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。

来源：http://blog.csdn.net/fzhlee/article/details/5724530