Can or should a Service layer be a Spring bean?
If so, how should it be got from a calling application, a consumer of a service?
Because the consumer must be aware that such a bean exists, so it in any case must use Spring
to make use of Service methods.
Of course. The service layer is the part of your application that is visible to other users (e.g. a Web layer) so it needs to be configured and setup somewhere. Imho a Spring configuration is the best place to put this configuration in. The Service Layer user then has to take care of instantiating that context and getting the Service Objects he needs.
An alternative - if it needs to run standalone - would be for your service class(es) implementing the Service Layer interface(s) to instantiate the Spring application context themselves.
By making your consumers also spring beans, and inject the service bean with dependency injection.
Yes, It is always nice to configure service beans as spring beans. In the web layer you need to take care of instantiating the needed service objects. Another option is to make the web layer classes also as spring beans and inject the necessary service layer spring beans. From the testing point of view also, this type of design is very helpful when we use Spring testing framework.
Related
I am trying to learn Spring Framework, before that I used to create application with EJBs
[Web services]->[Business Layer]->[DAO Layer] | [Database]
in following way
WebServices: Restful API using Jersey with url mappings, that support both JSON and XML format( news/list.json, news/list.xml). Once a request is received by an endpoint(url-mapped-method) it is forwarded to a relevant EJB through lookup(remote, local). EJB process every thing, apply business rules and return result as DTO(Data transfer object),Service then transform the result into required format (JSON, XML)
Business Layer: Business Layer (Facade) implemented in EJB with remote and local interfaces, these EJBs can call other EJBs. WebService layer(and/or Timer service and MDBs) can also call any of the EJBs). For timer service related functionality I used EJB Timer Service and for Messages used Message Drive Bean and interceptor for logging and auditing.
DAO Layer: All the Database related functions(add,edit, delete, search) JPA/Hibernate using EntityManager are written here (Entity beans and HQL).
Seamless Transaction support, each EJB's method (lookup-based) call is treated as a separate transaction and calling methods of DAO layer are part of same transaction(provided that no extra configuration is provided). multiple operations are carried out in a single transaction If one db operation fails all others are roll backed automatically. Each Table is mapped as an entity class with relations etc.
I have worked on Spring MVC but could not map/understand correctly for above architecture
I know bit about AOP and that I think is a perfect replacement for Interceptors (or at least it work for me)
Now my question is how all these could be replaced in Spring framework?
Jersey (RestAPi) alternative in Spring>
EJB alternative in Spring (as EJB supports remoting, each lookup call to a method is treated as a transaction, calls to EJB's method could be intercepted and it comes with state-full and stateless flavors)?
Timer Service alternative in Spring?
Message Drive Bean alternative in Spring?
Interceptor alternative is AOP in Spring (As per my experience and that serve my purpose)
JPA(entity manager) alternative in spring?
Jersey (RestAPi) alternative in Spring?
Spring MVC does this perfectly fine, in my opinion. Just annotate your methods in your controller as the REST apis you want to use.
EJB alternative in Spring (as EJB supports remoting, each lookup call to a method is treated as a transaction, calls to EJB's method could be intercepted and it comes with state-full and stateless flavors)?
There is no full alternative. There are several techniques that implement this in parts: Spring remoting for remote calls, Spring transactions as transactions, Spring AOP interceptors for intercepting calls. However, for example XA transactions on remote calls are something you don't get as such in Spring. Spring however works fine with EJBs, so if you prefer them, you can still have them and use Spring in other parts of your software.
Timer Service alternative in Spring?
Spring task scheduling
Message Drive Bean alternative in Spring?
Message Listener Containers
Interceptor alternative is AOP in Spring (As per my experience and that serve my purpose)
There are several levels of interceptors in spring. There are handler interceptors in mvc, there are bean call interceptors like the SpringAutowiringInterceptor, and there are AOP-based interceptors that can be used in multiple layers.
JPA(entity manager) alternative in spring?
Spring has multiple of these as well. It's actually quite straightforward to just use JPA with Spring-Data, it's designed to integrate to JPA. There are Spring JDBC and other data layer alternatives though if Spring Data is not what you want.
Jersey (RestAPi) alternative in Spring ⇨ it's rest api (in spring with #Path annotation) or spring mvc if you want to use controllers (#Controller annotation)!
EJB alternative in Spring ⇨ Spring doesn't give statefull bean out of a box but you can use #Service annotation (or #Repository for DAO) but you have to handle transactions manually (with annotations for example)
Message Drive Bean alternative ⇨ There is no equivalent out of the box in Spring, you could use injection and librairies of Spring to get it working (package org.springframework.jms should contains what you need)!
JPA(entity manager) alternative is not ejb ⇨ so it can be used in Spring.
Spring is a lighweight library so you can do all you do with EJB but it's more configurable so you will have more work to do the same that EJB do. But this configuration brings you some advantages: you have the hand on it!
This explains Spring and Java EE (which is what you would have used EJBs in) side by side: http://www.slideshare.net/reza_rahman/java-ee-and-spring-sidebyside-34320697
Jersey offers Spring solutions too - see their website
Spring does support remote calls through, e.g., RMI; It also supports transactions; AFAIK, no explicit stateful/stateless Spring Components - it depends on how you use it
AFAIK nothing as awesome as TimerService, however, you could use Quartz
Spring offers MDPs (Message-Driven POJOs)
Spring does support JPA - see first link.
Another cool comparison slideshare: http://www.slideshare.net/kelapure/java-e-evsspringshootout
I am trying to understand how to best make use of spring application context hierarchies. Assuming I have an Application where I have #Controller beans, #Service beans, and #Repository beans, representing a front-end, business and persistence layer, it would seem nice if the layers had contexts in which only beans are visible which are relevant to the context. It would also be nice if I did not need special code for creating beans, just using #Autowired should be enough.
I can create a context for my repositories, let's say repoContext, in which there exist only the repository beans. The service layers needs access to those, but not vice versa, so I'd might create another context serviceContext which has repoContext as parent. Now the front-end layer needs the services, so I might create a controllerContext with serviceContext as parent. But doing so, the controllerContext would also be able to deliver repository beans to the front-end layer, which is the opposite of what I wanted.
So it seems to me that to properly separate bean dependencies in separate contexts, the parent-child relationship is not very useful to provide dependencies to a context.
Is there any better way? Could there be a front-end and a backend context sharing configuration of the service beans, but with the backend context being resposible to insatntiate service beans first (because only this context has repositories)? Or would that approach lead to the frontend context trying to instantiate own service beans?
Is it possible to inject a bean from a web application that deploy in another server!
I declare a scenario to myself, I have two web application that use spring framework and deploy separately in different application servers (one is TOMCAT and another one is WEBLOGIC),the first application has ServiceA and the second one has ServiceB, now I want to inject ServiceB in ServieA?
I try to do this with RMI once an another one with JMS, now I am wondering that:
Is it possible with another thing?
Is there any active project about this scenario exist?
How can share application context in spring framework, is it possible?
Thanks.
Bean is just an object in JVM. You certainly cannot use an object from one JVM in another JVM straightforward.
But you can do 2 things:
Use proxies - some objects that will have the same interface but invoke somehow to the proper server as implementation.
Use service-oriented architecture (SOA). Each server should have some limited set of beans that are responsible for their functionality. And all beans can interact with each other.
Maybe OSGI is suitable for this.
Web services, JAX-RS is the simplest. But JAX-WS provides you with the tools to automatically generate the client code.
I know that the general consensus is to use one or the other, but we have a specific task where we would like to use our spring services from within a stateless ejb timer.
Is there a standard way of getting a spring service from outside the normal flow of my web app? (Note I'm using the stripes framework and it has built in spring support and I'm using this built in support to access my spring services normally)
According to the Spring manual you can configure an EJB 3 injection interceptor that will take care of injecting #Autowired springbeans into your EJB Session Beans.
I am using Spring to manage my DAO & Services. And JSF for UI. I want to use dependency injection in my JSF backing-bean. There is an article that explained how I can do that.
But I have two separate projects: one for Service and one for UI. The Spring configuration file is located in Service project.
How can I connect both project with Spring? I want to annotate my JSF pages for DI.
You can achieve this by using Spring Web Flow.
Spring have examples which show:
A JSF centric approach where your Spring and JSF beans are managed/configured the JSF way (faces-config) and a
Spring centric approach where your beans (including ManagedBeans) are managed in the Spring Context.
See Spring Flow Web Home
If you mean that you have one WAR with web services defined in it, and another separate WAR with the JSF stuff, I think it's really two separate projects each with their own Spring configuration.
The web service WAR will use either Spring web services or perhaps HTTP remoting to expose your service interfaces to clients via HTTP. This will have one set of application context configuration, either XML or annotations.
The JSF WAR will have the JSPs and controllers. The controllers will be injected with clients that will interact with the remote services to accomplish what you wish. That's all they need to know about the service WAR. There doesn't need to be any duplication of configuration at all.
It's actually a nice design, because it completely decouples the view from the rest of the problem.
Thank for everyone I did it. My mistake was with bean initialization. I tried to access my injected bean in constructor, but must must did in #PostConstruct method. And all that time i tried to find mistake in my config file. But it was in such simply place :)
I find some solution one:
Sample Application using JSF, Spring 2.5, and Java Persistence APIs with Glassfish v2
. But I have problem with it.
I can post this problem hear or must create new topic? Sorry for stupid question, i'm newbie her.