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();
         }
     }
 }