使用MD5对数据库密码进行加密的实例

package com.lxitedu.tools.generate;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import com.dcivision.framework.Crypt;
import com.dcivision.framework.SystemParameterConstant;
import com.dcivision.framework.SystemParameterFactory;

/**
* suit the php
*
* @author Administrator
*
*/
public class MD5 {

  // 解密类： Crypt
  private final static String[] hexDigits = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d",
      "e", "f"                           };

  public static void main(String[] args) throws Exception {
    getMD5EncryptedString("");
    String encrptedPwd = Crypt.encrypt("diaoer",
        SystemParameterFactory.getSystemParameter(SystemParameterConstant.CRYPTO_SALT));
    System.out.println(getMD5EncryptedString("diaoer"));
    System.out.println(encrptedPwd);
  }

  public static String getMD5EncryptedString(String sourceString) throws NoSuchAlgorithmException {
    // 加密后的字符串
    // 创建具有指定算法名称的信息摘要
    MessageDigest md = MessageDigest.getInstance("MD5");
    // 使用指定的字节数组对摘要进行最后更新，然后完成摘要计算
    byte[] results = md.digest(sourceString.getBytes());
    return byteArrayToHexString(results);
  }

  private static String byteArrayToHexString(byte[] b) {
    StringBuffer resultSb = new StringBuffer();
    for (int i = 0; i < b.length; i++) {
      resultSb.append(byteToHexString(b[i]));
    }
    return resultSb.toString();
  }

  /**
   * 将一个字节转化成十六进制形式的字符串
   */
  private static String byteToHexString(byte b) {
    int n = b;
    if (n < 0)
      n = 256 + n;
    int d1 = n / 16;
    int d2 = n % 16;
    return hexDigits[d1] + hexDigits[d2];
  }

}





解密：
/*
* @(#)Crypt.java
*
* Copyright (c) 2003 DCIVision Ltd
* All rights reserved.
*
* This software is the confidential and proprietary information of DCIVision
* Ltd ("Confidential Information").  You shall not disclose such Confidential
* Information and shall use it only in accordance with the terms of the license
* agreement you entered into with DCIVision Ltd.
*/
package com.dcivision.framework;

/**
* Crypt.java
*
* This class is to provide encrypt and decrypt function by a password provided.
*
* @author Rollo Chan
* @company DCIVision Limited
* @creation date 25/06/2003
* @version $Revision: 1.6 $
*/

public class Crypt {

  public static final String REVISION = "$Revision: 1.6 $";

  private Crypt() {
  }

  /**
   * encrypt
   *
   * Encrypt a string with a password
   *
   * @param buffer
   *          The buffer to be encrypted
   * @param password
   *          The password
   */
  public static String encrypt(String buffer, String password) {
    StringBuffer sbSpace = new StringBuffer("     ");
    buffer = sbSpace.toString() + buffer + sbSpace.toString();
    char[] temp = new char[buffer.length()];

    int a = 0;
    for (int i = 0; i < buffer.length(); i++) {
      int b = password.charAt(a);
      a++;
      if (a >= password.length()) {
        a = 0;
      }
      int c = (int) buffer.charAt(i);
      temp[i] = (char) (c ^ b);
    }
    return toHex(temp);
  }

  /**
   * decrypt
   *
   * Decrypt a string with a password
   *
   * @param buffer
   *          The buffer to be decrypted
   * @param password
   *          The password
   */
  public static String decrypt(String buffer, String password) {
    char[] temp = toChar(buffer);
    String result = "";
    int a = 0;
    for (int i = 0; i < temp.length; i++) {
      int b = password.charAt(a);
      a++;
      if (a >= password.length()) {
        a = 0;
      }
      int c = temp[i];
      result += (char) (c ^ b);// ^ 按位异或XOR 就是二个操作数只有一个是1的话结果就是 1 否则就是 0 。
    }
    return result.trim();
  }

  private static int hexToInt(char c) {
    if (c >= '0' && c <= '9') {
      return c - '0';
    }
    return (c - 'a') + 10;
  }

  private static char hexToChar(String buffer) {
    int l = hexToInt(buffer.charAt(1));
    int h = hexToInt(buffer.charAt(0));
    return (char) (h * 16 + l);
  }

  private static String toHex(char[] buffer) {
    String temp = "";
    String result = "";
    for (int i = 0; i < buffer.length; i++) {
      int c = buffer[i];
      temp = Integer.toHexString((int) c);
      if (temp.length() == 1) {
        temp = "0" + temp;
      }
      result += temp;
    }
    return result;
  }

  private static char[] toChar(String buffer) {
    char[] result = new char[buffer.length() / 2];
    for (int i = 0; i < buffer.length(); i += 2) {
      if (i + 2 <= buffer.length()) {
        String temp = buffer.substring(i, i + 2);
        result[i / 2] = (char) hexToChar(temp);
      }
    }
    return result;
  }

  /**
   * main
   *
   * @param arg
   */
  public static void main(String arg[]) {
    // String buffer = arg[0];
    // String password = arg[1];
    String buffer = "diaoer";
    String password = "test";
    String temp = Crypt.encrypt(buffer, password);
    System.out.println("buffer    = \"" + buffer + "\"");
    System.out.println("password  = \"" + password + "\"");
    System.out.println("encrypted = \"" + temp + "\"");
    System.out.println("decrypted = \"" + Crypt.decrypt(temp, password) + "\"");
  }
}