Getting Started With Your API

import com.alibaba.fastjson.JSONObject;
import org.apache.commons.lang3.StringUtils;
import org.springframework.util.DigestUtils;

import java.util.Map;
import java.util.TreeMap;


/**
*  Parameter signing and verification
*/
public class SignUtil {

   private static final String SIGN = "sign";

   /**
    * Send signature 
    */
   public static String sendSign(String password, TreeMap<String, String> paramMap) {
       paramMap.remove(SIGN);
       StringBuilder sb = new StringBuilder();
       for (Map.Entry<String, String> entry : paramMap.entrySet()) {
           if (StringUtils.isNotBlank(entry.getValue())) {
               sb.append(entry.getKey());
               sb.append(entry.getValue());
           }
       }
       return DigestUtils.md5DigestAsHex((sb.toString() + password).getBytes()).toLowerCase();
   }

   /**
    * Send signature 
    */
   public static boolean verifySendSign(String password, TreeMap<String, String> paramMap) {
       String sign = paramMap.remove(SIGN);
       String computed = sendSign(password, paramMap);
       return StringUtils.equals(sign, computed);
   }


   public static void main(String[] args) {
       /**Send signature verification*/
       String password = "4Z7bMS1eLI6895";
       TreeMap<String, String> paramMap = new TreeMap<>();
       paramMap.put("nonce", "222222");
       paramMap.put("account", "IM6742671");
       paramMap.put("mobile", "8618916198813");
       paramMap.put("msg", "test 666661 ");
       System.out.println(JSONObject.toJSONString(paramMap));
       String sign = sendSign(password, paramMap);
       System.out.println(sign);

       TreeMap<String, String> newParamMap = new TreeMap<>(paramMap);
       newParamMap.put(SIGN, sign);

       boolean validate = verifySendSign(password, newParamMap);
       System.out.println(validate);

   }
}