修复企业微信4.8.0版本MemChangeList解析为空字符串问题

新增 XStreamCDataListConverter 兼容新旧两种格式：
- 旧格式（4.8.0之前）: <MemChangeList><![CDATA[id1,id2]]></MemChangeList>
- 新格式（4.8.0起）: <MemChangeList><Item><![CDATA[id1]]></Item></MemChangeList>

解析结果统一为逗号分隔字符串，保持向后兼容。

Co-authored-by: binarywang <1343140+binarywang@users.noreply.github.com>

Author: Copilot

weixin-java-common/src/main/java/me/chanjar/weixin/common/util/xml/XStreamCDataListConverter.java

@@ -0,0 +1,54 @@
+package me.chanjar.weixin.common.util.xml;
+
+import com.thoughtworks.xstream.converters.Converter;
+import com.thoughtworks.xstream.converters.MarshallingContext;
+import com.thoughtworks.xstream.converters.UnmarshallingContext;
+import com.thoughtworks.xstream.io.HierarchicalStreamReader;
+import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
+
+/**
+ * 兼容两种格式的字符串列表转换器：
+ * <ul>
+ *   <li>旧格式（4.8.0之前）：&lt;MemChangeList&gt;&lt;![CDATA[id1,id2]]&gt;&lt;/MemChangeList&gt;</li>
+ *   <li>新格式（4.8.0起）：&lt;MemChangeList&gt;&lt;Item&gt;&lt;![CDATA[id1]]&gt;&lt;/Item&gt;&lt;/MemChangeList&gt;</li>
+ * </ul>
+ * 解析结果统一为逗号分隔的字符串。
+ */
+public class XStreamCDataListConverter implements Converter {
+
+  @Override
+  public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
+    if (source != null) {
+      writer.setValue("<![CDATA[" + source + "]]>");
+    }
+  }
+
+  @Override
+  public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
+    if (reader.hasMoreChildren()) {
+      // 新格式：含有 <Item> 子元素
+      StringBuilder sb = new StringBuilder();
+      while (reader.hasMoreChildren()) {
+        reader.moveDown();
+        String value = reader.getValue();
+        if (value != null && !value.isEmpty()) {
+          if (sb.length() > 0) {
+            sb.append(",");
+          }
+          sb.append(value);
+        }
+        reader.moveUp();
+      }
+      return sb.length() > 0 ? sb.toString() : null;
+    } else {
+      // 旧格式：直接 CDATA 文本
+      String value = reader.getValue();
+      return (value != null && !value.isEmpty()) ? value : null;
+    }
+  }
+
+  @Override
+  public boolean canConvert(Class type) {
+    return type == String.class;
+  }
+}

weixin-java-cp/src/main/java/me/chanjar/weixin/cp/bean/message/WxCpXmlMessage.java

@@ -11,6 +11,7 @@
 import me.chanjar.weixin.common.util.xml.IntegerArrayConverter;
 import me.chanjar.weixin.common.util.xml.LongArrayConverter;
 import me.chanjar.weixin.common.util.xml.XStreamCDataConverter;
+import me.chanjar.weixin.common.util.xml.XStreamCDataListConverter;
 import me.chanjar.weixin.cp.config.WxCpConfigStorage;
 import me.chanjar.weixin.cp.util.crypto.WxCpCryptUtil;
 import me.chanjar.weixin.cp.util.json.WxCpGsonBuilder;
@@ -156,7 +157,7 @@ public class WxCpXmlMessage implements Serializable {
   private String memChangeCnt;
 
   @XStreamAlias("MemChangeList")
-  @XStreamConverter(value = XStreamCDataConverter.class)
+  @XStreamConverter(value = XStreamCDataListConverter.class)
   private String memChangeList;
 
   @XStreamAlias("LastMemVer")

weixin-java-cp/src/test/java/me/chanjar/weixin/cp/bean/message/WxCpXmlMessageTest.java

@@ -570,5 +570,53 @@ public void testExternalChatChangeEvent() {
     assertEquals(wxMessage3.getUpdateDetail(), "change_name");
     // 当XML中没有MemChangeList元素时，字段应该为null而不是空字符串
     assertThat(wxMessage3.getMemChangeList()).isNull();
+
+    // 测试企业微信4.8.0新格式：MemChangeList使用<Item>子元素（加群场景）
+    String xmlNewFormatAddMember = "<xml>"
+      + "<ToUserName><![CDATA[c2e112dad808119117371bbcd6]]></ToUserName>"
+      + "<FromUserName><![CDATA[sys]]></FromUserName>"
+      + "<CreateTime>9811170016713</CreateTime>"
+      + "<MsgType><![CDATA[event]]></MsgType>"
+      + "<Event><![CDATA[change_external_chat]]></Event>"
+      + "<ChatId><![CDATA[wrxUBwDQAAa44T11Ziaed811rhUr8-3Igmug]]></ChatId>"
+      + "<ChangeType><![CDATA[update]]></ChangeType>"
+      + "<UpdateDetail><![CDATA[add_member]]></UpdateDetail>"
+      + "<JoinScene>3</JoinScene>"
+      + "<MemChangeCnt>1</MemChangeCnt>"
+      + "<MemChangeList><Item><![CDATA[wmxUBwDQAAO-Hn5_wFJz4wvo5TxLFibw]]></Item></MemChangeList>"
+      + "<LastMemVer><![CDATA[5807afd2ab75771d5e8ac623f534ac0b]]></LastMemVer>"
+      + "<CurMemVer><![CDATA[ea36e8b6062b803cda0ee45e9418d637]]></CurMemVer>"
+      + "</xml>";
+    WxCpXmlMessage wxMessage4 = WxCpXmlMessage.fromXml(xmlNewFormatAddMember);
+    assertEquals(wxMessage4.getEvent(), WxCpConsts.EventType.CHANGE_EXTERNAL_CHAT);
+    assertEquals(wxMessage4.getChangeType(), "update");
+    assertEquals(wxMessage4.getUpdateDetail(), "add_member");
+    assertEquals(wxMessage4.getJoinScene(), "3");
+    assertEquals(wxMessage4.getMemChangeCnt(), "1");
+    // 新格式：<Item>子元素中的成员ID应被正确解析
+    assertEquals(wxMessage4.getMemChangeList(), "wmxUBwDQAAO-Hn5_wFJz4wvo5TxLFibw");
+
+    // 测试企业微信4.8.0新格式：多个<Item>子元素（多成员变更）
+    String xmlNewFormatMultiMember = "<xml>"
+      + "<ToUserName><![CDATA[toUser]]></ToUserName>"
+      + "<FromUserName><![CDATA[sys]]></FromUserName>"
+      + "<CreateTime>1403610513</CreateTime>"
+      + "<MsgType><![CDATA[event]]></MsgType>"
+      + "<Event><![CDATA[change_external_chat]]></Event>"
+      + "<ChangeType><![CDATA[update]]></ChangeType>"
+      + "<ChatId><![CDATA[wrOgQhDgAAMYQiS5ol9G7gK9JVAAAA]]></ChatId>"
+      + "<UpdateDetail><![CDATA[del_member]]></UpdateDetail>"
+      + "<QuitScene>1</QuitScene>"
+      + "<MemChangeCnt>2</MemChangeCnt>"
+      + "<MemChangeList>"
+      + "<Item><![CDATA[wmEJiCwAAA9KG2qlSq6rKwASSgAAAA]]></Item>"
+      + "<Item><![CDATA[wmEJiCwAAA9KG2qlSq6rKwBBBBBBB]]></Item>"
+      + "</MemChangeList>"
+      + "</xml>";
+    WxCpXmlMessage wxMessage5 = WxCpXmlMessage.fromXml(xmlNewFormatMultiMember);
+    assertEquals(wxMessage5.getUpdateDetail(), "del_member");
+    assertEquals(wxMessage5.getMemChangeCnt(), "2");
+    // 多个<Item>元素应被解析为逗号分隔字符串
+    assertEquals(wxMessage5.getMemChangeList(), "wmEJiCwAAA9KG2qlSq6rKwASSgAAAA,wmEJiCwAAA9KG2qlSq6rKwBBBBBBB");
   }
 }