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


1 /*******************************************************************************
2  * Copyright (c) 2000, 2005 IBM Corporation and others.
3  * All rights reserved. This program and the accompanying materials
4  * are made available under the terms of the Eclipse Public License v1.0
5  * which accompanies this distribution, and is available at
6  * http://www.eclipse.org/legal/epl-v10.html
7  *
8  * Contributors:
9  * IBM Corporation - initial API and implementation
10  *******************************************************************************/
11 package org.eclipse.core.internal.localstore;
12
13 import java.io.*;
14 import org.eclipse.core.internal.utils.FileUtil;
15
16 /**
17  * This class should be used when there's a file already in the
18  * destination and we don't want to lose its contents if a
19  * failure writing this stream happens.
20  * Basically, the new contents are written to a temporary location.
21  * If everything goes OK, it is moved to the right place.
22  * The user has the option to define the temporary location or
23  * it will be created in the default-temporary directory
24  * (see java.io.File for details).
25  */
26 public class SafeFileOutputStream extends OutputStream {
27     protected File temp;
28     protected File target;
29     protected OutputStream output;
30     protected boolean failed;
31     protected static final String JavaDoc EXTENSION = ".bak"; //$NON-NLS-1$
32
33     public SafeFileOutputStream(File file) throws IOException {
34         this(file.getAbsolutePath(), null);
35     }
36
37     /**
38      * If targetPath is null, the file will be created in the default-temporary directory.
39      */
40     public SafeFileOutputStream(String JavaDoc targetPath, String JavaDoc tempPath) throws IOException {
41         failed = false;
42         target = new File(targetPath);
43         createTempFile(tempPath);
44         if (!target.exists()) {
45             if (!temp.exists()) {
46                 output = new BufferedOutputStream(new FileOutputStream(target));
47                 return;
48             }
49             // If we do not have a file at target location, but we do have at temp location,
50 // it probably means something wrong happened the last time we tried to write it.
51 // So, try to recover the backup file. And, if successful, write the new one.
52 copy(temp, target);
53         }
54         output = new BufferedOutputStream(new FileOutputStream(temp));
55     }
56
57     public void close() throws IOException {
58         try {
59             output.close();
60         } catch (IOException e) {
61             failed = true;
62             throw e; // rethrow
63 }
64         if (failed)
65             temp.delete();
66         else
67             commit();
68     }
69
70     protected void commit() throws IOException {
71         if (!temp.exists())
72             return;
73         target.delete();
74         copy(temp, target);
75         temp.delete();
76     }
77
78     protected void copy(File sourceFile, File destinationFile) throws IOException {
79         if (!sourceFile.exists())
80             return;
81         if (sourceFile.renameTo(destinationFile))
82             return;
83         InputStream source = null;
84         OutputStream destination = null;
85         try {
86             source = new BufferedInputStream(new FileInputStream(sourceFile));
87             destination = new BufferedOutputStream(new FileOutputStream(destinationFile));
88             transferStreams(source, destination);
89         } finally {
90             FileUtil.safeClose(source);
91             FileUtil.safeClose(destination);
92         }
93     }
94
95     protected void createTempFile(String JavaDoc tempPath) {
96         if (tempPath == null)
97             tempPath = target.getAbsolutePath() + EXTENSION;
98         temp = new File(tempPath);
99     }
100
101     public void flush() throws IOException {
102         try {
103             output.flush();
104         } catch (IOException e) {
105             failed = true;
106             throw e; // rethrow
107 }
108     }
109
110     public String JavaDoc getTempFilePath() {
111         return temp.getAbsolutePath();
112     }
113
114     protected void transferStreams(InputStream source, OutputStream destination) throws IOException {
115         byte[] buffer = new byte[8192];
116         while (true) {
117             int bytesRead = source.read(buffer);
118             if (bytesRead == -1)
119                 break;
120             destination.write(buffer, 0, bytesRead);
121         }
122     }
123
124     public void write(int b) throws IOException {
125         try {
126             output.write(b);
127         } catch (IOException e) {
128             failed = true;
129             throw e; // rethrow
130 }
131     }
132 }
133
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