Vaadin表单中可选字段的条件验证：允许为空但非空时强制校验

import com.vaadin.flow.data.binder.Binder;
import com.vaadin.flow.component.textfield.TextField;

// 假设在一个组件或视图中
public class MyForm extends Div {
    private TextField field = new TextField("可选字段");
    private Binder<MyDataModel> binder = new Binder<>(MyDataModel.class);

    private static final String REGEX = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6}$"; // 示例：邮箱正则表达式
    private static final String FORMAT_ERROR_MSG = "格式不正确";

    public MyForm() {
        // ... 其他组件初始化
        binder.forField(field)
              .withValidator(value -> value.matches(REGEX), FORMAT_ERROR_MSG)
              .bind(MyDataModel::getField, MyDataModel::setField); // 假设MyDataModel有一个getField/setField方法

        // 添加字段到布局
        add(field);
    }
}

import com.vaadin.flow.data.binder.Binder;
import com.vaadin.flow.component.textfield.TextField;
import com.vaadin.flow.component.html.Div;
import com.vaadin.flow.component.button.Button;
import com.vaadin.flow.component.notification.Notification;

public class OptionalFieldValidationExample extends Div {

    private TextField optionalEmailField = new TextField("可选邮箱");
    private TextField requiredNameField = new TextField("姓名"); // 用于演示其他字段
    private Binder<UserData> binder = new Binder<>(UserData.class);

    private static final String EMAIL_REGEX = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6}$";
    private static final String INVALID_EMAIL_FORMAT_MSG = "邮箱格式不正确";

    public OptionalFieldValidationExample() {
        // 1. 定义数据模型
        UserData userData = new UserData();
        binder.setBean(userData);

        // 2. 绑定必填字段 (示例)
        binder.forField(requiredNameField)
              .asRequired("姓名不能为空")
              .bind(UserData::getName, UserData::setName);

        // 3. 绑定可选字段并实现条件验证
        binder.forField(optionalEmailField)
              .withValidator(value -> value.isEmpty() || value.matches(EMAIL_REGEX), INVALID_EMAIL_FORMAT_MSG)
              .bind(UserData::getEmail, UserData::setEmail);

        // 4. 添加一个提交按钮来触发验证
        Button submitButton = new Button("提交", event -> {
            try {
                binder.writeBean(userData); // 尝试写入Bean，会触发所有绑定字段的验证
                Notification.show("数据有效，提交成功！" + userData.toString(), 3000, Notification.Position.MIDDLE);
            } catch (Exception e) {
                Notification.show("数据无效，请检查输入。", 3000, Notification.Position.MIDDLE);
            }
        });

        add(requiredNameField, optionalEmailField, submitButton);
    }

    // 简单的数据模型
    public static class UserData {
        private String name;
        private String email;

        public String getName() { return name; }
        public void setName(String name) { this.name = name; }
        public String getEmail() { return email; }
        public void setEmail(String email) { this.email = email; }

        @Override
        public String toString() {
            return "UserData{name='" + name + "', email='" + email + "'}";
        }
    }
}