How to create a validator that allows only input to any one field

Introduction

How to extend Bean Validation: thermometer_face:

Confirmation environment

• Development environment
• JDK 1.8
• Spring Framework 4.3
• BeanValidation 1.1
• Operating environment
• JBoss EAP 7.1

• TERASOLUNA Server Framework for Java (5.3.0.RELEASE) is used as the framework.

How to make a validator in the first place?

First, make an annotation

Mostly a copy of the code in Constraint composition: sweat:

AllowSingleInput.java

import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.validation.Constraint;
import javax.validation.Payload;

@Documented
@Constraint(validatedBy = {AllowSingleInputValidator.class}) //Class made with ↓
@Target({TYPE, ANNOTATION_TYPE}) //Allow it to be attached only to classes or annotations
@Retention(RUNTIME)
public @interface AllowSingleInput {
  String message() default "{com.neriudon.example.validator.SingleInput.message}";

  Class<?>[] groups() default {};

  Class<? extends Payload>[] payload() default {};

  String[] fields(); //Make an array

  @Target({TYPE, ANNOTATION_TYPE})
  @Retention(RUNTIME)
  @Documented
  @interface List {
    AllowSingleInput[] value();
  }
}

The point is to target the annotation only to the class or annotation, and to have an array of String in the field. You can write the message solidly, but I have set Please input to only one text filed in the properties.

Make a validator

Now, let's create a class that does the actual input check. Well, the basics are a copy of Example: sweat:

AllowSingleInputValidator.java

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import org.springframework.beans.BeanWrapper;
import org.springframework.beans.BeanWrapperImpl;
import org.springframework.util.StringUtils;

public class AllowSingleInputValidator implements ConstraintValidator<AllowSingleInput, Object> {
  private String[] fields;

  private String message;

  @Override
  public void initialize(AllowSingleInput constraintAnnotation) {
    fields = constraintAnnotation.fields(); //Get field name
    message = constraintAnnotation.message();
  }

  @Override
  public boolean isValid(Object value, ConstraintValidatorContext context) {
    BeanWrapper beanWrapper = new BeanWrapperImpl(value);
    //Process to check if any one field is entered
    boolean isSingleInput = false;
    for (String field : fields) {
      if (!StringUtils.isEmpty(beanWrapper.getPropertyValue(field))) {
        if (isSingleInput) {
          isSingleInput = false;
          break;
        } else {
          isSingleInput = true;
        }
      }
    }

    if (isSingleInput) {
      return true;
    } else {
      context.disableDefaultConstraintViolation();
      //Message output if conditions are not met
      context.buildConstraintViolationWithTemplate(message).addPropertyNode(fields[0])
          .addConstraintViolation();
      return false;
    }
  }
}

I get the target field name with ʻinitialize and check if it is entered in only one of the fields with ʻisValid (maybe there is another good way to write it: frowning2 :).

How to use

Annotate the Form class and set the field name to check the input in fields.

@AllowSingleInput(fields = {"todoTitle1", "todoTitle2", "todoTitle3"})
public class TodoForm implements Serializable {

  private static final long serialVersionUID = 1L;

  private String todoTitle1;

  private String todoTitle2;

  private String todoTitle3;

  // getter/omit setter
}

There is no need to change jsp.

<!--Extract only the Form-->
<form:form action="${pageContext.request.contextPath}/todo/create"
	method="post" modelAttribute="todoForm">
    <form:label path="todoTitle1"/>
    <form:input path="todoTitle1" />
    <form:errors path="todoTitle1" cssClass="text-error" /><br>
    <form:label path="todoTitle2"/>
    <form:input path="todoTitle2" />
    <form:errors path="todoTitle2" cssClass="text-error" /><br>
    <form:label path="todoTitle3"/>
    <form:input path="todoTitle3" />
    <form:errors path="todoTitle3" cssClass="text-error" /><br>
    <form:button>Create Todo</form:button>
</form:form>

Execution result

You can now get an error message when you fill in multiple fields and press a button: v :.

Background to this post

As a memo because I needed this validator for the project I was involved in.