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();
}
}
}