I am using JBoss application server 6 and using JBoss AOP aspects in my application.
An example of aspect shown below:
public class DBAspect{
public Object accessDBConnection(FieldReadInvocation invocation) {
return dbConnection;
}
public Object accessDBConnection((FieldWriteInvocation invocation) {
throw exception;
}
}
Currently, these advice methods are applied to a private variable in class say DBUsage by binding it with this aspect.
I am migrating to a new application server and it is not supporting JBoss AOP. So, how do I implement this concept.
How can I implement this behavior. Please help.
Applying field get/set pointcuts to private field does not sound like good application or aspect design to me. Maybe refactoring your application would be a better idea. Anyway, in AspectJ you can use get() and set() pointcuts in order to intercept field get/set actions. If you want to access private fields, you might need to use a privileged aspect.
AspectJ quick reference
Privileged aspects
AspectJ pointcut types (incl. get/set)
Related
I have a Quarkus application using current versions of Vaadin Flow and Quarkus (23.2.4 and 2.13.1.Final). I want to have a VaadinServiceInitListener to check access annotations on the views (#RolesAllowed(...)) using AccessAnnotationChecker. I believe annotating the implementation with #VaadinServiceEnabled
should fix this, but I need to register it in META-INF/services/com.vaadin.flow.server.VaadinServiceInitListener to have it activated. This is how to do it when not using a dependency injection framework. Then everything works as expected and I can use AccessAnnotationChecker to see if the user has access to that view, on BeforeEnterEvent.
I also notice the message Can't find any #VaadinServiceScoped bean implementing 'I18NProvider'. Cannot use CDI beans for I18N, falling back to the default behavior. on startup. Strangely, implementing I18NProvided in a class and annotating it with #VaadinServiceEnabled and #VaadinServiceScoped makes that message go away, eg. it is recognized by CDI.
Why isn't my VaadinServiceInitListener implementation recogized? Currently it is annotated with
#VaadinServiceEnabled
#VaadinServiceScoped
#Unremovable
My pom.xml include
vaadin-quarkus-extension,
quarkus-oidc,
quarkus-keycloak-authorization,
vaadin-jandex
Instead of using a listener, you can use a CDI event.
Quarkus's dependency injection solution is based on CDI, so you can use the same events. Here's an example
public class BootstrapCustomizer {
private void onServiceInit(#Observes
ServiceInitEvent serviceInitEvent) {
serviceInitEvent.addIndexHtmlRequestListener(
this::modifyBootstrapPage);
}
private void modifyBootstrapPage(
IndexHtmlResponse response) {
response.getDocument().body().append(
"<p>By CDI add-on</p>");
}
}
More information here https://vaadin.com/docs/latest/integrations/cdi/events
Team lead wants to writing some business methods inside of Entity class, such as following:
#Entity
public class SomeProcess extends SomeProcessBase implements Serializable {
#SomeInterceptor
public void start() {
//do some business logics
}
#SomeInterceptor
public void abort() {
// do some business logics
}
...
}
Can we use CDI interceptor mechanism to intercept non-contextual entity objects?
The answer is NO.
And the next direction for this is moving to BCEL.
After a few days study, i finally finished with BCEL to achieve method intercepting.
Rough Solution:
1. Using java instrument framework to transform byte code at class load time. Click Reference.
2. Transform byte code with a bytecode manipulation lib, such as ASM, Javassist, or BCEL. While transforming bytecode, manually writing target java file, and using some tool class provided by those libs to generate java code which can create byte codes from the target class file, after some encapsulation and boxing-and-unboxing and etc, then transform byte code part would be ready. BCEL provides BCELifier class to generate those java code, and the bytecode manipulation also mentioned some other tools for the other libs.
3. Try Lifecycle open source project on github.com, which provides Java based Lifecycle description language, it's kind of using Java to describe UML state machine with meta-driven style. And for method intercepting, please refer to BCELClassFileTransformer.java
4. Contact me for more help.
In my open jpa class, we have a method like this:
#Action(Action.ACTION_TYPE.CREATE)
public void createRecord(EntityObject fileStatus) {
EntityManager em = getEntityManager();
em.persist(fileStatus);
em.flush();
}
My question is with the #Action usage. I was of the impression that we use Annotations to avoid writing boilerplate code. In this particular method, what would be the boilerplate code that we would avoid by using the annotation? I think the method would look same even without the Annotation.
It's annotation used by IBM Rational Application Developer (RAD) - Related answer on IBM support page.
Annotations can be used for documenting purposes only - in that case they doesn't affect compiled code.
This one is most likely used by RAD to recognize specific JPA manager methods so it can list them in modeling tools there (this last is only mine guess).
I've try to expose to the client(gwt) an aspectJ method through gwt-rpc, but the gwt client can't find the method defined in an aspect. The class that i expose implements IsSerializable and only it's method are visible to the client interface...the method added by their aspect contrariwise no. How i can fix this? thanks in advice.
p.s. i post a little example for more clarity:
this is the class...
public class Example implements IsSerializable{
private String name;
public setName(String name){
this.name=name
}
}
and this is the aspect...
privileged aspect Example_x{
public int Example.getVersion() {
return this.version;
}
}
The Example.getVersion() method is unavailable on the client side.
TNX
This won't work, as GWT needs access to the source of any Java class that is exposed to the client side. This is necessary to compile them from Java to Javascript. If you modify your classes using AspectJ, the added methods will not be visible to the GWT compiler and therefore not to the client.
I'd say AspectJ is simply the wrong tool for this task. If you want to add some methods to existing classes you could write a (possibly generic) container class that contains an instance of Example as well as the version information from Example_x.
I am new to OSGi and came across several examples about OSGi services.
For example:
import org.osgi.framework.*;
import org.osgi.service.log.*;
public class MyActivator implements BundleActivator {
public void start(BundleContext context) throws Exception {
ServiceReference logRef =
context.getServiceReference(LogService.class.getName());
}
}
My question is, why do you use
getServiceReference(LogService.class.getName())
instead of
getServiceReference("LogService")
If you use LogService.class.getName() you have to import the Interface. This also means that you have to import the package org.osgi.services.log in your MANIFEST.MF.
Isn't that completely counterproductive if you want to reduce dependencies to push loose coupling? As far as I know one advantage of services is that the service consumer doesn't have to know the service publisher. But if you have to import one specific Interface you clearly have to know who's providing it. By only using a string like "LogService" you would not have to know that the Interface is provided by org.osgi.services.log.LogService.
What am I missing here?
Looks like you've confused implementation and interface
Using the actual interface for the name (and importing the interface , which you'll end up doing anyway) reenforces the interface contract that services are designed around. You don't care about the implemenation of a LogService but you do care about the interface. Every LogService will need to implement the same interface, hence your use of the interface to get the service. For all you know the LogService is really a wrapper around SLF4J provided by some other bundle. All you see is the interface. That's the loose coupling you're looking for. You don't have to ship the interface with every implementation. Leave the interface it's own bundle and have multiple implementations of that interface.
Side note: ServiceTracker is usually easier to use, give it a try!
Added benefits: Using the interface get the class name avoids spelling mistakes, excessive string literals, and makes refactoring much easier.
After you've gotten the ServiceReference, your next couple lines will likely involve this:
Object logSvc = content.getService(logRef)
// What can you do with logSvc now?!? It's an object, mostly useless
// Cast to the interface ... YES! Now you need to import it!
LogSerivce logger = (LogService)logSvc;
logger.log(LogService.LOG_INFO, "Interfaces are a contract between implementation and consumer/user");
If you use the LogService, you're coupled to it anyway. If you write middleware you likely get the name parameterized through some XML file or via an API. And yes, "LogService" will fail terribly, you need to use the fully qualified name: "org.osgi.service.log.LogService". Main reason to use the LogService.class.getName() pattern is to get correct renaming when you refactor your code and minimize spelling errors. The next OSGi API will very likely have:
ServiceReference<S> getServiceReference(Class<S> type)
calls to increase type safety.
Anyway, I would never use these low level API unless you develop middleware. If you actually depend on a concrete class DS is infinitely simpler, and even more when you use it with the bnd annotations (http://enroute.osgi.org/doc/217-ds.html).
#Component
class Xyz implements SomeService {
LogService log;
#Reference
void setLog( LogService log) { this.log = log; }
public void foo() { ... someservice ... }
}
If you develop middleware you get the service classes usually without knowing the actual class, via a string or class object. The OSGi API based on strings is used in those cases because it allows us to be more lazy by not creating a class loader until the last moment in time. I think the biggest mistake we made in OSGi 12 years ago is not to include the DS concepts in the core ... :-(
You cannot use value "LogService"
as a class name to get ServiceReference, because you have to use fully qualified class name
"org.osgi.services.log.LogService".
If you import package this way:
org.osgi.services.log;resolution:=optional
and you use ServiceTracker to track services in BundleActivator.start() method I suggest to use "org.osgi.services.log.LogService" instead of LogService.class.getName() on ServiceTracker initializazion. In this case you'll not get NoClassDefFoundError/ClassNotFountException on bundle start.
As basszero mentioned you should consider to use ServiceTracker. It is fairly easy to use and also supports a much better programming pattern. You must never assume that a ServiceReference you got sometime in the past is still valid. The service the ServiceReference points to might have gone away. The ServiceTracker will automatically notify you when a service is registered or unregistered.