/**自定义实现简单的文件加密解密工具 
 * Created by zhangshuo on 2016/6/28. 
 */ 
public class CustomFileCipherUtil { 
 
  /** 
   * 加密后的文件的后缀 
   */ 
  public static final String CIPHER_TEXT_SUFFIX = ".cipher"; 
 
  /** 
   * 加解密时以32K个字节为单位进行加解密计算 
   */ 
  private static final int CIPHER_BUFFER_LENGHT = 32 * 1024; 
 
  /** 
   * 加密，这里主要是演示加密的原理，没有用什么实际的加密算法 
   * 
   * @param filePath 明文文件绝对路径 
   * @return 
   */ 
  public static boolean encrypt(String filePath, CipherListener listener) { 
    try { 
      long startTime = System.currentTimeMillis(); 
      File f = new File(filePath); 
      RandomAccessFile raf = new RandomAccessFile(f, "rw"); 
      long totalLenght = raf.length(); 
      FileChannel channel = raf.getChannel(); 
 
      long multiples = totalLenght / CIPHER_BUFFER_LENGHT; 
      long remainder = totalLenght % CIPHER_BUFFER_LENGHT; 
 
      MappedByteBuffer buffer = null; 
      byte tmp; 
      byte rawByte; 
 
      //先对整除部分加密 
      for(int i = 0; i < multiples; i++){ 
        buffer = channel.map( 
            FileChannel.MapMode.READ_WRITE, i * CIPHER_BUFFER_LENGHT, (i + 1) * CIPHER_BUFFER_LENGHT); 
 
        //此处的加密方法很简单，只是简单的异或计算 
        for (int j = 0; j < CIPHER_BUFFER_LENGHT; ++j) { 
          rawByte = buffer.get(j); 
          tmp = (byte) (rawByte ^ j); 
          buffer.put(j, tmp); 
 
          if(null != listener){ 
            listener.onProgress(i * CIPHER_BUFFER_LENGHT + j, totalLenght); 
          } 
        } 
        buffer.force(); 
        buffer.clear(); 
      } 
 
      //对余数部分加密 
      buffer = channel.map( 
          FileChannel.MapMode.READ_WRITE, multiples * CIPHER_BUFFER_LENGHT, multiples * CIPHER_BUFFER_LENGHT + remainder); 
 
      for (int j = 0; j < remainder; ++j) { 
        rawByte = buffer.get(j); 
        tmp = (byte) (rawByte ^ j); 
        buffer.put(j, tmp); 
 
        if(null != listener){ 
          listener.onProgress(multiples * CIPHER_BUFFER_LENGHT + j, totalLenght); 
        } 
      } 
      buffer.force(); 
      buffer.clear(); 
 
      channel.close(); 
      raf.close(); 
 
      //对加密后的文件重命名，增加.cipher后缀 
//      f.renameTo(new File(f.getPath() + CIPHER_TEXT_SUFFIX)); 
      Log.d("加密用时：", (System.currentTimeMillis() - startTime) /1000 + "s"); 
      return true; 
    } catch (Exception e) { 
      e.printStackTrace(); 
      return false; 
    } 
  } 
 
 
  /** 
   * 解密，这里主要是演示加密的原理，没有用什么实际的加密算法 
   * 
   * @param filePath 密文文件绝对路径，文件需要以.cipher结尾才会认为其实可解密密文 
   * @return 
   */ 
  public static boolean decrypt(String filePath, CipherListener listener) { 
    try { 
      long startTime = System.currentTimeMillis(); 
      File f = new File(filePath); 
//      if(!f.getPath().toLowerCase().endsWith(CIPHER_TEXT_SUFFIX)){ 
//        //后缀不同，认为是不可解密的密文 
//        return false; 
//      } 
 
      RandomAccessFile raf = new RandomAccessFile(f, "rw"); 
      long totalLenght = raf.length(); 
      FileChannel channel = raf.getChannel(); 
 
      long multiples = totalLenght / CIPHER_BUFFER_LENGHT; 
      long remainder = totalLenght % CIPHER_BUFFER_LENGHT; 
 
      MappedByteBuffer buffer = null; 
      byte tmp; 
      byte rawByte; 
 
      //先对整除部分解密 
      for(int i = 0; i < multiples; i++){ 
        buffer = channel.map( 
            FileChannel.MapMode.READ_WRITE, i * CIPHER_BUFFER_LENGHT, (i + 1) * CIPHER_BUFFER_LENGHT); 
 
        //此处的解密方法很简单，只是简单的异或计算 
        for (int j = 0; j < CIPHER_BUFFER_LENGHT; ++j) { 
          rawByte = buffer.get(j); 
          tmp = (byte) (rawByte ^ j); 
          buffer.put(j, tmp); 
 
          if(null != listener){ 
            listener.onProgress(i * CIPHER_BUFFER_LENGHT + j, totalLenght); 
          } 
        } 
        buffer.force(); 
        buffer.clear(); 
      } 
 
      //对余数部分解密 
      buffer = channel.map( 
          FileChannel.MapMode.READ_WRITE, multiples * CIPHER_BUFFER_LENGHT, multiples * CIPHER_BUFFER_LENGHT + remainder); 
 
      for (int j = 0; j < remainder; ++j) { 
        rawByte = buffer.get(j); 
        tmp = (byte) (rawByte ^ j); 
        buffer.put(j, tmp); 
 
        if(null != listener){ 
          listener.onProgress(multiples * CIPHER_BUFFER_LENGHT + j, totalLenght); 
        } 
      } 
      buffer.force(); 
      buffer.clear(); 
 
      channel.close(); 
      raf.close(); 
 
      //对加密后的文件重命名，增加.cipher后缀 
//      f.renameTo(new File(f.getPath().substring(f.getPath().toLowerCase().indexOf(CIPHER_TEXT_SUFFIX)))); 
 
      Log.d("解密用时：", (System.currentTimeMillis() - startTime) / 1000 + "s"); 
      return true; 
    } catch (Exception e) { 
      e.printStackTrace(); 
      return false; 
    } 
  } 
 
  /** 
   * 用于加解密进度的监听器 
   */ 
  public interface CipherListener{ 
    void onProgress(long current, long total); 
  } 
}