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Java > Open Source Codes > org > eclipse > core > internal > runtime > SafeFileOutputStream


1 /*******************************************************************************
2  * Copyright (c) 2000, 2004 IBM Corporation and others.
3  * All rights reserved. This program and the accompanying materials
4  * are made available under the terms of the Common Public License v1.0
5  * which accompanies this distribution, and is available at
6  * http://www.eclipse.org/legal/cpl-v10.html
7  *
8  * Contributors:
9  * IBM Corporation - initial API and implementation
10  *******************************************************************************/
11 package org.eclipse.core.internal.runtime;
12
13 import java.io.*;
14
15 /**
16  * This class should be used when there's a file already in the
17  * destination and we don't want to lose its contents if a
18  * failure writing this stream happens.
19  * Basically, the new contents are written to a temporary location.
20  * If everything goes OK, it is moved to the right place.
21  * The user has the option to define the temporary location or
22  * it will be created in the default-temporary directory
23  * (see java.io.File for details).
24  */
25 public class SafeFileOutputStream extends OutputStream {
26     protected File temp;
27     protected File target;
28     protected OutputStream output;
29     protected boolean failed;
30     protected static final String JavaDoc EXTENSION = ".bak"; //$NON-NLS-1$
31
32     public SafeFileOutputStream(File file) throws IOException {
33         this(file.getAbsolutePath(), null);
34     }
35
36     public SafeFileOutputStream(String JavaDoc targetName) throws IOException {
37         this(targetName, null);
38     }
39
40     /**
41      * If targetPath is null, the file will be created in the default-temporary directory.
42      */
43     public SafeFileOutputStream(String JavaDoc targetPath, String JavaDoc tempPath) throws IOException {
44         failed = false;
45         target = new File(targetPath);
46         createTempFile(tempPath);
47         // If we do not have a file at target location, but we do have at temp location,
48 // it probably means something wrong happened the last time we tried to write it.
49 // So, try to recover the backup file. And, if successful, write the new one.
50 if (!target.exists() && !temp.exists()) {
51             output = new BufferedOutputStream(new FileOutputStream(target));
52             return;
53         }
54         copy(temp, target);
55         output = new BufferedOutputStream(new FileOutputStream(temp));
56     }
57
58     public void close() throws IOException {
59         close(false);
60     }
61     
62     public void close(boolean discard) throws IOException {
63         try {
64             output.close();
65         } catch (IOException e) {
66             failed = true;
67             throw e; // rethrow
68 }
69         if (discard || failed)
70             temp.delete();
71         else
72             commit();
73     }
74
75     protected void commit() throws IOException {
76         if (!temp.exists())
77             return;
78         target.delete();
79         copy(temp, target);
80         temp.delete();
81     }
82
83     protected void copy(File sourceFile, File destinationFile) throws IOException {
84         if (!sourceFile.exists())
85             return;
86         if (sourceFile.renameTo(destinationFile))
87             return;
88         InputStream source = new BufferedInputStream(new FileInputStream(sourceFile));
89         OutputStream destination = new BufferedOutputStream(new FileOutputStream(destinationFile));
90         transferStreams(source, destination);
91     }
92
93     protected void createTempFile(String JavaDoc tempPath) {
94         if (tempPath == null)
95             tempPath = target.getAbsolutePath() + EXTENSION;
96         temp = new File(tempPath);
97     }
98     
99     public void flush() throws IOException {
100         try {
101             output.flush();
102         } catch (IOException e) {
103             failed = true;
104             throw e; // rethrow
105 }
106     }
107
108     public String JavaDoc getTempFilePath() {
109         return temp.getAbsolutePath();
110     }
111
112     protected void transferStreams(InputStream source, OutputStream destination) throws IOException {
113         try {
114             byte[] buffer = new byte[8192];
115             while (true) {
116                 int bytesRead = source.read(buffer);
117                 if (bytesRead == -1)
118                     break;
119                 destination.write(buffer, 0, bytesRead);
120             }
121         } finally {
122             try {
123                 source.close();
124             } catch (IOException e) {
125                 // do nothing
126 }
127             try {
128                 destination.close();
129             } catch (IOException e) {
130                 // do nothing
131 }
132         }
133     }
134
135     public void write(int b) throws IOException {
136         try {
137             output.write(b);
138         } catch (IOException e) {
139             failed = true;
140             throw e; // rethrow
141 }
142     }
143 }
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