Vaadin表单字段高级验证：空值放行与非空正则校验的实现策略

binder.forField(field)
      .withValidator(fieldValue -> fieldValue.matches(REGEX),
          FORMAT_ERROR_MSG)
      .bind("fieldName");

import com.vaadin.flow.data.binder.Binder;
import com.vaadin.flow.component.textfield.TextField;
import com.vaadin.flow.component.button.Button;
import com.vaadin.flow.component.notification.Notification;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.router.Route;

@Route("flexible-validation")
public class FlexibleValidationView extends VerticalLayout {

    // 示例：一个简单的邮箱地址正则表达式
    private static final String REGEX = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6}$";
    private static final String FORMAT_ERROR_MSG = "请输入有效的邮箱地址";

    public FlexibleValidationView() {
        // 创建一个可选的邮箱输入框
        TextField emailField = new TextField("邮箱 (可选)");
        Button submitButton = new Button("提交");

        // 初始化Binder，绑定到MyFormData数据模型
        Binder<MyFormData> binder = new Binder<>(MyFormData.class);

        // 核心解决方案：修改验证器逻辑
        binder.forField(emailField)
              // 验证器逻辑：如果值为null或为空字符串，则通过；否则进行正则表达式匹配
              .withValidator(value -> value == null || value.isEmpty() || value.matches(REGEX),
                  FORMAT_ERROR_MSG)
              // 绑定到数据模型的email属性
              .bind(MyFormData::getEmail, MyFormData::setEmail);

        // 配置提交按钮的点击事件
        submitButton.addClickListener(event -> {
            try {
                MyFormData formData = new MyFormData();
                // 尝试将表单数据写入Bean，并执行验证
                if (binder.writeBeanIfValid(formData)) {
                    Notification.show("表单提交成功! 邮箱: " + (formData.getEmail() != null && !formData.getEmail().isEmpty() ? formData.getEmail() : "空"));
                } else {
                    Notification.show("表单验证失败，请检查输入", 3000, Notification.Position.MIDDLE);
                }
            } catch (Exception e) {
                Notification.show("保存数据时发生错误: " + e.getMessage(), 3000, Notification.Position.MIDDLE);
            }
        });

        // 将组件添加到布局中
        add(emailField, submitButton);
    }

    // 示例数据模型类
    public static class MyFormData {
        private String email;

        public String getEmail() {
            return email;
        }

        public void setEmail(String email) {
            this.email = email;
        }
    }
}

value -> value == null || value.isEmpty() || value.matches(REGEX)