文件加密解密

package com.mall.common;

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<r;i++)
                {
                    byte b=buffer[i];
                    buffer2[i]=b==255?0:++b;
                }
                out.write(buffer2, 0, r);
                out.flush();
        }
        in.close();
        out.close();
        file.delete();
        dest.renameTo(new File(fileUrl));
        appendMethodA(fileUrl, key);
        System.out.println("加密成功");
    }
     
    /**
     * 
     * @param fileName
     * @param content 密钥
     */
     public static void appendMethodA(String fileName, String content) {
            try {
                // 打开一个随机访问文件流，按读写方式
                RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw");
                // 文件长度，字节数
                long fileLength = randomFile.length();
                //将写文件指针移到文件尾。
                randomFile.seek(fileLength);
                randomFile.writeBytes(content);
                randomFile.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
     }
     /**
      * 解密
      * @param fileUrl 源文件
      * @param tempUrl 临时文件
      * @param ketLength 密码长度
      * @return
      * @throws Exception
      */
     public static String decrypt(String fileUrl, String tempUrl, int keyLength) throws Exception{
            File file = new File(fileUrl);
            if (!file.exists()) {
                return null;
            }
            File dest = new File(tempUrl);
            if (!dest.getParentFile().exists()) {
                dest.getParentFile().mkdirs();
            }
             
            InputStream is = new FileInputStream(fileUrl);
            OutputStream out = new FileOutputStream(tempUrl);
             
            byte[] buffer = new byte[1024];
            byte[] buffer2=new byte[1024];
            byte bMax=(byte)255;
            long size = file.length() - keyLength;
            int mod = (int) (size%1024);
            int div = (int) (size>>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;
         }
     
     public static void main(String[] args){
         try {
            FileEncryptAndDecrypt.encrypt("E:\Users\aa .doc","abc");
            FileEncryptAndDecrypt.decrypt("E:\Users\aa .doc","E:\Users\bb .doc",3); 
         } catch (Exception e) { 
           // TODO Auto-generated catch block  
           e.printStackTrace(); 
         } 
     } 
}