"BuildUp" means not to create an object, but inject dependencies to an existing object according to annotations such as "Required". Expecting it will find proper beans for those dependencies automatically.
Related
I have a Spring Boot application with different submodules which also contains spring components.
And in the main web modules I use 70% of the beans from the submodules. It depends on the application.yml properties, if the property group (which points to a bean) is enabled or not.
First I wanted to create Aspect-s, so when a method of a bean (which is not enabled by it's property) is called, then throw an exception. This solution could work, but then I would need to create Aspect classes, method annotations, import more and more dependencies.
So I am just wondering, would be there any other easier solution to disable a bean, or do not load at all to the spring boot container?
I would imagine something like #DependsOn, but for this you need to give a name of a bean name, but you cannot use this annotation to work with yml property.
Other easy solution is to #Bean or #Import every bean I want to managed by spring container, instead of #Import everything once from submodules, but then it is a static setting, cannot be overwrite by a single property from yml.
Spring introduced the concept of conditionals quite some time ago. Spring Boot uses this to a great extend to conditionally enable features. It even created a lot of conditional rules which you can use.
One of those rules is the conditional on a property rule. To use this rule add an #ConditionalOnProperty annotation to your bean. Now it will only be included if said property is enabled or has the specific value.
#ConditionalOnProperty(name="your.property.name")
I recently learnt that in hibernate, we need a no-arg constructor in an entity because hibernate instantiates its entities via reflection:
Hibernate implementation. Are we paying the reflection penalty?
I got curious that whether it is the same case with Spring and found that Spring beans do not require a no-argument constructor mandatorily.
This brings me to the question that how does spring creates its objects if not by reflection - to which I think that Spring is a container and instantiates beans and injects dependencies on startup and it must be able to load the application beans via some classloader and hence it does not need reflection.
Then, I get back to the starting point with the question that hibernate also has my application class definition available then why does it need reflection to create its entities?
can somebody please confirm or correct my understanding and provide me an answer?
I use Play Framework + Spring Data JPA from this example:
https://github.com/typesafehub/play-spring-data-jpa
I have models, repositories and now I want to initialize my DB on start up. I inject repositories to my Global.java file using #Autowired, but they equals to null on run time. It's because Spring don't try to inject dependencies to Global.java, because Global.java don't have even package name, so I can't tell Spring to scan his package!
With controllers Spring DI works well, but how to use it in Global.java? How to initialize database using repositories?
You can change package of Global.java in application.conf by setting property application.global.
Other way can be to fetch dependency explicitly calling
context.getBean(YourBeanClass)
in Global.java instead of autowiring it, as you have context available in Global.
You may explicitly create a bean by defining it in your context xml
<bean id="global" class="Global"></bean>
Also, having classes in default packages is not a good idea.
Our application uses #Bean to define create beans and load them into the Spring context.
We now need to externalize these, so as to enable the application to be configured without touching the java source code.
We wish to replace the #Bean's with Groovy classes.
Is there a way to annotate a Groovy bean so that it will be picked up by Spring?
Note that we cannot simply reference each Groovy bean in the Spring XML, as we need to add and modify beans without touching the Spring code.
Thanks very much.
Use Spring config inheritance.
Move all shared code in a common "base" project that each individual / specific project depends on. Use Maven for this.
Create a common / base Spring config and put that into the "base" project. This config doesn't contain a definition for ProcessDefinition
In the specific project, create one bean which inherits from ProcessDefinition. Create a Spring config which imports the base config and define the single specific bean in it.
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 dependency 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.