public class Md5 {

    //十六進制下數字到字符的映射數組

    private static final char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',

            'A', 'B', 'C', 'D', 'E', 'F' };

    /**把inputString加密*/

    public static String md5Str(String inputStr){

        return encrypt(inputStr);

    }

    public static String encrypt(String inputStr) {

        byte[] inStrBytes = inputStr.getBytes();

        try {

            //創建具有指定算法名稱的信息摘要

            MessageDigest MD = MessageDigest.getInstance("MD5");

            //使用指定的字節數組對摘要進行最后更新，然后完成摘要計算

            MD.update(inStrBytes);

            byte[] mdByte = MD.digest();

            char[] str = new char[mdByte.length * 2];

            int k = 0;

            for(int i=0;i<mdByte.length;i++) {

                byte temp = mdByte[i];

                str[k++] = hexDigits[temp >>> 4 & 0xf];

                str[k++] = hexDigits[temp & 0xf];

            }

            return new String(str);

        } catch (NoSuchAlgorithmException e) {

            e.printStackTrace();

        }

        return null;

    }

}

import java.io.UnsupportedEncodingException;

import java.security.InvalidKeyException;

import java.security.NoSuchAlgorithmException;

import java.util.TreeMap;

public class SJS {

    //entrance

    /**

     * 對請求參數進行加密

     * @param requestParams 請求參數

     * @param secret 根秘鑰

     * @return

     * @throws Exception

     */

    public String getSJSInfo(TreeMap<String, Object> requestParams, String secret) throws Exception {

        return sjsSi(buildParamStr(requestParams), secret);

    }

    //調用MD5封裝方法進行加密【入參+secret】

    private String sjsSi(String signStr, String secret)

        throws NoSuchAlgorithmException, UnsupportedEncodingException, InvalidKeyException {

        return Md5.md5Str(signStr+secret);

    }

    //將入參（格式key=value）與&進行拼接，并返回

    public String buildParamStr(TreeMap<String, Object> requestParams) {

        StringBuilder retStr = new StringBuilder();

        for(String key: requestParams.keySet()) {

            if (retStr.length()==0) {

                retStr.append(key+"="+String.valueOf(requestParams.get(key)));

            } else {

                retStr.append("&"+key+"="+String.valueOf(requestParams.get(key)));

            }

        }

        return retStr.toString();

    }

}