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.

Now we can define the actual constraint annotation. If you've never designed an annotation before, this may look a bit scary, but actually it's not that hard: It is a matter of writing some boiler plate code and filling in the blanks.

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:

Read More

Hibernate Validator - Creating custom constraints–Example

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 by taking hibernate documentation example as here..
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 `validatorexample4` (
  `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;

@Entity
@Table(name = "validatorexample4")
public class validatorexample4 {

    @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.validatorexample4" />

    </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.

First we need a way to express the two case modes. We might use String constants, but a better way to go is to use a Java 5 enum for that purpose:

package myConstraints;

public enum CaseMode {
    UPPER, LOWER;
}

Now we can define the actual constraint annotation. If you've never designed an annotation before, this may look a bit scary, but actually it's not that hard: It is a matter of writing some boiler plate code and filling in the blanks.

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 = CheckCaseValidator.class)
@Documented
public @interface CheckCase {

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

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

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

}

• The annotation interface has three mandatory attributes: message, groups and payload


• @Target({ METHOD, FIELD, ANNOTATION_TYPE }): Says, that methods, fields and annotation declarations may be annotated with @CheckCase (but not type declarations e.g.)


• @Retention(RUNTIME): Specifies, that annotations of this type will be available at runtime by the means of reflection


• @Constraint(validatedBy = CheckCaseValidator.class): Specifies the validator to be used to validate elements annotated with @CheckCase


• @Documented: Says, that the use of @CheckCase will be contained in the JavaDoc of elements annotated with i

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

package myConstraints;

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

public class CheckCaseValidator implements ConstraintValidator<CheckCase, String> {

    private CaseMode caseMode;

    public void initialize(CheckCase constraintAnnotation) {
        this.caseMode = constraintAnnotation.value();
    }

    public boolean isValid(String object, ConstraintValidatorContext constraintContext) {

        if (object == null)
            return true;
        
        boolean isValid;
        if (caseMode == CaseMode.UPPER) {
            isValid = object.equals(object.toUpperCase());
        }
        else {
            isValid = object.equals(object.toLowerCase());
        }
        
        return isValid;
    }

}

The ConstraintValidator interface defines two type parameters, which we set in our implementation. The first one specifies the annotation type to be validated (in our example CheckCase), the second one the type of elements, which the validator can handle (here String).

In case a constraint annotation is allowed at elements of different types, a ConstraintValidator for each allowed type has to be implemented and registered at the constraint annotation as shown above.

The implementation of the validator is straightforward. The initialize() method gives us access to the attribute values of the annotation to be validated. In the example we store the CaseMode in a field of the validator for further usage.

In the isValid() method we implement the logic, that determines, whether a String is valid according to a given @CheckCase annotation or not. This decision depends on the case mode retrieved in initialize(). As the Bean Validation specification recommends, we consider null values as being valid. If null is not a valid value for an element, it should be annotated with @NotNull explicitly.

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.CaseMode;
import myConstraints.CheckCase;

@Entity
@Table(name = "validatorexample4")
public class validatorexample4 {

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

    @Column(name = "FirstName")
    @CheckCase(value = CaseMode.UPPER, message="First Name should be in upper case") 
    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.validatorexample4;

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

         
        validatorexample4 v1 = new validatorexample4();
        v1.setFirstName("a");
        
        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        Validator validator = factory.getValidator();
        Set<ConstraintViolation<validatorexample4>> constraintViolations = validator
                .validate(v1);

        // printing the results
        for (ConstraintViolation<validatorexample4> 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
13 [main] INFO org.hibernate.validator.engine.resolver.DefaultTraversableResolver - Instantiated an instance of org.hibernate.validator.engine.resolver.JPATraversableResolver.
firstName -> First Name should be in upper case
log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into validatorexample4 (FirstName) values (?)

That’s all

Project Structure:

Read More

Hibernate Validator Example 2

In this example, we will see some more validation constraints such as @email, @past, @length, etc. And also we will also define custom error message.

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 the environment. 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.

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 `validatorexample3` (
  `ID` BIGINT(20) NOT NULL AUTO_INCREMENT,
  `FirstName` VARCHAR(255) DEFAULT NULL,
  `LastName` VARCHAR(255) DEFAULT NULL,
  `BirthDate` DATE DEFAULT NULL,
  `CustomerNumber` VARCHAR(255) DEFAULT NULL,
  `SSN` VARCHAR(255) DEFAULT NULL,
  `Email` VARCHAR(255) DEFAULT NULL,
  `zip` VARCHAR(255) DEFAULT NULL,
  PRIMARY KEY  (`ID`)
) ENGINE=INNODB DEFAULT CHARSET=latin1

 

Step 4

Now let us create the java bean for the above table.

package domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Past;
import javax.validation.constraints.Pattern;
import javax.validation.constraints.Size;
import java.util.Date;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import org.hibernate.validator.constraints.Length;
import org.hibernate.validator.constraints.NotEmpty;

@Entity
@Table(name = "validatorexample3")
public class validatorexample3 {

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

    @NotNull(message="First name cannot be empty")
    @Size(min = 2,message="First name is too small")
    @Column(name = "FirstName")
    private String firstName;

    @Length(min = 2, max = 50, message="LastName should be 2 to 50 Characters size")
    @Column(name = "LastName")
    private String lastName;

    @Column(name = "BirthDate")
    @Temporal(TemporalType.DATE)
    @Past(message="Date of birth should be past date")
    private Date birthDate;
    
    @Pattern(regexp = "^[a-zA-Z]{2}-\\d+$", message="Invalid Customer Number")
    @Column(name = "CustomerNumber")
    private String customerNumber;

    @Pattern(regexp= "[0-9]{3}-[0-9]{2}-[0-9]{4}",   message="Invalid SSN format")
    @Column(name = "ssn")
    private String ssn;

    @Column(name = "Email")
    @org.hibernate.validator.constraints.Email(message="Invalid Email Format")
    private String Email;

    @NotEmpty
    @Length(min = 5, max = 5, message = "{zip.length}")
    @Pattern(regexp = "[0-9]+", message="Invalid Zip")
    @Column(name = "zip")
    private String zip;
     
    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;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Date getBirthDate() {
        return birthDate;
    }

    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }

    public String getCustomerNumber() {
        return customerNumber;
    }

    public void setCustomerNumber(String customerNumber) {
        this.customerNumber = customerNumber;
    }

    public String getSsn() {
        return ssn;
    }

    public void setSsn(String ssn) {
        this.ssn = ssn;
    }

    public String getEmail() {
        return Email;
    }

    public void setEmail(String email) {
        Email = email;
    }

    public String getZip() {
        return zip;
    }

    public void setZip(String zip) {
        this.zip = zip;
    }


}

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.validatorexample3" />

    </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 add our test class.

package test;


import java.text.SimpleDateFormat;
import java.util.Date;
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.validatorexample3;

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

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); 
         
        validatorexample3 v1 = new validatorexample3();
        v1.setFirstName("a");
        v1.setLastName("012345678900123456789001234567890012345678900123456789001234567890");
        v1.setBirthDate(sdf.parse(sdf.format(new Date())+1));
        v1.setCustomerNumber("#@3434");
        v1.setSsn("3fdfdfdf");
        v1.setEmail("asdasdasdsadsad");
        v1.setZip("asdasdsadasd");
        
        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        Validator validator = factory.getValidator();
        Set<ConstraintViolation<validatorexample3>> constraintViolations = validator
                .validate(v1);

        // printing the results
        for (ConstraintViolation<validatorexample3> 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 default message.

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.
Email -> Invalid Email Format
lastName -> LastName should be 2 to 50 Characters size
birthDate -> Date of birth should be past date
zip -> {zip.length}
zip -> Invalid Zip
firstName -> First name is too small
ssn -> Invalid SSN format
customerNumber -> Invalid Customer Number
log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into validatorexample3 (Email, BirthDate, CustomerNumber, FirstName, LastName, ssn, zip) values (?, ?, ?, ?, ?, ?, ?)

That’s all.

Project Structure

Read More

Hibernate Validator Examples

Let us some examples for Hibernate validator
Here is the introduction notes from the hibernate documentation

Bean Validation standardizes how to define and declare domain model level constraints. You can, for example, express that a property should never be null, that the account balance should be strictly positive, etc. These domain model constraints are declared in the bean itself by annotating its properties. Bean Validation can then read them and check for constraint violations. The validation mechanism can be executed in different layers in your application without having to duplicate any of these rules (presentation layer, data access layer). Following the DRY principle, Bean Validation and its reference implementation Hibernate Validator has been designed for that purpose.

The integration between Hibernate and Bean Validation works at two levels. First, it is able to check in-memory instances of a class for constraint violations. Second, it can apply the constraints to the Hibernate metamodel and incorporate them into the generated database schema.

Each constraint annotation is associated to a validator implementation responsible for checking the constraint on the entity instance. A validator can also (optionally) apply the constraint to the Hibernate metamodel, allowing Hibernate to generate DDL that expresses the constraint. With the appropriate event listener, you can execute the checking operation on inserts, updates and deletes done by Hibernate.

When checking instances at runtime, Hibernate Validator returns information about constraint violations in a set of ConstraintViolations. Among other information, the ConstraintViolation contains an error description message that can embed the parameter values bundle with the annotation (eg. size limit), and message strings that may be externalized to a ResourceBundle.

Example 1:
In the first example, we will see very basic not null constraint validation. Here is the Step by Step Tutorial.

Example 2:
In the second example, we will see some more constraint validation. Here is the Step by Step Tutorial.

Example 3:
In this example, we will see how we can create our custom constraint validation. Here is the Step by Step Tutorial.

Example 4:
In this example, we will see how we can create our custom constraint @Required. Here is the Step by Step Tutorial.

Example 5:
In this example, nothing is new, we will take care example 2 and will use the utility class to perform validation. Here is the Step by Step Tutorial.

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Hibernate Validator Example 1

In this example, we will see very basic validation @NotNull.

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 the environment. 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.

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 `validatorexample1` (
  `ID` BIGINT(20) NOT NULL AUTO_INCREMENT,
  `FirstName` VARCHAR(255) DEFAULT NULL,
  `LastName` VARCHAR(255) DEFAULT NULL,
  `MiddleName` VARCHAR(255) DEFAULT NULL,
  PRIMARY KEY  (`ID`)
) ENGINE=INNODB DEFAULT CHARSET=latin1

Step 4

Now let us create the java bean for the above table.

package domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.validation.constraints.NotNull;

@Entity
@Table(name = "validatorexample1")
public class validatorexample1 {

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

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

    @Column(name = "LastName")
    @NotNull
    private String lastName;

    @Column(name = "middleName")
    private String middleName;

    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;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getMiddleName() {
        return middleName;
    }

    public void setMiddleName(String middleName) {
        this.middleName = middleName;
    }

}

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.validatorexample1" />

    </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 add our test class.

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 domain.*;
import HibernateUtilities.*;

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

        validatorexample1 v1 = new validatorexample1();
        v1.setFirstName("John");
        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        Validator validator = factory.getValidator();
        Set<ConstraintViolation<validatorexample1>> constraintViolations = validator
                .validate(v1);

        // printing the results
        for (ConstraintViolation<validatorexample1> 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 default message.

2 [main] INFO org.hibernate.validator.util.Version - Hibernate Validator 4.0.2.GA
13 [main] INFO org.hibernate.validator.engine.resolver.DefaultTraversableResolver - Instantiated an instance of org.hibernate.validator.engine.resolver.JPATraversableResolver.
lastName -> may not be nulllog4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into validatorexample1 (FirstName, LastName, middleName) values (?, ?, ?)

That’s all.

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