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      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 
     17 package com.android.internal.util;
     18 
     19 import java.io.File;
     20 import java.io.IOException;
     21 
     22 /**
     23  * @deprecated Use {@link com.android.internal.os.AtomicFile} instead.  It would
     24  * be nice to update all existing uses of this to switch to AtomicFile, but since
     25  * their on-file semantics are slightly different that would run the risk of losing
     26  * data if at the point of the platform upgrade to the new code it would need to
     27  * roll back to the backup file.  This can be solved...  but is it worth it and
     28  * all of the testing needed to make sure it is correct?
     29  */
     30 @Deprecated
     31 public class JournaledFile {
     32     File mReal;
     33     File mTemp;
     34     boolean mWriting;
     35 
     36     public JournaledFile(File real, File temp) {
     37         mReal = real;
     38         mTemp = temp;
     39     }
     40 
     41     /** Returns the file for you to read.
     42      * @more
     43      * Prefers the real file.  If it doesn't exist, uses the temp one, and then copies
     44      * it to the real one.  If there is both a real file and a temp one, assumes that the
     45      * temp one isn't fully written and deletes it.
     46      */
     47     public File chooseForRead() {
     48         File result;
     49         if (mReal.exists()) {
     50             result = mReal;
     51             if (mTemp.exists()) {
     52                 mTemp.delete();
     53             }
     54         } else if (mTemp.exists()) {
     55             result = mTemp;
     56             mTemp.renameTo(mReal);
     57         } else {
     58             return mReal;
     59         }
     60         return result;
     61     }
     62 
     63     /**
     64      * Returns a file for you to write.
     65      * @more
     66      * If a write is already happening, throws.  In other words, you must provide your
     67      * own locking.
     68      * <p>
     69      * Call {@link #commit} to commit the changes, or {@link #rollback} to forget the changes.
     70      */
     71     public File chooseForWrite() {
     72         if (mWriting) {
     73             throw new IllegalStateException("uncommitted write already in progress");
     74         }
     75         if (!mReal.exists()) {
     76             // If the real one doesn't exist, it's either because this is the first time
     77             // or because something went wrong while copying them.  In this case, we can't
     78             // trust anything that's in temp.  In order to have the chooseForRead code not
     79             // use the temporary one until it's fully written, create an empty file
     80             // for real, which will we'll shortly delete.
     81             try {
     82                 mReal.createNewFile();
     83             } catch (IOException e) {
     84                 // Ignore
     85             }
     86         }
     87 
     88         if (mTemp.exists()) {
     89             mTemp.delete();
     90         }
     91         mWriting = true;
     92         return mTemp;
     93     }
     94 
     95     /**
     96      * Commit changes.
     97      */
     98     public void commit() {
     99         if (!mWriting) {
    100             throw new IllegalStateException("no file to commit");
    101         }
    102         mWriting = false;
    103         mTemp.renameTo(mReal);
    104     }
    105 
    106     /**
    107      * Roll back changes.
    108      */
    109     public void rollback() {
    110         if (!mWriting) {
    111             throw new IllegalStateException("no file to roll back");
    112         }
    113         mWriting = false;
    114         mTemp.delete();
    115     }
    116 }
    117