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;

		 }

	 

	

}