消息摘要--文件校验

import java.io.File;

import java.io.FileInputStream;

import java.security.DigestInputStream;

import java.security.MessageDigest;

import static org.junit.Assert.*;

import org.apache.commons.codec.binary.Hex;

import org.apache.commons.codec.digest.DigestUtils;

public class FileMD5 {

        public static String checkMessageDigest() throws Exception{

              FileInputStream fis= new FileInputStream(new File("E:/ACM/in.txt"));

               //初始化，并指定md5算法

              DigestInputStream dis= new DigestInputStream(fis,MessageDigest.getInstance( "md5"));

              

               byte[] buffer=new byte[1024];

               int readLen=dis.read(buffer,0,1024);//读，并且会update这个message digest

               while(readLen>-1){

                     readLen=dis.read(buffer, 0, 1024);

              }

              dis.close();

              

              MessageDigest md=dis.getMessageDigest(); //获取消息摘要对象

               byte[] b=md.digest();//摘要处理

               //十六进制处理

              String md5Hex=Hex. encodeHexString(b);

              System. out.println(md5Hex);

               return md5Hex;

       }

       

        public static String checkMessageDigestUtils() throws Exception{

              FileInputStream fis= new FileInputStream(new File("E:/ACM/in.txt"));

              String md5Hex=DigestUtils.md5Hex(fis);//包装，并获取md5，十六进制

              fis.close();

              System. out.println(md5Hex);

               return md5Hex;

       }

       

        public static void main(String[] args) throws Exception {

               // TODO Auto-generated method stub

              String md51= checkMessageDigest();

              String md52= checkMessageDigestUtils();

               assertEquals(md51,md52);//判断两个方法计算的MD5值是否一致，不一致会抛出异常

       }

}