Skip to main content

Spring circular dependency solution

I would like to suggest a solution of Dependency Injection which will be as much loyal as possible to the Spring IoC way and will help to overcome the circular dependency error.
This means that we will have a single class that will have a reference to all the classes which need to be injected and will be responsible for the injection.
I'll try to walk you through the steps.
Assuming we have the following service classes which cause the circular error:
@Service
public class ServiceA{
@Autowire
ServiceB serviceB;
@Autowire
ServiceC serviceC;
}
@Service
public class ServiceB{
@Autowire
ServiceA serviceA;
@Autowire
ServiceC serviceC;
}  
                                           
First step is to remove the @Autowire annotations, so we will move the wiring responsibility out of Spring hands.
Second step is to create a class which will hold a reference to all the classes to inject. Such as:


@Component
public class BeansManager{
@Autowire
private ServiceA serviceA;
@Autowire
private ServiceB serviceB;
@Autowire
private ServiceC serviceC;
get...
set...
}          
 
Third step is to create an interface name Injectable with method inject.
public interface Injectable
{
public void inject(BeansManager beansManager);
}

Forth step is to set each service class/interface to implement the injectable interface.
e.g. :

@Service
public class ServiceA implements Injectable{
ServiceB serviceB;
ServiceC serviceC;
//method to inject all the beans which were previously were injected by Spring
public void inject(BeansManager beansManager)
{
this.serviceB =  beansManager.getServiceB();
this.serviceC = beansManager.getServiceC();
}
                 
Fifth and final step is to set the BeansManager to be ready for the injection.

                                             
But take a moment to think -
It's obvious that we need  a reference of all the classes which need to be injected in the BeansManager, however, how can we make sure that the following sequence is maintained:
1. All Service classes are initiated
2. BeansManager is initiated with all the services injected by Spring
3. After BeansManager initiated and exist in its steady state, call all the service classes which need injection and inject the relevant service.

Step 3 can be achieved by a method which executed after constructor finished (via @PostConstruct annotation), however the big question here is how to make sure the BeansManager is initiated last? (after all the relevant services are initiated)

The trick is to have @Autowire on the Injectable set.

This way Spring will make sure that:
a. All the injectable classes are subscribed to the BeansManager for the injection
b. The BeansManager will be initiated last (after all injectable services are initiated)

public class BeansManager
{
//This line will guarantee the BeansManager class will be injected last
@Autowired
private Set<Injectable> injectables = new HashSet();
//This method will make sure all the injectable classes will
//get the BeansManager in its steady state,
//where it's class members are ready to be set
@PostConstruct
private void inject() {
   for (Injectable injectableItem : injectables) {
       injectableItem.inject(this);
   }
}
}

Make sure you understand all the magic that happened in the fifth step, it's really cool.



Actual Post -  http://gal-levinsky.blogspot.in/2012/04/judgement-day-weapon-for-circular.html


                                 

Comments

Popular posts from this blog

Extent report plugin for cucumber framework

Extent Reports  are the most popular  reporting  used with Selenium. ExtentReport API makes our life easy to generate interactive  report  with simple configuartions. It supports almost all Java and .NET test frameworks such as TestNG , JUnit , NUnit etc Here we are discussing about  a plugin which is build on  Extent Report specially for Cucumber. This plugin is used to simple out the implementation of  Extent Report  in  Cucumber Framework .  We are creating a maven project to implement the integration of our plugin with cucumber 1. Create new maven project in any tool eclipse/sts/intellij 2. Open pom.xml and update below entries. Step 1 : Add Cucumber Extent Reporter library to Maven Project Add  cucumber-extentsreport <dependency>      <groupId> com.vimalselvam </groupId>      <artifactId> cucumber-extentsreport </artif...

java: You aren't using a compiler supported by lombok, so lombok will not work and has been disabled.

  In order to make projects compile with the existing builds of Lombok processor, as a workaround you can use the flag -Djps.track.ap.dependencies=false which should be added to File | Settings | Build, Execution, Deployment | Compiler | Build process VM options field. This will disable collection of dependencies specified by an annotation processor when Filer methods are called

javax.servlet.ServletException: Circular view path

Problem : javax.servlet.ServletException: Circular view path [error]: would dispatch back to the current handler URL [/latestOrder] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.) Solution : You've annotated the controller method as producing JSON or String or any other object . You probably want to annotate the method with @ResponseBody and change its return type to allow you to return an object representation of the JSON that you want to include in the response Preview: @RequestMapping (value= "latestOrders" ,method = RequestMethod. GET ) public @ResponseBody List<Order> listProducts(Model model) throws JMSException{ List<Order> list= new ArrayList(); list. add (staff1) return list; }