Android App data write as file data with synchronous Demo

package com.android.utils;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;

import android.app.Activity;
import android.util.Log;


/**
 * 在一些对数据实时性要求比较高的场合，如随时可能断电的场合下，同时需要将数据写入文件中，
 * 这个时候，我们不希望数据在内存中呆太久，最好能够做到同步，这是我们的需求。<br>
 * 第一种方案：<br>
 *     1. RandomAccessFile<br>
 *     2. public RandomAccessFile(File file, String mode) throws FileNotFoundException<br>
 *      Constructs a new RandomAccessFile based on file and opens it according to the access string in mode. <br>
 *     3. mode may have one of following values: <br>
 *      1. "r" The file is opened in read-only mode. An IOException is thrown if any of the write methods is called. <br>
 *         2. "rw" The file is opened for reading and writing. If the file does not exist, it will be created. <br>
 *         3. "rws" The file is opened for reading and writing. Every change of the file's content or metadata must be written synchronously to the target device. <br>
 *         4. "rwd" The file is opened for reading and writing. Every change of the file's content must be written synchronously to the target device. <br>
 *     4. 由于我们需要其中的数据同步功能，所以我们选择使用包装RandomAccessFile类，实现要求。<br>
 * 第二种方案:<br>
 *  1. FileDescriptor中有sync()方法<br>
        Ensures that data which is buffered within the underlying implementation is written out to the appropriate device before returning.<br>
 *  2. FileOutputStream中的 getFD()方法<br>
        Returns a FileDescriptor which represents the lowest level representation of an operating system stream resource. <br>
 *    3. 使用起来感觉没有RandomAccessFile方便，放弃时使用<br>
 */

public class ZengjfRandomAccessFile {
    /**
     * 将整形数组写入文件
     * 
     * @param filePath         文件路径
     * @param data             整形数组
     * @throws IOException
     */
    static public void writeIntArray(String filePath, int[] data) throws IOException {
        if (null == filePath || null == data) 
            return ;
        
        if (filePath.trim().equals("")) 
            return ;
        
        File file = new File(filePath);
        if (!file.exists()) 
            file.createNewFile();
            
        if (!file.canWrite()) 
            throw new RuntimeException("Zengjf Utils writeIntArray(): no permission for file -- " + filePath + ".");
        
        // write data
        RandomAccessFile raf = new RandomAccessFile(file, "rws");
        for (int i = 0; i < data.length; i++) 
            raf.writeInt(data[i]);
        
        raf.close();
    }

    /**
     * 将整形数组写入文件，文件目录被指定，作为使用者可以不用关心
     * 
     * @param activity         调用这个函数的Activity
     * @param data             要保存的的整形数组
     * @throws IOException
     */
    static public void writeIntArray(Activity activity, int[] data) throws IOException {
        if (null == activity || null == data) 
            return ;

        String filePath = activity.getApplicationContext().getFilesDir().getAbsoluteFile() + "/zengjfData.txt";
        writeIntArray(filePath, data);
    }
    
    /**
     * 从文件中读出长度为length的整形数组
     * 
     * @param filePath        文件路径
     * @param length          数组长度
     * @return                返回数组，如果出错，返回null
     * @throws IOException
     */
    static public int[] readIntArray(String filePath, int length) throws IOException {
        
        if (null == filePath || length <= 0) 
            return null;
        
        if (filePath.trim().equals("")) 
            return null;
        
        File file = new File(filePath);    
        if (!file.canRead()) 
            throw new RuntimeException("Zengjf Utils writeIntArray(): no permission for file -- " + filePath + ".");

        int[] data = new int[length];     // for return data

        // if file not exist in first time and file length less than data size, 
        // just create file and make data for it
        if (!file.exists() || (file.length() < (4 * length))) {
            for (int i = 0; i < data.length; i++) 
                data[i] = 0;

            writeIntArray(filePath, data);
            return data;
        }
        
        //get data
        RandomAccessFile raf = new RandomAccessFile(file, "r");
        for (int i = 0; i < length; i++) 
            data[i] = raf.readInt();
        
        raf.close();
        
        return data;
    }

    /**
     * 从文件中读取整形数组，文件位置、名已经被指定，作为使用者可以不关心
     * 
     * @param activity        调用这个函数的Activity
     * @param length          数组的长度
     * @return                返回数组，如果出错，返回null
     * @throws IOException
     */
    static public int[] readIntArray(Activity activity, int length) throws IOException {
        if (null == activity || 0 == length) 
            return null;

        String filePath = activity.getApplicationContext().getFilesDir().getAbsoluteFile() + "/zengjfData.txt";
        return readIntArray(filePath, length);
    }
    
    /**
     * 往文件中写入原始整形数组，其实就是填充整形0
     * 
     * @param filePath        文件路径
     * @param length          数组大小
     * @throws IOException
     */
    static public void writeRawIntArray(String filePath, int length) throws IOException {

        if (null == filePath || length <= 0) 
            return ;
        
        if (filePath.trim().equals("")) 
            return ;

        File file = new File(filePath);    
        int[] data = new int[length];     // for return data

        // if file not exist in first time, just create file and make data for it
        if (file.exists()) {
            for (int i = 0; i < data.length; i++) 
                data[i] = 0;

            writeIntArray(filePath, data);
        }
    }
    
    /**
     * 
     * 往文件中写入值为0的整形数组，文件位置、名已经被指定，作为使用者可以不关心
     * 
     * @param activity        调用这个函数的Activity
     * @param length          写入数组的长度
     * @throws IOException
     */
    static public void writeRawIntArray(Activity activity, int length) throws IOException{
        if (null == activity || 0 == length) 
            return ;

        String filePath = activity.getApplicationContext().getFilesDir().getAbsoluteFile() + "/zengjfData.txt";
        writeRawIntArray(filePath, length);
    }
    
    /**
     * 测试用的的Demo
     * @param activity     调用这个函数的Activity
     */
    static public void testDemo(Activity activity) {
        int[] data = {1, 2, 3, 4, 5, 6};
        try {
            writeIntArray(activity, data);
            int[] redata = readIntArray(activity, 6);
            Log.e("zengjf utils", Arrays.toString(redata));
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}