🎨 #3880 【企业微信】修复MemChangeList群成员变更ID解析为空字符串的问题

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;
+  }
+}