I am migrating from org.apache.felix.scr annotations to org.osgi.service.component annotations. I have a set of Components that inherit from a common abstract class. In the felix case, I can use a #Component annotation with the option componentAbstract=true on the super class, and then use #Reference annotation in the super class. I cannot find how to migrate this to osgi annotations.
Is it possible to use Component annotations in a super class of a Component? And if so, what is then the appropriate way to handle the properties and metatype generation?
So, what I am looking for, is something like this
/* No component definition should be generated for the parent, as it is
abstract and cannot be instantiated */
#Component(property="parent.property=parentValue")
public abstract class Parent {
#Reference
protected Service aService;
protected activate(Map<String,Object> props) {
System.out.println("I have my parent property: "+props.get("parent.property"));
#Override
public abstract void doSomething();
}
/* For this class, the proper Component definition should be generated, also
including the information coming from the annotations in the parent */
#Component(property="child.property=childValue")
public class Child extends Parent {
#Activate
public activate(Map<String,Object> props) {
super.activate(props);
System.out.println("I have my child property: "+props.get("child.property"));
}
public void doSomething() {
aService.doSomething();
}
}
By default BND will not process DS annotations in parent classes. You can change that with -dsannotations-options: inherit but please see http://enroute.osgi.org/faq/ds-inheritance.html why you shouldn't!
2021-02-23 UPDATE: It seems like the page mentioned above is no longer available. I don't know if it was moved elsewhere or simply removed but its content (in Markdown format) is still available on GitHub: https://github.com/osgi/osgi.enroute.site/blob/pre-R7/_faq/ds-inheritance.md
Related
Often people ask AspectJ questions like this one, so I want to answer it in a place I can easily link to later.
I have this marker annotation:
package de.scrum_master.app;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
#Inherited
#Retention(RetentionPolicy.RUNTIME)
public #interface Marker {}
Now I annotate an interface and/or methods like this:
package de.scrum_master.app;
#Marker
public interface MyInterface {
void one();
#Marker void two();
}
Here is a little driver application which also implements the interface:
package de.scrum_master.app;
public class Application implements MyInterface {
#Override
public void one() {}
#Override
public void two() {}
public static void main(String[] args) {
Application application = new Application();
application.one();
application.two();
}
}
Now when I define this aspect, I expect that it gets triggered
for each constructor execution of an annotated class and
for each execution of an annotated method.
package de.scrum_master.aspect;
import de.scrum_master.app.Marker;
public aspect MarkerAnnotationInterceptor {
after() : execution((#Marker *).new(..)) && !within(MarkerAnnotationInterceptor) {
System.out.println(thisJoinPoint);
}
after() : execution(#Marker * *(..)) && !within(MarkerAnnotationInterceptor) {
System.out.println(thisJoinPoint);
}
}
Unfortunately the aspect prints nothing, just as if class Application and method two() did not have any #Marker annotation. Why does AspectJ not intercept them?
The problem here is not AspectJ but the JVM. In Java, annotations on
interfaces,
methods or
other annotations
are never inherited by
implementing classes,
overriding methods or
classes using annotated annotations.
Annotation inheritance only works from classes to subclasses, but only if the annotation type used in the superclass bears the meta annotation #Inherited, see JDK JavaDoc.
AspectJ is a JVM language and thus works within the JVM's limitations. There is no general solution for this problem, but for specific interfaces or methods you wish to emulate annotation inheritance for, you can use a workaround like this:
package de.scrum_master.aspect;
import de.scrum_master.app.Marker;
import de.scrum_master.app.MyInterface;
/**
* It is a known JVM limitation that annotations are never inherited from interface
* to implementing class or from method to overriding method, see explanation in
* JDK API.
* <p>
* Here is a little AspectJ trick which does it manually.
*
*/
public aspect MarkerAnnotationInheritor {
// Implementing classes should inherit marker annotation
declare #type: MyInterface+ : #Marker;
// Overriding methods 'two' should inherit marker annotation
declare #method : void MyInterface+.two() : #Marker;
}
Please note: With this aspect in place, you can remove the (literal) annotations from the interface and from the annotated method because AspectJ's ITD (inter-type definition) mechanics adds them back to the interface plus to all implementing/overriding classes/methods.
Now the console log when running the Application says:
execution(de.scrum_master.app.Application())
execution(void de.scrum_master.app.Application.two())
By the way, you could also embed the aspect right into the interface so as to have everything in one place. Just be careful to rename MyInterface.java to MyInterface.aj in order to help the AspectJ compiler to recognise that it has to do some work here.
package de.scrum_master.app;
public interface MyInterface {
void one();
void two();
// Cannot omit 'static' here due to https://bugs.eclipse.org/bugs/show_bug.cgi?id=571104
public static aspect MarkerAnnotationInheritor {
// Implementing classes should inherit marker annotation
declare #type: MyInterface+ : #Marker;
// Overriding methods 'two' should inherit marker annotation
declare #method : void MyInterface+.two() : #Marker;
}
}
Update 2021-02-11: Someone suggested an edit to the latter solution, saying that the aspect MarkerAnnotationInheritor nested inside interface MyInterface is implicitly public static, so the modifiers in the aspect declaration could be omitted. In principle this is true, because members (methods, nested classes) of interfaces are always public by default and a non-static inner class definition would not make sense inside an interface either (there is no instance to bind it to). I like to be explicit in my sample code, though, because not all Java developers might know these details.
Furthermore, currently the AspectJ compiler in version 1.9.6 throws an error if we omit static. I have just created AspectJ issue #571104 for this problem.
I have classes:
#Creatable
#Singleton
public class Sample1 implements ISample {
}
#Creatable
#Singleton
public class Sample2 implements ISample {
}
How can i get all beans of type ISample from EclipseContext?
The Eclipse context does not support anything like this. All you can do is look for objects with a specific name (or specific class which is just converted to a name).
Additionally objects declared using #Creatable are not even created and added to the context until something actually uses them.
Dagger 1's plus() method is something I used quite often in previous applications, so I understand situations where you might want to have a subcomponent with full access to the parent graphs bindings.
In what situation would it be beneficial to use a component dependency instead of a subcomponent dependency and why?
Component dependencies - Use this when you want to keep two components independent.
Subcomponents - Use this when you want to keep two components coupled.
I will use the below example to explain Component dependencies and Subcomponents. Some points worth noticing about the example are:
SomeClassA1 can be created without any dependency. ModuleA provides and instance of SomeClassA1 via the provideSomeClassA1() method.
SomeClassB1 cannot be created without SomeClassA1. ModuleB can provide an instance of SomeClassB1 only if an instance of SomeClassA1 is passed as an argument to provideSomeClassB1() method.
#Module
public class ModuleA {
#Provides
public SomeClassA1 provideSomeClassA1() {
return new SomeClassA1();
}
}
#Module
public class ModuleB {
#Provides
public SomeClassB1 provideSomeClassB1(SomeClassA1 someClassA1) {
return new SomeClassB1(someClassA1);
}
}
public class SomeClassA1 {
public SomeClassA1() {}
}
public class SomeClassB1 {
private SomeClassA1 someClassA1;
public SomeClassB1(SomeClassA1 someClassA1) {
this.someClassA1 = someClassA1;
}
}
Dagger will take care of passing the instance of SomeClassA1 as an argument to provideSomeClassB1() method on ModuleB whenever the Component/Subcomponent declaring ModuleB is initialized. We need to instruct Dagger how to fulfill the dependency. This can be done either by using Component dependency or Subcomponent.
Component dependency
Note the following points in the Component dependency example below:
ComponentB has to define the dependency via the dependencies method on #Component annotation.
ComponentA doesn't need to declare ModuleB. This keeps the two components independent.
public class ComponentDependency {
#Component(modules = ModuleA.class)
public interface ComponentA {
SomeClassA1 someClassA1();
}
#Component(modules = ModuleB.class, dependencies = ComponentA.class)
public interface ComponentB {
SomeClassB1 someClassB1();
}
public static void main(String[] args) {
ModuleA moduleA = new ModuleA();
ComponentA componentA = DaggerComponentDependency_ComponentA.builder()
.moduleA(moduleA)
.build();
ModuleB moduleB = new ModuleB();
ComponentB componentB = DaggerComponentDependency_ComponentB.builder()
.moduleB(moduleB)
.componentA(componentA)
.build();
}
}
SubComponent
Note the following points in the SubComponent example:
As ComponentB has not defined the dependency on ModuleA, it cannot live independently. It becomes dependent on the component that will provide the ModuleA. Hence it has a #Subcomponent annotation.
ComponentA has declared ModuleB via the interface method componentB(). This makes the two components coupled. In fact, ComponentB can only be initialized via ComponentA.
public class SubComponent {
#Component(modules = ModuleA.class)
public interface ComponentA {
ComponentB componentB(ModuleB moduleB);
}
#Subcomponent(modules = ModuleB.class)
public interface ComponentB {
SomeClassB1 someClassB1();
}
public static void main(String[] args) {
ModuleA moduleA = new ModuleA();
ComponentA componentA = DaggerSubComponent_ComponentA.builder()
.moduleA(moduleA)
.build();
ModuleB moduleB = new ModuleB();
ComponentB componentB = componentA.componentB(moduleB);
}
}
According to the documentation:
Component Dependency gives you access to only the bindings exposed as provision methods through component dependencies, i.e. you have access to only types which are declared in parent Component.
SubComponent gives you an access to the entire binding graph from its parent when it is declared, i.e. you have an access to all objects declared in its Modules.
Let's say, you have an ApplicationComponent containing all Android related stuff (LocationService, Resources, SharedPreference, etc). You also want to have your DataComponent where you manage things for persistence along with WebService to deal with APIs. The only thing you lack in DataComponent is Application Context which resides in ApplicationComponent. The simplest way to get a Context from DataComponent would be a dependency on ApplicationComponent. You need to be sure you have a Context explicitly declared in ApplicationComponent because you only have access to declared stuff. In this case, there is no manual work, meaning you don't need to specify Submodules in parent Component and explicitly add your submodule to a parent module like:
MySubcomponent mySubcomponent = myComponent.plus(new ChildGraphModule("child!")); // No need!
Now consider that case where you want to inject WebService from DataComponent and LocationService from ApplicationComponent into your Fragment which binds using the #Submodule plus feature above. The cool thing here is that the component you're binding to (ApplicationComponent) does not need to expose WebService nor LocationService because you have access to the entire graph right away.
Here is the code example with screenshot for more understanding of Component and SubComponent:
Component:
AppComponent contains two declarations.
AppComponent initializes into App class.
HomeActivityComponent is dependent upon AppComponent.
In HomeActivity on initialization of DaggerHomeActivityComponent, I am giving AppComponent object as a composition.
SubComponent:
AppComponent contains SubComponent or SubComponents.
AppComponent initializes into App class.
SubComponent doesn’t know about his ParentComponent. That only providing its own dependencies by including Module.
In HomeActivity I am injecting SubComponent by using its Parent Component.
And the Pictorial Diagram:
Source: link
One other thing that I didn't quite realize until now is that:
A #Subcomponent instance has exactly one parent component (although different components can instantiate that same #Subcomponent and be that instance's parent)
A #Component may have zero, one, or many "parent" components declared through component dependencies
It seems Guice is ignoring my #Provider methods of my module.
I have a class MyModule like this:
public class MyModule extends AbstractModule {
protected void configure() {
bindInterceptor(Matchers.any(), Matchers.annotatedWith(Timed.class), new GuiceEnabledLoggingInterceptor());
bind(OneClass.class).to(OneClassImpl.class);
// And more binding lines...
}
#Provides
public AnotherClassInApi provideMyClass() {
return AnotherClassInApi.getInstance();
}
// And more #Provides methods
}
Main method is
public static void main(String[] args){
ConfigHandler.getInstance().loadConfigWhenNotRunningInsideMicrocontainer();
Injector INJECTOR = Guice.createInjector(new MyModule());
// ...
}
In some other part of the project I have class AnotherClassInApi, which is a very standard singleton plus one method:
public class AnotherClassInApi {
private static final AnotherClassInApi INSTANCE = new AnotherClassInApi();
private AnotherClassInApi() { }
// ... more methods
public static AnotherClassInApi getInstance() {
return INSTANCE;
}
}
Well, I understand that should effectively bind any request for an AnotherClassInApi object to the getInstance() method, but it doesn't work. Funny thing, a breakpoint in the #Provide method is never reached while debugging, but one in the configure method is reached. It seems guice is ignoring my provider annotation, and I think I'm following exactly what Guice guide says about #Provider, so I'm already stuck.
I've been googling around, but can't find anything similar. Any help will be much appreciated.
Thanks!
The concept of Providers (and #Provides methods) is, that they are only called when actually needed. So unless you really use your Injector to create an instance that has an #Inject dependency, your Provider is not ignored, just not used (nor needed).
You can monitor all configured bindings by using "injector.getAllBindings()".
java.util.Map,Binding> getAllBindings()
Returns a snapshot
of this injector's bindings, both explicit and just-in-time. The
returned map is immutable; it contains only the bindings that were
present when getAllBindings() was invoked. Just-in-time bindings are
only present if they have been requested at least once. Subsequent
calls may return a map with additional just-in-time bindings. The
returned map does not include bindings inherited from a parent
injector, should one exist.
This method is part of the Guice SPI and is intended for use by tools
and extensions.
I want to do something like this:
#Stateless
#Path("/sensors/{sensorid}/version")
#Consumes({MediaType.APPLICATION_XML, MediaType.TEXT_XML})
#Produces({MediaType.APPLICATION_XML, MediaType.TEXT_XML})
public class SensorVersionRestView extends VersionRestView{
#PathParam("sensorid")
private String sensorid;
#GET
#Path("count")
// so the complete path is i.e.
// domain.com/rs/sensors/111211/version/count
public void getCount() {
// do something with the sensorId....
}
}
But the only thing I get is null on runtime (I use Glassfish v3 with Jersey). The compiler and eclipse never mentions a problem with the #PathParam at the member class variable.
What's wrong with my construct?
The main problem is, why I doesn't want to use the whole path on each method in this class, that there exists another class which handles some rest operations on the sensor layer (deomain.com/rs/sensors/count i.e.)
I believe you need to change it to this:
#Stateless
#Path("/sensors/{sensorid}/version")
public class SensorVersionRestView extends VersionRestView {
#GET
#Path("count")
#Consumes({MediaType.APPLICATION_XML, MediaType.TEXT_XML})
#Produces({MediaType.APPLICATION_XML, MediaType.TEXT_XML})
// domain.com/rs/sensors/111211/version/count
public void getCount(#PathParam("sensorid") String sensorid) {
// do something with the sensorId....
}
}
Because injection occurs at object
creation time, use of this annotation
on resource class fields and bean
properties is only supported for the
default per-request resource class
lifecycle. Resource classes using
other lifecycles should only use this
annotation on resource method
parameters. - JSR-311 Javadocs
You should be able to annotate fields with #PathParam as long as the resource class lifecyle is per-request. By default the life-cycle of root resource classes is per-request.
EDIT: I don't think you can achieve this using EJBs. If you remove the #Stateless annotation, it should work.