Java 关于原生的MD5加密的使用方法，下面直接上代码了

snowcoal.com

package test.demo001;
import java.security.MessageDigest;
public class MD5Util {
  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();
      // MD5摘要
      MessageDigest mdInst = MessageDigest.getInstance("MD5");
      // 指定的字节更新摘要
      mdInst.update(btInput);
      // 密文
      byte[] md = mdInst.digest();
      // 将密文转换成十六进制的字符串
      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;
    }
  }
  public static void main(String[] args) {
    System.out.println(testClass.MD5("20121220"));
    //486B54009AC2BA6BDE21ACA441BE9BB2
    System.out.println(testClass.MD5("Encrypt"));
    //611D29C748A7931C825A247FCF3F290E
  }
}

下面是关于进制转换，方便调试（非常有用）：

1：string to hexsnowcoal.com

//String to byte
private byte[] StringToHex(String s){
  int n = s.length()/2;
  byte[] r = new byte[n];
  for (int i = 0; i < n; i ++) {
    char a = s.charAt(i*2);
    char b = s.charAt(i*2 + 1);
    r[i]=(byte) ((CharToInt(a) << 4) | CharToInt(b));
   }
  return r;
}

2：char to intsnowcoal.com

private static int CharToInt(char ch) {
     if ('a' <= ch && ch <= 'f') { return ch - 'a' + 10; }
     if ('A' <= ch && ch <= 'F') { return ch - 'A' + 10; }
     if ('0' <= ch && ch <= '9') { return ch - '0'; }
     throw new IllegalArgumentException(String.valueOf(ch));
  }

3：hex to stringsnowcoal.com

//print hex to string
private String HexToString(byte[] byBuf, int len){
    String res ="";
    for (int i = 0; i < len; i++)  {//byBuf.length
      String hex = Integer.toHexString(byBuf[i] & 0xFF);
      if (hex.length() == 1) {
        hex = '0' + hex;
      }
      res +=hex.toUpperCase();
    }
    return res;
  }