diff --git a/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageApi.java b/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageApi.java
index 582fb334..636a6b05 100644
--- a/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageApi.java
+++ b/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageApi.java
@@ -1,11 +1,17 @@
 package com.foxinmy.weixin4j.wxa.api;
 
-import com.foxinmy.weixin4j.exception.WeixinException;
-import com.foxinmy.weixin4j.token.TokenManager;
-
 import java.util.Map;
 import java.util.Properties;
 
+import com.foxinmy.weixin4j.exception.WeixinException;
+import com.foxinmy.weixin4j.token.TokenManager;
+
+/**
+ * 发送订阅消息。
+ *
+ * <a href="https://developers.weixin.qq.com/miniprogram/dev/api-backend/open-api/subscribe-message/subscribeMessage.send.html">发送订阅消息</a>
+ * @since 1.9
+ */
 public class SubscribeMessageApi extends TokenManagerApi {
 
 	public SubscribeMessageApi(TokenManager tokenManager) {
diff --git a/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageParameter.java b/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageParameter.java
index f7c07fb2..423e3117 100644
--- a/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageParameter.java
+++ b/weixin4j-wxa/src/main/java/com/foxinmy/weixin4j/wxa/api/SubscribeMessageParameter.java
@@ -1,12 +1,12 @@
 package com.foxinmy.weixin4j.wxa.api;
 
-import com.alibaba.fastjson.annotation.JSONField;
-
 import java.io.Serializable;
 import java.util.HashMap;
 import java.util.Map;
 
-class SubscribeMessageParameter {
+import com.alibaba.fastjson.annotation.JSONField;
+
+class SubscribeMessageParameter implements Serializable {
 
 	private static final long serialVersionUID = 2018052601L;