Friday, 31 August 2012

Hibernate Validator - Creating custom constraints @Required – Example 4

In this post, we will see how we can create our own custom constraints tailored to our specific requirements.

Creating our own custom constraint is not that much complicated, it is a matter of defining two steps :
a) Create a constraint annotation
b) Create a constraint validation

I am going to explain step by step for creating our own constraint  called @Required which is the combined of @NotNull and @NotEmpty.

Now let us start.

Environment


  1. Eclipse 3.7 Indigo IDE
  2. Hibernate 4.1.1
  3. JavaSE 1.6
  4. MySQL 5.1

Step 1:
Let us set up the environment first. Follow this post to set up Hibernate with java in eclipse IDE.

Step 2:
We need to add some more jar files for Validator. Please follow the steps

  1. Right click on Project and Select Properties.
  2. Select Java Build Path.
  3. Click “Add External JARs..” and include the following jar files. (you can also download by clicking the following files)

hibernate-validator-4.0.2.GA.jar
hibernate-validator-annotation-processor-4.1.0.Final.jar
slf4j-simple-1.4.2.jar
log4j-1.2.15.jar
slf4j-api-1.4.2.jar
validation-api-1.0.0.GA.jar

Step 3
In the mysql, create the following table.


 

CREATE TABLE `validatorexample5` (
  `ID` BIGINT(20) NOT NULL AUTO_INCREMENT,
  `firstName` VARCHAR(255) DEFAULT NULL,
  PRIMARY KEY  (`ID`)
) ENGINE=INNODB DEFAULT CHARSET=latin1

Step 4
Now let us create the java bean without our constraint. Later we will come back , add our newly created custom constraint.

package domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

import myConstraints.Required;


@Entity
@Table(name = "validatorexample5")
public class validatorexample5 {

@Id
@GeneratedValue
@Column(name = "ID")
private int ID;

@Column(name = "FirstName")
private String firstName;

public int getID() {
return ID;
}

public void setID(int iD) {
ID = iD;
}

public String getFirstName() {
return firstName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

}



 


Now let us map this class in the hibernate.cfg.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost/sampledb</property>
<property name="connection.username">root</property>
<property name="connection.password">123</property>

<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>

<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>

<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>

<!-- Mapping Classes -->
<mapping class="domain.validatorexample5" />

</session-factory>
</hibernate-configuration>

Very Important, We need add one more property in the above xml file as follows
<property name="javax.persistence.validation.mode">none</property>





Now let us create our constraint annotation as follows.





package myConstraints;

import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import javax.validation.Constraint;
import javax.validation.Payload;

@Target( { METHOD, FIELD, ANNOTATION_TYPE })
@Retention(RUNTIME)
@Constraint(validatedBy = RequiredValidator.class)
@Documented
public @interface Required {

String message() default "{default message}";

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

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



}

Next, we need to implement a constraint validator, that's able to validate elements with a @RequiredValidator. To do so, we implement the interface ConstraintValidator as shown below:




package myConstraints;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

public class RequiredValidator implements ConstraintValidator<Required, String> {

public void initialize(Required constraintAnnotation) {

}

public boolean isValid(String value, ConstraintValidatorContext constraintContext) {
if (value == null) {
return false;
}
if (value instanceof String) {
String stringValue = (String) value;
if (stringValue.trim().length() == 0) {
return false;
}
}
return true;
}

}



Now, let us go back to bean and add our custom constraint as follows.


package domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

import myConstraints.Required;


@Entity
@Table(name = "validatorexample5")
public class validatorexample5 {

@Id
@GeneratedValue
@Column(name = "ID")
private int ID;

@Column(name = "FirstName")
@Required(message="First name cannot be empty or null")
private String firstName;

public int getID() {
return ID;
}

public void setID(int iD) {
ID = iD;
}

public String getFirstName() {
return firstName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

}


Now, in order to test our code, we will create our test class as follows


package test;

import java.util.Set;
import javax.validation.ConstraintViolation;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;
import org.hibernate.Session;
import HibernateUtilities.HibernateUtil;
import domain.validatorexample5;

public class Test {
public static void main(String[] args) {


validatorexample5 v1 = new validatorexample5();


ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
Validator validator = factory.getValidator();
Set<ConstraintViolation<validatorexample5>> constraintViolations = validator
.validate(v1);

// printing the results
for (ConstraintViolation<validatorexample5> constraintViolation : constraintViolations) {
System.out.println(constraintViolation.getPropertyPath() + " -> "
+ constraintViolation.getMessage());
}
Session session = HibernateUtil.beginTransaction();
session.save(v1);
HibernateUtil.CommitTransaction();

}
}


Now right click test.java and select run as Java Application. You can see the following output and shows the validation constraints.

2 [main] INFO org.hibernate.validator.util.Version - Hibernate Validator 4.0.2.GA
12 [main] INFO org.hibernate.validator.engine.resolver.DefaultTraversableResolver - Instantiated an instance of org.hibernate.validator.engine.resolver.JPATraversableResolver.
firstName -> First name cannot be empty or null
log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into validatorexample5 (FirstName) values (?)



 

That’s all


Project Structure:
image

2 comments:

  1. Wonderful, very helpful. But it appears that this would work only for String objects as coded, correct? What if the form had
    Integer age;
    defined and I wanted that to be @Required as well? Better still would rework it to work with any Object

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