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Android example source code file (AtomicFile.java)

This example Android source code file (AtomicFile.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

android, atomicfile, couldn't, fileinputstream, filenotfoundexception, fileoutputstream, got, io, ioexception, os, util, utilities, utils

The AtomicFile.java Android example source code

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.internal.os;

import android.os.FileUtils;
import android.util.Log;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

/**
 * Helper class for performing atomic operations on a file, by creating a
 * backup file until a write has successfully completed.
 */
public class AtomicFile {
    private final File mBaseName;
    private final File mBackupName;
    
    public AtomicFile(File baseName) {
        mBaseName = baseName;
        mBackupName = new File(baseName.getPath() + ".bak");
    }
    
    public File getBaseFile() {
        return mBaseName;
    }
    
    public FileOutputStream startWrite() throws IOException {
        // Rename the current file so it may be used as a backup during the next read
        if (mBaseName.exists()) {
            if (!mBackupName.exists()) {
                if (!mBaseName.renameTo(mBackupName)) {
                    Log.w("AtomicFile", "Couldn't rename file " + mBaseName
                            + " to backup file " + mBackupName);
                }
            } else {
                mBaseName.delete();
            }
        }
        FileOutputStream str = null;
        try {
            str = new FileOutputStream(mBaseName);
        } catch (FileNotFoundException e) {
            File parent = mBaseName.getParentFile();
            if (!parent.mkdir()) {
                throw new IOException("Couldn't create directory " + mBaseName);
            }
            FileUtils.setPermissions(
                parent.getPath(),
                FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH,
                -1, -1);
            try {
                str = new FileOutputStream(mBaseName);
            } catch (FileNotFoundException e2) {
                throw new IOException("Couldn't create " + mBaseName);
            }
        }
        return str;
    }
    
    public void finishWrite(FileOutputStream str) {
        if (str != null) {
            try {
                str.close();
                mBackupName.delete();
            } catch (IOException e) {
                Log.w("AtomicFile", "finishWrite: Got exception:", e);
            }
        }
    }
    
    public void failWrite(FileOutputStream str) {
        if (str != null) {
            try {
                str.close();
                mBaseName.delete();
                mBackupName.renameTo(mBaseName);
            } catch (IOException e) {
                Log.w("AtomicFile", "failWrite: Got exception:", e);
            }
        }
    }
    
    public FileOutputStream openAppend() throws IOException {
        try {
            return new FileOutputStream(mBaseName, true);
        } catch (FileNotFoundException e) {
            throw new IOException("Couldn't append " + mBaseName);
        }
    }
    
    public void truncate() throws IOException {
        try {
            FileOutputStream fos = new FileOutputStream(mBaseName);
            fos.close();
        } catch (FileNotFoundException e) {
            throw new IOException("Couldn't append " + mBaseName);
        } catch (IOException e) {
        }
    }
    
    public FileInputStream openRead() throws FileNotFoundException {
        if (mBackupName.exists()) {
            mBaseName.delete();
            mBackupName.renameTo(mBaseName);
        }
        return new FileInputStream(mBaseName);
    }
    
    public byte[] readFully() throws IOException {
        FileInputStream stream = openRead();
        try {
            int pos = 0;
            int avail = stream.available();
            byte[] data = new byte[avail];
            while (true) {
                int amt = stream.read(data, pos, data.length-pos);
                //Log.i("foo", "Read " + amt + " bytes at " + pos
                //        + " of avail " + data.length);
                if (amt <= 0) {
                    //Log.i("foo", "**** FINISHED READING: pos=" + pos
                    //        + " len=" + data.length);
                    return data;
                }
                pos += amt;
                avail = stream.available();
                if (avail > data.length-pos) {
                    byte[] newData = new byte[pos+avail];
                    System.arraycopy(data, 0, newData, 0, pos);
                    data = newData;
                }
            }
        } finally {
            stream.close();
        }
    }
}

Other Android examples (source code examples)

Here is a short list of links related to this Android AtomicFile.java source code file:

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