          core.write(c);
34      }
35  
36      public void write(String   str, int off, int len) throws IOException   {
37          core.write(str,off,len);
38      }
39  
40      public void write(char cbuf[], int off, int len) throws IOException   {
41          core.write(cbuf,off,len);
42      }
43  
44      public void flush() throws IOException   {
45          core.flush();
46      }
47  
48      public void close() throws IOException   {
49          core.close();
50      }
51  
52      public void commit() throws IOException   {
53          close();
54          if(destFile.exists() && !destFile.delete())
55              throw new IOException  ("Unable to delete "+destFile);
56          tmpFile.renameTo(destFile);
57      }
58  }
59
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