fix(structs): resolve calc input result and add utf-8/meta plus form validation

src/main/java/com/example/struts2/UserFormAction.java

@@ -68,6 +68,22 @@ public class UserFormAction extends ActionSupport {
         return SUCCESS;
     }
     
+    @Override
+    public void validate() {
+        if (user == null) {
+            return;
+        }
+        if (user.getName() == null || user.getName().trim().isEmpty()) {
+            addFieldError("user.name", "姓名不能为空");
+        }
+        if (user.getEmail() == null || !user.getEmail().contains("@")) {
+            addFieldError("user.email", "邮箱格式不正确");
+        }
+        if (user.getAge() == null || user.getAge() < 1 || user.getAge() > 120) {
+            addFieldError("user.age", "年龄必须在 1 到 120 之间");
+        }
+    }
+
     // Getters and Setters
     public User getUser() { return user; }
     public void setUser(User user) { this.user = user; }