JValidate, a validation library

JValidate is a library for validating javabeans. Java annotations or XDoclet-tags are used define validation rules for properties of javabeans. A validation engine validates the javabeans. Furthermore it provides utility classes to propagate and transform validation messages to the user interface.Several, web-framework specific, components are included to present the validation messages.

JValidate solves a problem that many (web) developers faces. We want to define our validation once and only once, and by preference not in the UI. Further, we do not want to depend on whatever validation mechanism the web-framework is using.

With JValidate we tried to create a generic validation engine, which requires no coupling to validation code in the javabeans itself. Other design goals of JValidate are

We strived for simplicity and ease of use for the developer in defining the validation rules. Consistency in defining these rules once and only once and consistency in the mechanism used to validate and presentation of validation messages.

Try JValidate yourself to see if we succeeded in accomplishing these goals!

First download and install the required libraries. You can download the JValidate jars from the sourceforge site. Which libraries you need is depending of which JDK and which web-framework, if any, you are using. JValidate consists of the following libraries.

JValidate is using a set of third party libraries.

The second step is defining your validation rules. If you are using JDK 1.5, you can use java annotations, otherwise you have to use xdoclet tags.

Section 2.1 describes how to use annotations, section 2.2 describes how to use XDoclet tags. For both section's we define a customer and an address javabean, for which we define the validation rules.

...
        
  @ValidateClass 
  public class Customer {
        
  ...

  }        
        

...

  @ValidateIsNotBlank
  public String getFirstName() {
        return firstName;
  }
...

...

  @ValidateIsNotBlank
  @ValidateMaxLength(length=20)
  public String getFirstName() {
        return firstName;
  }

...

  @ValidateIsNotBlank(errorCode="firstname.isrequired")
  @ValidateMaxLength(length=20, errorCode="firstname.tolong")
  public String getFirstName() {
        return firstName;
  }

...  

 @ValidateClass 
 public class Address{
     
   ...
   
  @ValidatePattern(pattern="^[1-9]\\d{3}[- ]?[a-zA-Z]{2}$", errorCode="invalid.zipcode")
  public String getZipCode() {
      return zipCode;
  }
  
  ...

 }

...

  @ValidateIsValid
  @ValidateIsRequired 
  public Address getAddress() {
        return address;
  }
...

...
        
/**
 * @validate.class
 * 
 */
public class Customer{

...

}        
        

...

 /**
   * @validate.isnotblank
   * 
   * @param firstName The firstName to set.
   * @return Returns the firstName.
  */
   public String getFirstName() {
     return firstName;
   }

...

...

  /**
   * @validate.isnotblank
   * @validate.maxlength value="20"
   * 
   * @param firstName The firstName to set.
   * @return Returns the firstName.
  */
   public String getFirstName() {
     return firstName;
   }

...

 
...

  /**
   * @validate.isnotblank errorcode="firstname.isrequired"
   * @validate.maxlength value="20" errorcode="firstname.tolong"
   * 
   * @return Returns the firstName.
   */
   public String getFirstName() {
     return firstName;
   }

...

...  


/**
 * @validate.class
 * 
 */
public class Address{
     
...

  /**
   * @validate.pattern value="^[1-9]\\d{3}[- ]?[a-zA-Z]{2}$" errorcode="zipcode.invalidformat"
   *
   * @return Returns the zipcode.
   */
    public String getZipCode() {
      return zipCode;
   }
  
...

  }

...
public class Customer{

   ...

  /**
   * 
   * @validate.isvalid
   * @validate.isrequired 
   * 
   * @return Returns the Address.
   */
   public Address getAddress() {
        return address;
  }
...

...



<taskdef name="validates" classname="xdoclet.modules.knowlogy.validation.ValidationDocletTask" >
    <classpath>
       <path refid="validate.classpath"/>
    </classpath>
</taskdef>


<target name="create.validation">
  <mkdir dir="${basedir}/target/java/generated" />
  <validates destdir="${basedir}/target/java/generated" force="true" verbose="true">
      <fileset dir="${basedir}/src/test/java" includes="**/*.java"/>
      <validate/>
  </validates>
</target>

This section explains how validations can be junit tested. Its also introduces us with the ValidationEngine and Messages class and illustrates their use. So lets continue.

Now were done with adding the validation rules we create a JUnit test to check our validations.

public class CustomerValidationTest extends TestCase {

    
    public void testValidateFirstName(){
        
        Customer customer = new Customer();
        
        Messages messages = new MessagesImpl();        
        ValidationEngine.validate(customer, messages);
        
        Message firstNameMessage = messages.getMessage(customer, "firstName");
        
        assertNotNull("expected a first name validtion message ",firstNameMessage);
        assertEquals("expected a firstname.isrequired errorcode","firstname.isrequired", firstNameMessage.getMessageCode());
        
        customer.setFirstName("a-name-which-is-longer-then-20-chars");
        
        messages.clear();        
        ValidationEngine.validate(customer, messages);
        firstNameMessage = messages.getMessage(customer, "firstName");
        
        assertNotNull("expected a first name validation message", firstNameMessage);
        assertEquals("expected a firstname.tolong errorcode","firstname.tolong", firstNameMessage.getMessageCode());
        
        customer.setFirstName("Adrian");
        
        messages.clear();        
        ValidationEngine.validate(customer, messages);
        firstNameMessage = messages.getMessage(customer, "firstName");
        assertNull("expected no validation message for firstname",firstNameMessage);
        
        
    }
}

Our JUnit test shows how to test the validation of the firstname of the customer. We create an instance of Customer that we gone validate. With ValidationEngine.validate the customer object is validated, along with the customer instance goes a Messages instance. The ValidationEngine validates the customer object and add validation messages, if any, to the messages object.

We can retrieve the validation message for a specific object and a specific property with the getMessage method. In the test we retrieve the message for the firstname property.

In this section we describe how we to propagate the messages back to the front-end. There are of course serveral types of front-ends, for a number of specif front-end frameworks we provide utility classes and components to integrate with those frameworks.

class CustomerService{


    public void saveCustomer(Customer customer)throws ValidateException{
      
       Validators.validate(customer);
       
       customerDao.saveCustomer(customer);
    }
       
}

class CustomerController{



   public String saveAction(){

       String outcome = "ok";
       try{
         customerService.saveCustomer(customer); 
       }catch(ValidationException ve){
         FacesContext ctx = FacesContext.getCurrentInstance();
         MessagesUtil.convert(ctx, ve.getMessages());
         outcome = "";
       }
       return outcome;
   }

}

Its possible to add validations to the defined validations. There are two possible strategies. Which one you choose depends on what you want to validate.