JAVA文件加密解密

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<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;
		 }
	 
	
}