java 实现MD5加密算法的简单实例

java 实现md5加密算法的简单实例

实现代码：

import java.security.nosuchalgorithmexception;  
 
public class md5hashutil  
{  
private messagedigest md = null;  
private static md5hashutil md5 = null;  
private static final char[] hexchars ={'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};  
 
  /** 
  * constructor is private so you must use the getinstance method 
  */  
  private md5hashutil() throws nosuchalgorithmexception  
  {  
   md = messagedigest.getinstance("md5");  
  }  
  /** 
  * this returns the singleton instance 
  */  
 public static md5hashutil getinstance()throws nosuchalgorithmexception  
  {  
    if (md5 == null)  
    {  
     md5 = new md5hashutil();  
   }  
   return (md5);  
  }  
 public static string hashcode(string datatohash) throws nosuchalgorithmexception{  
 return getinstance().hashdata(datatohash.getbytes());  
 }  
 public static string hashcode(byte[] datatohash) throws nosuchalgorithmexception{  
 return getinstance().hashdata(datatohash);  
 }  
public string hashdata(byte[] datatohash) {  
   return hexstringfrombytes((calculatehash(datatohash))).tolowercase();  
}  
private byte[] calculatehash(byte[] datatohash)  
{  
   md.update(datatohash, 0, datatohash.length);  
   return (md.digest());  
 }  
public string hexstringfrombytes(byte[] b)  
{  
  string hex = "";  
  int msb;  
  int lsb = 0;  
  int i;  
  // msb maps to idx 0  
  for (i = 0; i < b.length; i++)  
  {  
   msb = ((int)b[i] & 0x000000ff) / 16;  
   lsb = ((int)b[i] & 0x000000ff) % 16;  
    hex = hex + hexchars[msb] + hexchars[lsb];  
   }  
   return(hex);  
  }  
 
public static void main(string args[]) throws nosuchalgorithmexception  
{  
string string = "my name is zhangli";  
system.out.println(string);  
system.out.println(hashcode(string));  
}  
}  

 如上代码为java语言实现md5加密算法，输出为加密后的密文！

通常将加密后的密文保存在数据库中，如果需要比较只比较他们的用md5加密过后的密文。

同时，md5加密算法是不可逆的，破解的难度很高。

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