diff --git a/weixin-java-pay/src/main/java/com/github/binarywang/wxpay/util/SignUtils.java b/weixin-java-pay/src/main/java/com/github/binarywang/wxpay/util/SignUtils.java
index 471298724..5591b016b 100644
--- a/weixin-java-pay/src/main/java/com/github/binarywang/wxpay/util/SignUtils.java
+++ b/weixin-java-pay/src/main/java/com/github/binarywang/wxpay/util/SignUtils.java
@@ -1,18 +1,5 @@
 package com.github.binarywang.wxpay.util;
 
-import java.lang.reflect.Field;
-import java.lang.reflect.Modifier;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-import java.util.Map;
-import java.util.SortedMap;
-import java.util.TreeMap;
-
-import org.apache.commons.codec.digest.DigestUtils;
-import org.apache.commons.lang3.ArrayUtils;
-import org.apache.commons.lang3.StringUtils;
-
 import com.github.binarywang.wxpay.bean.request.BaseWxPayRequest;
 import com.github.binarywang.wxpay.bean.result.BaseWxPayResult;
 import com.github.binarywang.wxpay.constant.WxPayConstants.SignType;
@@ -20,6 +7,13 @@ import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.thoughtworks.xstream.annotations.XStreamAlias;
 import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.codec.digest.DigestUtils;
+import org.apache.commons.lang3.ArrayUtils;
+import org.apache.commons.lang3.StringUtils;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.*;
 
 /**
  * <pre>
@@ -31,6 +25,12 @@ import lombok.extern.slf4j.Slf4j;
  */
 @Slf4j
 public class SignUtils {
+
+  /**
+   * 签名的时候不携带的参数
+   */
+  private static List<String> NO_SIGN_PARAMS = Lists.newArrayList("sign", "key", "xmlString", "xmlDoc", "couponList");
+
   /**
    * 请参考并使用 {@link #createSign(Object, String, String, String[])}.
    *
@@ -85,7 +85,7 @@ public class SignUtils {
       String value = params.get(key);
       boolean shouldSign = false;
       if (StringUtils.isNotEmpty(value) && !ArrayUtils.contains(ignoredParams, key)
-        && !Lists.newArrayList("sign", "key", "xmlString", "xmlDoc", "couponList").contains(key)) {
+        && !NO_SIGN_PARAMS.contains(key)) {
         shouldSign = true;
       }