Java实现文件的加密解密功能示例

package com.copy.encrypt;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
public class FileEncryptAndDecrypt {
  /**
   * 文件file进行加密
   * @param fileUrl 文件路径
   * @param key 密码
   * @throws Exception
   */
  public static void encrypt(String fileUrl, String key) throws Exception {
    File file = new File(fileUrl);
    String path = file.getPath();
    if(!file.exists()){
      return;
    }
    int index = path.lastIndexOf("\\");
    String destFile = path.substring(0, index)+"\\"+"abc";
    File dest = new File(destFile);
    InputStream in = new FileInputStream(fileUrl);
    OutputStream out = new FileOutputStream(destFile);
    byte[] buffer = new byte[1024];
    int r;
    byte[] buffer2=new byte[1024];
    while (( r= in.read(buffer)) > 0) {
        for(int i=0;i>10);
      int count = mod==0?div:(div+1);
      int k = 1, r;
      while ((k <= count && ( r = is.read(buffer)) > 0)) {
        if(mod != 0 && k==count) {
          r = mod;
        }
        for(int i = 0;i < r;i++)
        {
          byte b=buffer[i];
          buffer2[i]=b==0?bMax:--b;
        }
        out.write(buffer2, 0, r);
        k++;
      }
      out.close();
      is.close();
      return tempUrl;
    }
   /**
   * 判断文件是否加密
   * @param fileName
   * @return
   */
   public static String readFileLastByte(String fileName, int keyLength) {
     File file = new File(fileName);
     if(!file.exists())return null;
     StringBuffer str = new StringBuffer();
      try {
        // 打开一个随机访问文件流，按读写方式
        RandomAccessFile randomFile = new RandomAccessFile(fileName, "r");
        // 文件长度，字节数
        long fileLength = randomFile.length();
        //将写文件指针移到文件尾。
        for(int i = keyLength ; i>=1 ; i--){
          randomFile.seek(fileLength-i);
          str.append((char)randomFile.read());
        }
        randomFile.close();
        return str.toString();
      } catch (IOException e) {
        e.printStackTrace();
      }
      return null;
     }
}