FileBackupHelper.java revision 4528186e0d65fc68ef0dd1941aa2ac8aefcd55a3 
1/*
2 * Copyright (C) 2009 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.app.backup;
18
19import android.content.Context;
20import android.os.ParcelFileDescriptor;
21import android.util.Log;
22
23import java.io.File;
24
25/**
26 * A helper class which can be used in conjunction with
27 * {@link android.app.backup.BackupHelperAgent} to manage the backup of a set of
28 * files. Whenever backup is performed, all files changed since the last backup
29 * will be saved in their entirety. During the first time the backup happens,
30 * all the files in the list will be backed up. Note that this should only be
31 * used with small configuration files and not with large binary files.
32 * <p>
33 * Any files not present in the list of files during the restore procedure will
34 * be ignored. If files present in a previous version of an application are
35 * removed in subsequent versions, it is the responsibility of the developer to
36 * design a mechanism to remove those files. Otherwise files no longer needed
37 * will linger and consume space on the device.
38 * <p>
39 * STOPSHIP: document! [manages backup of a set of files; restore is totally
40 * opaque]
41 */
42public class FileBackupHelper extends FileBackupHelperBase implements BackupHelper {
43    private static final String TAG = "FileBackupHelper";
44    private static final boolean DEBUG = false;
45
46    Context mContext;
47    File mFilesDir;
48    String[] mFiles;
49
50    /**
51     * Construct a helper to manage backup/restore of entire files within the
52     * application's data directory hierarchy.
53     *
54     * @param context The backup agent's Context object
55     * @param files A list of the files to be backed up or restored.
56     */
57    public FileBackupHelper(Context context, String... files) {
58        super(context);
59
60        mContext = context;
61        mFilesDir = context.getFilesDir();
62        mFiles = files;
63    }
64
65    /**
66     * Based on <code>oldState</code>, determine which of the files from the
67     * application's data directory need to be backed up, write them to the data
68     * stream, and fill in <code>newState</code> with the state as it exists
69     * now. When <code>oldState</code> is <code>null</code>, all the files will
70     * be backed up.
71     * <p>
72     * This should be called from {@link android.app.backup.BackupHelperAgent}
73     * directly. See
74     * {@link android.app.backup.BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor)}
75     * for a description of parameter meanings.
76     */
77    public void performBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
78            ParcelFileDescriptor newState) {
79        // file names
80        String[] files = mFiles;
81        File base = mContext.getFilesDir();
82        final int N = files.length;
83        String[] fullPaths = new String[N];
84        for (int i=0; i<N; i++) {
85            fullPaths[i] = (new File(base, files[i])).getAbsolutePath();
86        }
87
88        // go
89        performBackup_checked(oldState, data, newState, fullPaths, files);
90    }
91
92    /**
93     * Restore one record [representing a single file] from the restore dataset.
94     */
95    public void restoreEntity(BackupDataInputStream data) {
96        if (DEBUG) Log.d(TAG, "got entity '" + data.getKey() + "' size=" + data.size());
97        String key = data.getKey();
98        if (isKeyInList(key, mFiles)) {
99            File f = new File(mFilesDir, key);
100            writeFile(f, data);
101        }
102    }
103}
104
105