This page only shows a simple message from the backing bean (the call to the bean produces the bean’s initialization).
Backing Bean
import javax.annotation.PostConstruct;
import javax.enterprise.context.RequestScoped;
import javax.enterprise.event.Event;
import javax.inject.Inject;
import javax.inject.Named;
@Named
@RequestScoped
public class Controller {
@Inject
private Event<LoggerEvent> event;
private String message = "CDI Events Example";
@PostConstruct
public void init() {
event.fire(new LoggerEvent("Hello from CDI events"));
}
public String getMessage() {
return message;
}
}
Here we Inject an event (LoggerEvent) via CDI Inject annotation. Then inside the init method annotated with PostConstruct we fire the event with a new instance of the event. This is the simplest way to fire a CDI event. No matter who are listening to this event will be notified.
A simple Logger Event Handler
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.ejb.Stateless;
import javax.enterprise.event.Observes;
@Stateless
public class LoggerEventHandler {
public void log(@Observes LoggerEvent event) {
Logger.getLogger("LoggerEventHandler.class").log(Level.INFO, event.getMessage());
}
}
This class will listen for events annotated with the keyword @Observes. Because of this, it will execute the method. In this case it will print to the console a log message passed to the constructor of the event instance when it was created: Hello from CDI events as you can see in the next picture.
Result (console result) cdi events
AS you can see, it’s just that simple to create a CDi event and listen to it. This technique uses the Observer design pattern here with the help of @Observes annotation.
Feel free to comment. Download the souce code CDIEvents.
This is a simple JSF page with two date inputs and a submit button. When we press the button a the validation process will start via the backing bean that call a super class method.
Backing Bean:
@Named
@RequestScoped
public class SimpleDateRangeController extends AbstractController {
private SimpleDateRangeDto dto;
@PostConstruct
public void init() {
dto = new SimpleDateRangeDto();
}
public SimpleDateRangeController() {
}
public void action() {
super.validate(dto);
}
// getters and setters
}
</pre>
Note that in line 3 we have the super class named: AbstractController. In line 16, in the action method, we call a validate method and we pass as a parameter the dto wich has the data itself.
Abstract Controller
public class AbstractController implements Serializable {
protected <T extends DateRangeValidation> void validate(T dto) {
dto.validate();
}
}
In this abstract class we simple call the validate() method in the received DTO.
Data Transfer Object(DTO):
@ValidDateRange(endDesc = "end date", startDesc = "start date")
public class SimpleDateRangeDto extends DateRangeValidation {
private Date startDate;
private Date endDate;
// getters and setters
}
Here is the point where we annotate at the class-level with our special annotation. We simple use the annotation with 2 parameters. This parameters are optional and it’s purpose is only to personalize the error message. In case that your date fields are different from those in this example you must provide the annotation with more parameters, as you will see in the next class.
Here is where the magic happens. I will not discuss how annotations work, but I will cover the essential part: the constraint validation. The inner class DateIntervalValidator is responsible for the validation of the date fields with the help of reflection. We get the get methods of the two date fields and then we verify if endDate is after startDate. If that condition is false, we return false, otherwise we return true.
The message is required if you want personalize your message.
The start is required if your first date field is different from startDate. It indicates the name of the first field.
The end is required if your end date field is different from endDate. It indicates the name of the second date field.
The purpose the startDesc and endDesc is to use as a placeholder in the message parameter.
Validator:
public abstract class DateRangeValidation implements Serializable {
private static final long serialVersionUID = 7083856980011157895L;
public void validate() {
ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();
Validator validator = validatorFactory.getValidator();
Set<ConstraintViolation<DateRangeValidation>> result = validator.validate(this);
if (!result.isEmpty()) {
Iterator<ConstraintViolation<DateRangeValidation>> it = result.iterator();
while (it.hasNext()) {
String mesg = it.next().getMessage();
FacesContext.getCurrentInstance().addMessage(null, new FacesMessage(FacesMessage.SEVERITY_ERROR, mesg, mesg));
}
FacesContext.getCurrentInstance().validationFailed();
}
}
}
This class is the trigger of all the validation process. When in the DTO we call the validate method, is this method we are calling, because this class is the superclass of the DTO. It calls the annotation and validates the fields. If there are any erros it will collect them in a set, here called as result. Then we iterate all over the set and add the error messages to faces context.
The next few files demonstrate the same logic applied to 2 or more groups of date validations.
@Named
@RequestScoped
public class MultipleDateRangeController extends AbstractController {
private MultipleDateRangeDto dto;
@PostConstruct
public void init() {
dto = new MultipleDateRangeDto();
}
public MultipleDateRangeController() {
}
public void action() {
super.validate(dto);
}
// getters and setters
}
DTO:
@ValidDateRange.List({
@ValidDateRange(start = "date1", end = "date2", message = "{end} must be after {start}"),
@ValidDateRange(start = "date3", end = "date4", message = "{end} must be after {start}")
})
public class MultipleDateRangeDto extends DateRangeValidation {
private Date date1;
private Date date2;
private Date date3;
private Date date4;
// getters and setters
}
Plase feel free to comment or to suggest new features.
You can read more about this topic here
Download source code.
Thanks.
package staticbinder;
class Animal {
static void talk() { System.out.println("Animal doesen't talk!!"); }
void eat() { System.out.println("Animal eating..."); }
}
class Dog extends Animal {
static void talk() { System.out.println("Dog barking..."); }
@Override
void eat() { System.out.println("Dog eating..."); }
}
public class Main {
public static void main(String[] args) {
Animal a = new Dog();
/* static binding happens in private, final, static and
* overloaded methods at compile time
*/
a.talk(); // will print: Animal doesen't talk!!
/* dynamic binding happens in overriding methods at
* run time
*/
a.eat(); // will print: Dog eating...
}
}
This is not actually a new app. This is in update to an existing app that I have forgot the signing key password. So, as I’m not able anymore to update the other app, I’ve decided to publish this new one.
Of course I apologise for all of this but it’s nothing more I can do…
Please comment or suggest new features. Thanks in advance and I hope you comprehend…
Have you already tried the new amazing features of this app?
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Olá a todos! Cá estamos nós para mais uma rubrica que pretende divulgar as apps desenvolvidas pelos nossos leitores. Fiquem atentos aos fantásticos trabalhos que temos para vos mostrar e, já sabem que se quiserem ver aqui a vossa app, enviem-nos um email para: [email protected]
I want to thank you all that followed the cup with us. And of course a big and special thanks to PPLWARE because they have suggested our app today in their blog …which is a great honour to us!
Tomorrow I will deploy a new version with some improvements. Today was the first real test of the app in production, so tomorrow naturally will be a new version with some fixes detected today during the first match.
