I Have a Source class which has a dependency Of type Application Context. Using this we are achieving polymorphism. How to unit test this class. I'm using Spring boot application.
#Autowired
ApplicationContext applicationContext;
String beanName= "employeeImpl";
applicationContext.getBean(beanName, Employee.class);
For situations where you are trying to mock a hard-to-mock class, consider using a wrapper class (i.e. the Adapter/Wrapper pattern). For example, one might create new class, ApplicationContextAdapter that is auto wired into your class under test as a class that is easy to mock. This new class would internally autowire the actual ApplicationContextinstance and might have a getApplicationContext() method to get the wrapped instance.
That being said, I agree with #DarrenForsythe that you don’t shouldn’t autowire this class.
Related
This should happen quite often:
RestController -> SomeClass -> SomeOtherClass -> YetAnotherClass and so on...
In my specific case there is a chain of responsibility which is injected to a rest controller. Each class is injected to it's previous class in the above chain.
I have implemented this with spring boot and I'm trying to test the REST resource. I want to Mock the "YetAnotherClass" so that when I send a request with MockMvc I can verify that something has happened in the mock object.
The problem is if I use #MockBean to mock YetAnotherClass then I have to inject it to SomeOtherClass. I have tried to inject it with #TestConfiguration but it seems that the Mock object injection doesn't work this way when the request is sent through MockMvc and the mock object is nested deep inside a chain such as above. (The original bean is injected not the mock one)
I know that JMockit mocks every instance of a class so it would solve my problem. But Spring boot defaults to Mockito and I prefer to avoid inconsistencies.
How can I implement such a test scenario?
I've run into a lot of annoyance using Mockito's annotation config setup when setting up Spring JUnit text fixtures.
I've found the way I like mocking beans with external integrations like this this by essentially having a separate MockObjectsConfig class with the mock objects I want using the standard Spring Context Configuration, and then import it alongside my real test config:
#Configuration
public class MockObjectsConfig {
#Bean
public YetAnotherClass yetAnotherClass() {
Mockito.mock(YetAnotherClass.class); // and add any thenReturns, answers, etc. here
}
... More mock beans...
}
Then include it in your test like so:
#RunWith(SpringRunner.class)
#ContextConfiguration(classes = { MyRealConfigClass.class, MockObjectsConfig.class)
public class MyJunitTest {
#Autowired
private RestController restController;
}
You can also annotate your mock bean with #Profile and test with #ActiveProfiles if you need to prevent a conflict there.
This way your mock YetAnotherClass will get injected into your context like all your other beans -- no relying on, mixing, and fiddling around with Mockito and other library annotations.
I have a spring managed application in which I like for my service layer to be mocked. So I created a Spring Application Java Config and returned a mock of the actual service.
For e.g,
#Bean
#Profile("resource")
public MyService mockService() {
return mock(MyService.class)
}
And then the MyService goes as
class MyService {
#Autowired
private MyDao dao;
}
When Spring creates bean of name "mockService", it also tries to Autowire MyDao on the mock ? This in my opinion defeats the purpose of mocking. Is this the expected behaviour, whats the workaround ?
So bottomline, its best practice to code to interfaces rather than concrete classes particularly if you are wanting to write focused tests on specific layers.
Well, I suppose you're trying to execute an integration test, but using some mocks, doing something like this:
#RunWith(SpringJUnit4ClassRunner.class)
#SpringApplicationConfiguration(classes = {Application.class, YourMockConfigurationClass.class})
#WebIntegrationTest
public class MyIntegrationTest {
...
}
In this case, you can create a mock of your service, and tell spring that this service instance has priority:
#Bean
#Primary
public MyService mockService() {
return mock(MyService.class)
}
Doing this, whenever Spring has to inject an unqualified MyService instance, it always chooses your mock. But it doesn't prevent Spring to create the original service.
So inside Spring context there will be two instances of MyService, the mock instance and the original implementation. But using #Primary you're telling Spring that your mock has priority.
On the other hand, in order to prevent Spring to load any mock in your environments (dev, test, etc...), you should annotate your mock configuration class either with a testing #Profile or a custom annotation (like #MockBean) and then configure your component scan strategy to not load this class (#ComponentScan(excludeFilters=#Filter(MockBean.class)))
I'm currently trying to configure Spring Boot (using Java Annotations and ComponentScan) for the following scenario:
Scenario
There's an interface MyService.
I want to provide a default implementation for MyService, let's call it MyDefaultService.
If the component scan detects no other implementation for MyService, Spring should instantiate MyDefaultService as a "fallback".
If there is a different implementation of MyService present, let's say MyCustomService, then that bean should always take precedence over MyDefaultService when autowiring a dependency to MyService. In that regard, MyDefaultService should be recessive (as opposed to #Primary).
Ideally, there should not need to be an additional annotation on MyCustomService to have it "override" MyDefaultService.
Ideally, no explicitly implemented factories or factory methods should be required.
Question
The question is: how do I need to annotate the MyDefaultService class in order to achieve this?
What I tried so far to solve the problem
Annotating MyDefaultService with #ConditionalOnMissingBean(MyService.class). Didn't work because MyDefaultService is never used, even if there is no other implementation of MyService.
There is an annotation called #Primarythat solves the problem. However, it needs to reside on MyCustomService, a class that I try to keep free of additional annotations. Essentially, I need the inverse annotation of #Primary on MyDefaultService. However, I couldn't find such an annotation.
Concrete use case
I am developing a service layer in one project, and a different project will implement a web UI layer on top of it. The UI project has a dependency to the service layer project. However, for certain functionalities implemented at the service layer, I need to know which user is currently logged in at the web context. So I have to define a service interface for that in the service layer project, such that it can be implemented by the UI project. However, for testing purposes in the service-layer project, I need a default implementation of that interface. Also, in case that the UI project team forgets to implement this interface, the app should not crash, but instead instantiate the fallback bean and issue a warning.
Thanks & kind regards,
Alan
I suggest writing an implementation of FactoryBean to do this. Your FactoryBean would scan the bean factory looking for beans that implement MyService, and if it finds one it returns that bean from getObject. If it doesn't, then it can instantiate MyDefaultService directly and return that. Your factory bean then gets annotated with #Primary.
So pieces like this (pseudo-code):
public class MyServiceFactory implements FactoryBean<MyService> {
ListableBeanFactory beanFactory;
public MyService getObject() {
Map beans = beanFactory.getBeansOfType(MyService.class)
if (beans.isEmpty())
return new MyDefaultService(); // plus args, obviously
else
return get_some_bean_from_the_map
}
}
and then
#Primary
#Bean
public MyServiceFactory MyServiceFactory() {
return new MyServiceFactory();
}
Spring will automatically handle the factory bean (i.e. it will make the MyService object available as a bean for injection like normal.
This solution doesn't require any special magic, and it's fairly obvious how it works. You can also handle errant cases such as multiple MyService beans being declared.
As in the title above, I am confused about pros cons between injecting applicationContext by directly #Autowired annnotation or implementing ApplicationContextAware interface in a singleton spring bean.
Which one do you prefer in which cases and why? Thanks.
Actually, both are bad. Both of them tie your application to the Spring framework, thus inverting the whole inversion-of-control concept. In an ideal world, your application should not be aware of being managed by an ApplicationContext at all.
Once you have chosen to violate this principle, it doesn't really matter how you do it. ApplicationContextAware is the legacy version that has been around at least since Version 2.0. #Autowired is a newer mechanism but they work in pretty much the same way. I'd probably go with ApplicationContextAware, because it semantically makes clear what it is about.
As #Sean Patrick Floyd says, the need of ApplicationContext is often due to a bad design. But sometimes you have no other option. In those cases I prefer the use of #Autowired because is the way I inject all other properties. So, if I use #Autowired for injecting MyRepository, why can't I use it for ApplicationContext or any other Spring bean?
I use Spring interfaces only for those things I can't do with annotations, for example BeanNameAware.
If you need to get a prototype in a singleton then you can use method injection. Basically, you create an abstract method that returns the object you need and spring will return the prototype everytime you call that method. You define the "lookup-method" in your spring config. Here are some links:
http://docs.spring.io/spring/docs/1.2.9/reference/beans.html#beans-factory-method-injection
http://java.dzone.com/articles/method-injection-spring
Since you are not extending any of the spring classes your application is always separated from the framework. Most of the cases you will not wanted to inject the ApplicationContext as it, but will need to inject the beans defined in the ApplicationContext.
The best case is always to stick to the bare minimum, until and unless you have any specific requirement and this is very simple with spring.
So either,
Annotate your beans and scan them in application context, then use #Autowire to wire them up.
Use application context to wire your bean expediencies(old xml style configs). You can use #Autowire with this approach also.
When you want to control the bean life cycle, you can read the API and customize it, but most of the time these general settings will do the job.
Here are some examples.
Spring Auto-Wiring Beans with #Autowired annotation
Spring Auto-Wiring Beans XML Style
Spring IoC container API Docs
There is no need to use ApplicationContext at all.
ObjectFactory
If you need to use prototype scoped beans in a singleton bean, inject an org.springframework.beans.factory.ObjectFactory.
For example using constructor injection:
#Service
class MyClass {
private ObjectFactory<MyDependency> myDependencyFactory;
public MyClass(ObjectFactory<MyDependency> prototypeFactory) {
myDependencyFactory = prototypeFactory;
}
}
Why
Now what's the benefit over using ApplicationContext ?
You can substitute this dependency (e.g. in a test) by simply passing a lambda (since ObjectFactory is a #FunctionalInterface) that returns a stubbed version of it.
While it is possible to stub the ApplicationContext, it is not clear in that case which beans will be looked up and need to be stubbed.
I came across an example of #Autowired:
public class EmpManager {
#Autowired
private EmpDao empDao;
}
I was curious about how the empDao get sets since there are no setter methods and it is private.
Java allows access controls on a field or method to be turned off (yes, there's a security check to pass first) via the AccessibleObject.setAccessible() method which is part of the reflection framework (both Field and Method inherit from AccessibleObject). Once the field can be discovered and written to, it's pretty trivial to do the rest of it; merely a Simple Matter Of Programming.
Java allows you to interact with private members of a class via reflection.
Check out ReflectionTestUtils, which is very handy for writing unit tests.
No need for any setter, you just have to declare the EmpDao class with the annotation #component in order that Spring identifies it as part of the components which are contained in the ApplicationContext ...
You have 2 solutions:
To manually declare your beans in the XML file applicationContext :
<bean class="package.EmpDao" />
To use automatic detection by seeting these lines in your context file:
<context:component-scan base-package="package" />
<context:annotation-config />
AND to use the spring annotation to declare the classes that your spring container will manage as components:
#Component
class EmpDao {...}
AND to annotate its reference by #Autowired:
#Component (or #Controller, or #Service...)
class myClass {
// tells the application context to inject an instance of EmpDao here
#Autowired
EmpDao empDao;
public void useMyDao()
{
empDao.method();
}
...
}
Autowiring happens by placing an instance of one bean into the desired field in an instance of another bean. Both classes should be beans, i.e. they should be defined to live in the application context.
Spring knows the existence of the beans EmpDao and MyClass and will instantiate automatically an instance of EmpDao in MyClass.
Spring uses the CGLib API to provide autowired dependency injection.
References
Usage of CGLib forum comment by Rod Johnson
3.3.1. Injecting dependencies
Pro Spring - Analyzing Spring Dependencies
Further Reading
Introduction to the Spring Framework by Rod Johnson