Home | History | Annotate | Download | only in backuprestore 
      1 /*
      2  * Copyright (C) 2010 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 
     17 package com.example.android.backuprestore;
     18 
     19 import java.io.ByteArrayOutputStream;
     20 import java.io.ByteArrayInputStream;
     21 import java.io.DataInputStream;
     22 import java.io.DataOutputStream;
     23 import java.io.File;
     24 import java.io.FileInputStream;
     25 import java.io.FileOutputStream;
     26 import java.io.IOException;
     27 import java.io.RandomAccessFile;
     28 
     29 import android.app.backup.BackupAgent;
     30 import android.app.backup.BackupDataInput;
     31 import android.app.backup.BackupDataOutput;
     32 import android.os.ParcelFileDescriptor;
     33 
     34 /**
     35  * This agent implementation is similar to the {@link ExampleAgent} one, but
     36  * stores each distinct piece of application data in a separate record within
     37  * the backup data set.  These records are updated independently: if the user
     38  * changes the state of one of the UI's checkboxes, for example, only that
     39  * datum's backup record is updated, not the entire data file.
     40  */
     41 public class MultiRecordExampleAgent extends BackupAgent {
     42     // Key strings for each record in the backup set
     43     static final String FILLING_KEY = "filling";
     44     static final String MAYO_KEY = "mayo";
     45     static final String TOMATO_KEY = "tomato";
     46 
     47     // Current live data, read from the application's data file
     48     int mFilling;
     49     boolean mAddMayo;
     50     boolean mAddTomato;
     51 
     52     /** The location of the application's persistent data file */
     53     File mDataFile;
     54 
     55     @Override
     56     public void onCreate() {
     57         // Cache a File for the app's data
     58         mDataFile = new File(getFilesDir(), BackupRestoreActivity.DATA_FILE_NAME);
     59     }
     60 
     61     @Override
     62     public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
     63             ParcelFileDescriptor newState) throws IOException {
     64         // First, get the current data from the application's file.  This
     65         // may throw an IOException, but in that case something has gone
     66         // badly wrong with the app's data on disk, and we do not want
     67         // to back up garbage data.  If we just let the exception go, the
     68         // Backup Manager will handle it and simply skip the current
     69         // backup operation.
     70         synchronized (BackupRestoreActivity.sDataLock) {
     71             RandomAccessFile file = new RandomAccessFile(mDataFile, "r");
     72             mFilling = file.readInt();
     73             mAddMayo = file.readBoolean();
     74             mAddTomato = file.readBoolean();
     75         }
     76 
     77         // If this is the first backup ever, we have to back up everything
     78         boolean forceBackup = (oldState == null);
     79 
     80         // Now read the state as of the previous backup pass, if any
     81         int lastFilling = 0;
     82         boolean lastMayo = false;
     83         boolean lastTomato = false;
     84 
     85         if (!forceBackup) {
     86 
     87             FileInputStream instream = new FileInputStream(oldState.getFileDescriptor());
     88             DataInputStream in = new DataInputStream(instream);
     89 
     90             try {
     91                 // Read the state as of the last backup
     92                 lastFilling = in.readInt();
     93                 lastMayo = in.readBoolean();
     94                 lastTomato = in.readBoolean();
     95             } catch (IOException e) {
     96                 // If something went wrong reading the state file, be safe and
     97                 // force a backup of all the data again.
     98                 forceBackup = true;
     99             }
    100         }
    101 
    102         // Okay, now check each datum to see whether we need to back up a new value.  We'll
    103         // reuse the bytearray buffering stream for each datum.  We also use a little
    104         // helper routine to avoid some code duplication when writing the two boolean
    105         // records.
    106         ByteArrayOutputStream bufStream = new ByteArrayOutputStream();
    107         DataOutputStream out = new DataOutputStream(bufStream);
    108 
    109         if (forceBackup || (mFilling != lastFilling)) {
    110             // bufStream.reset();   // not necessary the first time, but good to remember
    111             out.writeInt(mFilling);
    112             writeBackupEntity(data, bufStream, FILLING_KEY);
    113         }
    114 
    115         if (forceBackup || (mAddMayo != lastMayo)) {
    116             bufStream.reset();
    117             out.writeBoolean(mAddMayo);
    118             writeBackupEntity(data, bufStream, MAYO_KEY);
    119         }
    120 
    121         if (forceBackup || (mAddTomato != lastTomato)) {
    122             bufStream.reset();
    123             out.writeBoolean(mAddTomato);
    124             writeBackupEntity(data, bufStream, TOMATO_KEY);
    125         }
    126 
    127         // Finally, write the state file that describes our data as of this backup pass
    128         writeStateFile(newState);
    129     }
    130 
    131     /**
    132      * Write out the new state file:  the version number, followed by the
    133      * three bits of data as we sent them off to the backup transport.
    134      */
    135     void writeStateFile(ParcelFileDescriptor stateFile) throws IOException {
    136         FileOutputStream outstream = new FileOutputStream(stateFile.getFileDescriptor());
    137         DataOutputStream out = new DataOutputStream(outstream);
    138 
    139         out.writeInt(mFilling);
    140         out.writeBoolean(mAddMayo);
    141         out.writeBoolean(mAddTomato);
    142     }
    143 
    144     // Helper: write the boolean 'value' as a backup record under the given 'key',
    145     // reusing the given buffering stream & data writer objects to do so.
    146     void writeBackupEntity(BackupDataOutput data, ByteArrayOutputStream bufStream, String key)
    147             throws IOException {
    148         byte[] buf = bufStream.toByteArray();
    149         data.writeEntityHeader(key, buf.length);
    150         data.writeEntityData(buf, buf.length);
    151     }
    152 
    153     /**
    154      * On restore, we pull the various bits of data out of the restore stream,
    155      * then reconstruct the application's data file inside the shared lock.  A
    156      * restore data set will always be the full set of records supplied by the
    157      * application's backup operations.
    158      */
    159     @Override
    160     public void onRestore(BackupDataInput data, int appVersionCode,
    161             ParcelFileDescriptor newState) throws IOException {
    162 
    163         // Consume the restore data set, remembering each bit of application state
    164         // that we see along the way
    165         while (data.readNextHeader()) {
    166             String key = data.getKey();
    167             int dataSize = data.getDataSize();
    168 
    169             // In this implementation, we trust that we won't see any record keys
    170             // that we don't understand.  Since we expect to handle them all, we
    171             // go ahead and extract the data for each record before deciding how
    172             // it will be handled.
    173             byte[] dataBuf = new byte[dataSize];
    174             data.readEntityData(dataBuf, 0, dataSize);
    175             ByteArrayInputStream instream = new ByteArrayInputStream(dataBuf);
    176             DataInputStream in = new DataInputStream(instream);
    177 
    178             if (FILLING_KEY.equals(key)) {
    179                 mFilling = in.readInt();
    180             } else if (MAYO_KEY.equals(key)) {
    181                 mAddMayo = in.readBoolean();
    182             } else if (TOMATO_KEY.equals(key)) {
    183                 mAddTomato = in.readBoolean();
    184             }
    185         }
    186 
    187         // Now we're ready to write out a full new dataset for the application.  Note that
    188         // the restore process is intended to *replace* any existing or default data, so
    189         // we can just go ahead and overwrite it all.
    190         synchronized (BackupRestoreActivity.sDataLock) {
    191             RandomAccessFile file = new RandomAccessFile(mDataFile, "rw");
    192             file.setLength(0L);
    193             file.writeInt(mFilling);
    194             file.writeBoolean(mAddMayo);
    195             file.writeBoolean(mAddTomato);
    196         }
    197 
    198         // Finally, write the state file that describes our data as of this restore pass.
    199         writeStateFile(newState);
    200     }
    201 }
    202