How to use CDI qualifiers with multiple class implementations? - jsf

I'm new in Java EE/JSF and now read about CDI qualifiers - the possibility to change class implementation. This is great but I have got one question. As far as I understand I can change class implementation using qualifier but I need to change it everywhere I use this implementation. What is the best solution to do it in one place? With my small knowledge about Java EE I figured out this one.
Lets imagine that we are creating simple Calculator application. We need to create few classes:
Calculator (basic implementation of calculator)
ScientificCalculator (scientific implementation of calculator)
MiniCalculator (with minimum potentiality)
MockCalculator (for unit tests)
Qualifier #Calculator (will indicate to the actual implementation of calculator; should I create qualifier for each implementation?)
Here is the question. I've got four implementations of calculator and I want to use one of them in few places but only one at time (in the initial project phase I will use MiniCalculator, then Calculator and so on). How can I change implementation without change code in every place where object is injected? Should I create factory which will be responsible for injecting and will work as method injector? Is my solution correct and meaningful?
Factory
#ApplicationScoped
public class CalculatorFctory implements Serializable {
private Calculator calc;
#Produces #Calculator Calculator getCalculator() {
return new Calculator();
}
}
Class which uses Calculator
public class CalculateUserAge {
#Calculator
#Inject
private Calculator calc;
}
Is this the correct solution? Please correct me if I'm wrong or if there is a better solution. Thanks!.

There are several issues here.
What is the best way to change the desired implementation in the entire application? Look into #Alternatives.
Do I need a qualifier for each implementation? No, see this answer for a lengthy and detailed explanation.
Should I use a producer to decide which implementation is injected? Could be the solution you want, but I doubt it. Producers are generally used to perform some sort of initialization that can't be done in the constructor / #PostConstruct. You could also use it to inspect the injection point and make runtime decisions about what to inject. See the link 2. for some clues.
Is this solution correct? This will work, but you'll still have to mess with the code to change the implementation, so consider 1. first. Also #Calculator Calculator seems highly redundant. Again, see the link at 2.
#ApplicationScoped
public class CalculatorFctory implements Serializable {
private Calculator calc;
#Produces #Calculator Calculator getCalculator() {
return new Calculator();
}
}
Update:
CDI uses qualifiers in addition to types for dependency resolution. In other words, as long as there is only one type that matches the type of the injection point, types alone are enough and qualifiers are not needed. Qualifiers are there for disambiguation when types alone are not enough.
For example:
public class ImplOne implements MyInterface {
...
}
public class ImplTwo implements MyInterface {
...
}
To be able to inject either implementation, you don't need any qualifiers:
#Inject ImplOne bean;
or
#Inject ImplTwo bean;
That's why I say #Calculator Calculator is redundant. If you define a qualifier for each implementation, you're not gaining much, might as well just use the type. Say, two qualifiers #QualOne and #QualTwo:
#Inject #QualOne ImplOne bean;
and
#Inject #QualTwo ImplTwo bean;
The example directly above does not gain anything since in the previous example no dis-ambiguity existed already.
Sure, you can do this for cases where you don't have access to particular implementation types:
#Inject #QualOne MyInterface bean; // to inject TypeOne
and
#Inject #QualTwo MyInterface bean; // to inject TypeTwo
However OP shouldn't be using #Produces when he wants Calculator implementations to be CDI managed.
#Avinash Singh - CDI manages #Produces as well as anything they return, as long as it is CDI that calls the method. See this section of the spec if you please. This includes returning `#...Scoped beans which will support dependency injection, life-cycle callbacks, etc.
I overlooked some details here, so consider the following two:
public class SomeProducer {
#Inject ImplOne implOne;
#Inject ImplTwo implTwo;
#Inject ImplThree implThree;
#Produces
public MyInterface get() {
if (conditionOne()) {
return implOne;
} else if (conditionTwo()) {
return implTwo;
} else {
return implThree;
}
}
}
and
public class SomeProducer {
#Produces
public MyInterface get() {
if (conditionOne()) {
return new ImplOne();
} else if (conditionTwo()) {
return new ImplTwo();
} else {
return new ImplThree;
}
}
}
Then, in the first example, CDI will manage the life cycle (i.e. #PostConstruct and #Inject support) of what's returned from the producer, but in the second one it will not.
Back to the original question - what's the best way to switch between implementations without having to modify the source? The assumption is that you want the change to be application wide.
#Default
public class ImplOne implements MyInterface {
...
}
#Alternative
public class ImplTwo implements MyInterface {
...
}
#Alternative
public class ImplThree implements MyInterface {
...
}
Then, any for any #Inject MyInterface instance, ImplOne will be injected, unless
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/beans_1_0.xsd">
<alternatives>
<class>ImplTwo</class>
</alternatives>
</beans>
is specified, in which case ImplTwo will be injected everywhere.
Further Update
There are indeed things in the Java EE environment that are not managed by CDI, such as EJBs and web services.
How would you inject a web service into a CDI managed bean? It's simple really:
#WebServiceRef(lookup="java:app/service/PaymentService")
PaymentService paymentService;
That's it, there you'll have a valid reference to the payment service which is managed outside CDI.
But, what if you didn't want to use the full #WebServiceRef(lookup="java:app/service/PaymentService") everywhere you need it? What if you only want to inject it by type? Then you do this somewhere:
#Produces #WebServiceRef(lookup="java:app/service/PaymentService")
PaymentService paymentService;
and in any CDI bean that needs a reference to that payment service you can simply #Inject it using CDI like this:
#Inject PaymentService paymentService;
Note that before defining the producer field, PaymentService wouldn't be available for injection the CDI way. But it is always available the old way. Also, in either case the web service is not managed by CDI but defining the producer field simply makes that web service reference available for injection the CDI way.

If you want to swap the implementation in your code using a factory method then your factory method is managing the beans and not CDI and so there is really no need for #Calculator.
#ApplicationScoped
public class CalculatorFactory implements Serializable {
enum CalculatorType{MiniCaculator,ScientificCaculator,MockCalculator};
Calculator getCalculator(CalculatorType calctype) {
switch(calctype)
case MiniCaculator : return new MiniCalculator();
case ScientificCalculator : new ScientificCalculator();
case MockCalculator : new MockCalculator();
default:return null;
}
}
public class CalculatorScientificImpl {
private Calculator calc =
CalculatorFactory.getCaclulator(CaclutorType.ScientificCalculator);
doStuff(){}
}
public class CalculatorTest {
private Calculator calc =
CalculatorFactory.getCaclulator(CaclutorType.MockCalculator);
doStuff(){}
}
However if you want your Caclulator beans to be CDI managed for injections and life cycle management using #PostConstruct etc then you can use one of the below approaches.
Approach 1 :
Advantage :You can avoid creating annotation using #Named("miniCalculator")
Disadvantage : compiler will not give an error with this approach if there is a name change from say miniCalculator to xyzCalculator.
#Named("miniCalculator")
class MiniCalculator implements Calculator{ ... }
#ApplicationScoped
public class CalculatorFactory implements Serializable {
private calc;
#Inject
void setCalculator(#Named("miniCalculator") Caclulator calc) {
this.calc = calc;
}
}
Approach 2 : Recommended (Compiler keeps track of injection if any injection fails)
#Qualifier
#Retention(RUNTIME)
#Target({FIELD, TYPE, METHOD})
public #interface MiniCalculator{
}
#ApplicationScoped
public class CalculatorFactory implements Serializable {
private calc;
#Inject
void setCalculator(#MiniCalculator calc) {
this.calc = calc;
}
}
Approach 3: If you are using a factory method to generate your object.Its lifecycle wont be managed be CDI but the Injection will work fine using #Inject .
#ApplicationScoped
public class CalculatorFactory implements Serializable {
private Calculator calc;
#Produces Calculator getCalculator() {
return new Calculator();
}
}
public class CalculateUserAge {
#Inject
private Calculator calc;
}
All three approaches will work for testing , say you have a class named CaculatorTest,
class ScientificCalculatorTest{
Caclulator scientificCalculator;
#Inject
private void setScientificCalculator(#ScientificCalculator calc) {
this.scientificCalculator = calc;
}
#Test
public void testScientificAddition(int a,int b){
scientificCalculator.add(a,b);
....
}
}
if you want to use a mock implementation in your test then do something like this,
class CalculatorTest{
Caclulator calc;
#PostConstruct
init() {
this.calc = createMockCaclulator();
}
#Test
public void testAddition(int a,int b){
calc.add(a,b);
.....
}
}

Related

CDI injection of subclasses of session scoped beans as a managed property

I am using JSF 2.3 and I want to inject different sublaccess of a session scoped bean as a managed property using CDI.
From the link below
How to inject different subclasses as ManagedProperty JSF 2?
I understood that this was not possible for RequestScoped beans using the "old" JSF and JEE-annotations, but my beans have session scope and I am using CDI injection, and therefore different annotations than the ones used in the above link.
In particular I do have:
public abstract class BaseContainer {
String prop1;
}
#Named
#SessionScoped
public class MaklerContainer extends BaseContainer {
String prop 2;
}
#Named
#SessionScoped
public class AppManagerContainer extends MaklerContainer {
String prop 3;
}
public abstract class BaseBean {
#Inject
#javax.faces.annotation.ManagedProperty(value = "#{maklerSessionContainer}")
private MaklerSessionContainer maklerSessionContainer;
}
Is it possible to inject interchangeably instances of both MaklerContainer and AppManagerContainer as a managed property maklerSessionContainer of the class BaseBean above?
Let me describe one option, there may be others.
First of all, if you want to inject different sublaccess, you have to find a way to disambiguate them for CDI, or it will complain about "Ambiguous dependencies". E.g. given the class hierarchy of the question, the line below results in ambiguous dependency exception, because CDI cannot decide whether to inject the MaklerContainer or the AppManagerContainer that extends it:
#Inject MaklerContainer maklerContainer; // ambiguous!
You can use qualifiers, named beans, or #Typed (perhaps there are even more ways).
Let's use #Named, since it is already present.
The idea is to create a producer that introduces a third bean of type MaklerContainer, with a different name, to the appropriate scope. The producer code will decide which of the 2 implementations to choose at runtime. Something like this:
#ApplicationScoped
public class TheProducer {
#Inject #Named("maklerContainer")
private MaklerContainer maklerContainer;
#Inject #Named("appManagerContainer")
private AppManagerContainer appManagerContainer;
#Inject
private User currentUser;
#Produces
#SessionScoped
#Named("theOne") // choose appropriate name of course
public MaklerContainer makeMaklerContainer() {
if (currentUser.hasRole("Role1")) {
return appManagerContainer;
} else {
return maklerContainer;
}
}
}
Now all you have to do is inject the appropriate named MaklerContainer, like:
#Inject #Named("theOne") MaklerContainer maklerContainer;

Extending PartialViewContext with a RequestScoped bean in JSF

In a JSF project, we wrote our own PartialViewContext to listen to some events fired by pages beans:
#RequestScoped
public class OurPartialViewContext extends PartialViewContextWrapper
{
...
// called by cdi
#SuppressWarnings("unused")
private void listenForUpdate(#Observes OurRefreshEvent event)
{
...
And we wrote the matching factory, injecting it:
public class OurPartialViewContextFactory extends PartialViewContextFactory
{
#Inject
private OurPartialViewContext customPartialViewContext;
...
Problem is that in the newest versions of JSF, the empty constructor for PartialViewContextWrapper is deprecated, asking us to use another constructor with the wrapped object in parameter.
Currently, our PartialViewContext needs to be tied to the request scope, in order to be modified during the request by the observed events and to be used by a custom PartialResponseWriter we also wrote.
So our PartialViewContext currently both:
must have an empty constructor, as it is a #RequestScoped bean;
should not have an empty constructor, as it is deprecated for PartialViewContextWrapper which it inherits from.
How could we find a solution there?
We tried to remove it from the scope and build it in the Factory with a simple new OurPartialViewContext(), but then the #Observes methods are never called.
You are required to pass the wrapped instance into the constructor and to use getWrapped() over all place in delegate methods. Otherwise your application will most probably not work when you install other JSF libraries which also ship with their own PartialViewContext implementation such as OmniFaces and PrimeFaces. You would be effectively completely skipping the functionality of their PartialViewContext implementation. This mistake was previously observed in too many custom implementations of factory-provided classes. Hence the urge to mark the default constructor as #Deprecated so that the developers are forced to use the proper design pattern.
Your specific issue can be solved by simply refactoring the listenForUpdate() method into a fullworthy request scoped CDI bean, which you then inject in the factory who in turn ultimately passes it into the constructor of your PartialViewContext implementation.
Thus, so:
#RequestScoped
public class OurEventObserver {
public void listenForUpdate(#Observes OurRefreshEvent event) {
// ...
}
}
public class OurPartialViewContextFactory extends PartialViewContextFactory {
#Inject
private OurEventObserver observer;
public OurPartialViewContextFactory(PartialViewContextFactory wrapped) {
super(wrapped);
}
#Override
public PartialViewContext getPartialViewContext(FacesContext context) {
PartialViewContext wrapped = getWrapped().getPartialViewContext(context);
return new OurPartialViewContext(wrapped, observer);
}
}
public class OurPartialViewContext extends PartialViewContextWrapper {
private OurEventObserver observer;
public OurPartialViewContext(PartialViewContext wrapped, OurEventObserver observer) {
super(wrapped);
this.observer = observer;
}
// ...
}
Inside any of the overridden methods of OurPartialViewContext you can simply access the state of the observer, provided that the listenForUpdate() modifies some instance variables representing the state.

CDI #Specializes and Constructor Injection with #Postconstruct

I have the following classes:
#Named
#ViewScoped
public class BaseClass {
private SomeDependency dep;
public BaseClass(){}
#Inject
public BaseClass(SomeDependency dep) {
this.dep = dep;
}
#PostConstruct
private void initialize() {
dep.doSomething(); // Point "A"
}
public String getProperty() {
return "BaseClass-Property";
}
#Specializes
public class SpecialClass extends BaseClass() {
#Override
public String getProperty() {
return "SpecialClass-Property";
}
}
Now in some .xhtml I have something like
<h:outputText value="#{baseClass.property}" />
This works fine without the SpecialClass. It breaks with a NullPointerException at Point "A" if I include the SpecialClass in the project.
Well, according to the Weld specification, this is more or less intended behavior:
When an enabled bean specializes another bean, the other bean is never
instantiated or called by the container.
Nevertheless, now I have to make sure that every #Specializes bean implements the complete constructor like
public SpecialClass() {}
#Inject
public SpecialClass(SomeDependency dep) { super(dep); }
which IMHO is kind of counter-intuitive and produces a lot of duplicated, boilerplate code, especially with something like 5-6 arguments for every constructor. Also, this is never caught when creating a new specialized bean since the project is always still compile clean.
Am I doing something wrong or is there no alternative to implementing the constructors over and over again?
BTW, I do use Constructor Injection to create easily testable classes where I can just use the constructor to "Inject" dummy implementations of the dependencies.
CDI 1.1 spec at section 4.3 says:
"The only way one bean can completely override a second bean at all
injection points is if it implements all the bean types and declares
all the qualifiers of the second bean."
Your base class is annotated with the Named qualifier and the specializing class is not. You should also mark it with Alternative and enable it in beans.xml. There's also the ViewScoped annotation. Unless it's the Omnifaces' ViewScoped, it looks like you're mixing up JSF managed beans with CDI beans.

Dependency injection in abstract and concrete classes

I'm using JSF and am running in a problem for quite awhile, I've searched at a lot of places but couldn't find any suitable answer.
Can I have dependency injection working in an abstract (or more generally a class higher in the hierarchy) class ?
Also, how should we handle annotations when working with inheritance ? I've read that the common practice would be not to annotate the abstract class, only the concrete one, but then, it would imply no injection for that abstract ?
My problem is that one (check the last comment) :
Abstract class
#ManagedBean
#ViewScoped
public abstract class AbstractController<T extends VersionedObject> implements Serializable {
#ManagedProperty("#{libraryVersionController}")
private LibraryVersionController libraryVersionController;
public List<T> loadFromDatasource(IVersionedServiceBase<T> service) {
log.info("Loading generic VO from data source");
VersionedObjectFilter filter = new VersionedObjectFilter();
filter.setSelectedLibVersion(libraryVersionController.getSelectedItem());
// etc
}
// getters, setters...
}
Concrete class
#ManagedBean
#ViewScoped
public class DomainController extends AbstractController<Domain> implements Serializable {
private List<Domain> allItems;
private Domain[] selectedItem;
#ManagedProperty(value = "#{domainService}")
private DomainService domainService;
#PostConstruct
public void loadFromDatasource() {
allItems = super.loadFromDatasource(domainService);
// !! DOES NOT WORK, null pointer exception on abstract class (libraryVersionController)
// etc
}
Getters and setters are correctly set up, as I could read in my .xhml it is the concrete class that I'm referencing (#{domainController.allItems}), there is only one #PostConstruct. I'm using JSF2.1 and Mojarra.
Thanks for your help !
As to your NullPointerException, my guess is that AbstractController.setLibraryVersionController is missing. As I understand it, when the AbstractController is constructed (presumably it has an implicit constructor even though it's abstract), that method is needed to fill in the appropriate value.
I know you said all getters and setters are there, but this one seems tricky, so possibly you missed it. If you add logging to this method, you can check that JSF is attempting to fill in the value, and also check whether the value is null or not.
On the general question of how dependency injection works with the inheritance hierarchy, I would guess that your approach is OK, and that dependencies are injected for the base class and then for the derived class, down the chain.

managed bean EJB injection

i'm having many managed beans and was wondering if i could create a UtilClass where i
put my services calls (#EJB). I've already tried it but i'm having a NullPointerException.
this is how my UtilClass and my managed bean look like:
public class UtilClass{
#EJB
private static MyFirstEjbLocal myFirstService;
#EJB
private static MySecondEjbLocal mySecondService;
//other services
//getters
}
public class MyManagedBean{
public String myMethod(){
UtilClass.getMyFirstService.doSomethingInDB();
return null;
}
}
I would suggest you to do the following, since apparently you are having a lot of services and want to have them grouped together, you can create an "abstract" bean and make your managed bean extend such "abstract" bean, in this way you can access the EJB's in a structural and safe way, the following code will explain what I mean:
public class MyAbstractBean{
#EJB
protected MyFirstEjbLocal myFirstService;
#EJB
protected MySecondEjbLocal mySecondService;
// All your other EJB's here
...
// All other variables and methods you could need
}
public class MyManagedBean
extends MyAbstractBean{
public String myMethod1(){
myFirstService.doSomethingInDB();
return "";
}
public String myMethod2(){
mySecondService.doSomethingInDB();
return "";
}
}
Please refer to JavaEE5 EJB FAQ if you need to clarify more concepts on the matter.

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