java 自带md5加密详解编程语言

package test; 
import java.security.MessageDigest; 
import java.security.NoSuchAlgorithmException; 
public class MD5Util { 
    //第一种实现 
    public final static String MD5(String s) { 
        char hexDigits[]={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};        
        try { 
            byte[] btInput = s.getBytes(); 
            // 获得MD5摘要算法的 MessageDigest 对象 
            MessageDigest mdInst = MessageDigest.getInstance("MD5"); 
            // 使用指定的字节更新摘要 
            mdInst.update(btInput); 
            // 获得密文 
            byte[] md = mdInst.digest(); 
            // 把密文转换成十六进制的字符串形式 
            int j = md.length; 
            char str[] = new char[j * 2]; 
            int k = 0; 
            for (int i = 0; i < j; i++) { 
                byte byte0 = md[i]; 
                str[k++] = hexDigits[byte0 >>> 4 & 0xf]; 
                str[k++] = hexDigits[byte0 & 0xf]; 
            } 
            return new String(str); 
        } catch (Exception e) { 
            e.printStackTrace(); 
            return null; 
        } 
    } 
    //第二种实现 
    public final static String MD(String str) {//项目中的 
        try { 
              MessageDigest md5 = MessageDigest.getInstance("MD5"); 
              md5.update(str.getBytes()); 
              byte b[] = md5.digest(); 
 
              StringBuffer sb = new StringBuffer(""); 
              for (int n = 0; n < b.length; n++) { 
                int i = b[n]; 
                if (i < 0) i += 256; 
                if (i < 16) sb.append("0"); 
                sb.append(Integer.toHexString(i)); 
              } 
              return sb.toString();  //32位加密 
            } catch (NoSuchAlgorithmException e) { 
              e.printStackTrace(); 
              return null; 
            } 
    } 
    public static void main(String[] args) { 
        System.out.println(MD5Util.MD5("111")); 
        System.out.println(MD5Util.MD("111")); 
    } 
}