Combine two maven based projects on two frameworks

I have two maven projects say MvnSpring and MvnGuice.MvnSpring is working on spring and hibernate frame works. And MvnGuice is working on google guice and mybatis. I need to combine both the features together. Both are following singleton pattern. I need to get some class of MvnSpring in MvnGuice while coding. So that I created a jar of MvnSpring and put it in .m2 repository and give the dependacy details in MvnGuice. Now I can import classes of MvnSpring in MvnGuice classes.MvnSpring uses spring dependency injection and MvnGuice uses guice dependency injection for object creation. Now in MvnSpring flow is MSserviceImpl(implements MSservice) > MSdaoImpl(implements MSdao). Now I need to call MSService class from MvnGuice. Then at run time it shows error like MSService class is null. Then I made a guice depende开发者_开发百科ncy injection for MSService class in MvnGuice. Now the control reaches MSserviceImpl but now MSdao is null at here. Is it possible to start MvnSpring along with MvnGuice. I hope then I can solve the issue.

---

While Spring and Guice are targeted at the same problem, IoC, they take very different approaches to solve it. They differ both in functionality and in how they are configured, where Spring has bean definitions and Guice uses bindings.

Fortunately they do have common grounds in that they both support JSR-330, a standards specification that defines a set of annotations. This enables you to write your singletons and describe the injections that they need without depending on either Spring or Guice.

This way you can share your singletons between projects irregardless of the framework you use in a particular project. I would not recommend using both Guice and Spring in the same project, except if there's a clearly defined separation between them. For instance you might use Guice for a module that is used by Spring code via a defined API that hides the fact that it internally is based on Guice.

---

There was already mentioned JSR-330. For some cases it can be not enough, e.g., you have code:

final String className = config.getProperty(«serviceImpl»);
// Class.forName(name) and check required interface for type safety
final Class<? extends Service> serviceClass = Reflection.classForName(className, Service.class);
final Service service = injector.getInstance(serviceClass);

In different DI environments you are supposed to support both com.guice.inject.Injector.getInstance() and org.springframework.context.ApplicationContext.getBean() implementations.

There is the draft solution sdif4j Simple Dependency Injection Facade. The idea of this project is to encapsulate different DI frameworks logic with own abstraction to extend default JSR-330 possibilities. Note, there is no public releases yet, but you can find ideas how to solve your problem or make an internal release in a fork. The general issue, is that your both MvnSpring and MvnGuice projects are supposed to be based on JSR-330 (instead of guice/spring annotations) and org.sdif4j:sdif4j-api (or your own abstraction; only if Injector functionality is required). It is recommended to make guice and spring dependencies optional (to compile but not export) to allow the library clients to choose the DI themselves. In your MvnCompineGuiceAndSpring you just declare sdif4j-guice or sdif4j-spring dependency (it is similar to slf4j usage) and configure your DI environment. You can find different examples in testing subproject.

Some more notes: Spring default scope is singleton, Guice - prototype (Spring terminology). So, if you want a prototype bean, you can use:

@org.springframework.context.annotation.Scope("prototype")
@javax.inject.Named
public class TestPrototype {
}

The Spring @Scope annotation should be ignored by guice even if spring does not present in your classpath. Also you have to declare all your Singleton beans with @javax.inject.Named and @javax.inject.Singleton annotation to support both Spring and Guice, like this:

@javax.inject.Named
@javax.inject.Singleton
public class TestSingleton implements ITestSingleton {
    public TestSingleton() {
    }
}

As with @Scope annotation, you can use @ImplementedBy(@ProvidedBy) guice annotations on your code (when feasible; be careful with it, in general it is not a good practice), that should be also ignored in Spring DI (in both cases if Spring exists in classpath or not).

Hope, that's clear.