导出工具类增加指定字段导出功能

flossom-common/flossom-common-core/src/main/java/com/flossom/common/core/utils/poi/ExcelUtil.java

@@ -404,7 +404,9 @@ public class ExcelUtil<T> {
      * @return 结果
      */
     public void exportExcel(HttpServletResponse response, List<T> list, String sheetName, List<String> exportFields) {
-        this.exportFields = exportFields;
+        if (exportFields != null && exportFields.size() > 0) {
+            this.exportFields = exportFields;
+        }
         exportExcel(response, list, sheetName, StringUtils.EMPTY);
     }