Okay so I have been trying to get into IoC lately. However, I keep running into one hurdle - that is the fact that I love using mock objects.
They are quick and painless to setup.
However, if I use IoC all over the place in my code then it forces me to create test implementations (and configurations) of my objects instead of using mock objects (ie. using moq).
The end result is that I end up with enormous configuration files for testing.
In addition there are many scenarios in testing where I require different behaviors out of my classes on a test-to-test basis. With moq objects this is extremely easy. How would you do something similar with IoC?
Any help would be much appreciated.
Thanks,
Mike
IoC should make using mock objects easier, not harder.
Several IoC Container frameworks will allow you to define pre-existing objects to inject; with Moq you'd just set it up for myMockObject.Object.
EDIT: Example of configuring Unity with a mock:
var mockService = new Mock<IMyService>();
container.RegisterInstance<IMyService>(mockService.Object);
As an alternative, you can just pass the mock object into the constructor of the class under test (for constructor injection) and bypass the IoC container entirely in your unit tests.
EDIT: Josh's answer is a good example of the alternative. I would generally go with his solution rather than reconfiguring the container.
I love IoC, and I love me some Mock Objects...
There is no conflict with these two. If you are doing any kind of Dependency Injection then you should simply have to create mock objects using your favorite mocking framework and then pass them into your SUT.
[Test]
public void AnAwesomeTest()
{
IDependencyOne d1 = MyMocker.Create<IDependencyOne>();
IDependencyTwo d2 = MyMocker.Create<IDependencyTwo>();
//Constructor injection
SUT sut = new SUT(d1);
//Property Injection
sut.DependantProperty = d2;
//Do some stuff and Assert
}
Related
In a Spring Boot Web Application layout, I have defined a Service Interface named ApplicationUserService. An implementation called ApplicationUserServiceImpl implements all the methods present in ApplicationUserService.
Now, I have a Controller called ApplicationUserController that calls all the methods of ApplicationUserServiceImpl under different #GetMapping annotations.
As suggested by my instructor, I have defined a Dependency Injection as follows:
public class ApplicationUserController {
private final ApplicationUserService applicationUserService; //This variable will work as an object now.
public ApplicationUserController(ApplicationUserService applicationUserService) {
this.applicationUserService = applicationUserService;
}
#GetMapping
//REST OF THE CODE
}
I am new to Spring Boot and I tried understanding Dependency Injection in plain English and I understood how it works. I understood that the basic idea is to separate the dependency from the usage. But I am totally confused about how this works in my case.
My Questions:
Here ApplicationUserService is an Interface and it's implementation has various methods defined. In the code above, applicationUserService now has access to every method from ApplicationUserServiceImpl. How did that happen?
I want to know how the Object creation works here.
Could you tell me the difference between not using DI and using DI in this case?
Answers
The interface layer is used for abstraction of the code it will be really helpfull when you want to provide different implementations for it. When you create a instance you are simply creating a ApplicationUserServiceImpl and assigning it into a reference variable of ApplicationUserService this concept is called upcasting. Even though you have created the object of child class/implementation class you can only access the property or methods defined in parent class/interface class. Please refer this for more info
https://stackoverflow.com/questions/62599259/purpose-of-service-interface-class-in-spring-boot#:~:text=There%20are%20various%20reasons%20why,you%20can%20create%20test%20stubs.
in this example when a applicationusercontroller object is created. The spring engine(or ioc container) will create a object of ApplicationUserServiceImpl (since there is a single implementation of the interface ) and returns to controller object as a constructor orgument which you assign to the refrence variable also refer the concept called IOC(Invertion of control)
as explained in the previous answer the spring will take care of object creation (object lifecycle)rather than you explsitly doing it. it will make the objects loosely coupled. In this the controll of creating the instances is with spring .
The non DI way of doing this is
private ApplicationUserService applicationUserService = new ApplicationUserServiceImpl()
Hope I have answered your questions
this analogy may make you understand better consider an example, wherein you have the ability to cook. According to the IoC principle(principal which is the basis of DI), you can invert the control, so instead of you cooking food, you can just directly order from outside, wherein you receive food at your doorstep. Thus the process of food delivered to you at your doorstep is called the Inversion of Control.
You do not have to cook yourself, instead, you can order the food and let a delivery executive, deliver the food for you. In this way, you do not have to take care of the additional responsibilities and just focus on the main work.
Now, that you know the principle behind Dependency Injection, let me take you through the types of Dependency Injection
I am trying to understand the idea of spring beans and why I should use them. If I create a bean and use it to print something out like this.
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Account acc = (Account)context.getBean("account");
acc.printAccName();
Why not just create an object of that class like this
Account acc2 = new Account();
acc.printAccName();
I have been watching some video's and did some reading but I did not get an answer why it is better.
Usually what you inject is business logic or services which typically is what changes in a system.
You are trying to inject a domain object Account these objects are not subject to change so it is okay to create the object via new. Perhaps, this is what it is confusing you.
The idea, is to let the container handle the instantiation of your logic or services that change regularly so you can swap them easily without having to open the client classes, because these might be already in production, tested and a developer could potentially introduce new bugs and break things. One way to avoid this is to follow a principle called Open-Closed principle. Then you code to abstractions so you can easily inject concrete implementations via dependency injection.
Imagine the following escenario. For a bookstore, you have different implementations of how to save a book into a database e.g. using JDBC BookServiceJDBCImpl, or using an ORM BookServiceHibernateImpl etc..
// Create & get the Spring container, where you configure your implementations
// e.g. bookServiceJDBC, or bookServiceHibernate
ApplicationContext container = new ClassPathXmlApplicationContext("spring-config.xml");
// the container loads the appropriate bean say bookServiceHibernate
BookService bookService = (BookService) container.getBean("bookService");
//Create a new book this is a domain object usually you use new
Book newBook = new Book("1234", "Spring in Action","Rod Johnson");
//Now save the book using the implementation defined in the
//container
bookService.registerNewBook(newBook);
This is how part of the container file may look like, in here you define the concrete implementation:
<bean id="bookService" class="service.BookServiceHibernateImpl"/>
By letting the container handle this you could inject different implementations without having to touch the client class or even knowing which implementation will be passed.
Check this Dependency Injection blog post it explains a way to achieve it using Spring.
Bare in mind that in Spring you can use java annotations or xml, and that there are different ways to inject dependencies e.g. via get/set, constructors etc this is just an illustrative example of the general DI concept. The design is up to the developer.
Another reason why you would use beans is to aid testing.
We also extract the RestTemplate into a #Bean to make it easier to
test (it can be mocked more easily that way). Link
Why do people default to DI vs a global factory with a hashmap that maps interfaces/abstracts to classes? It would seem this is a higher performance solution to the problem no?
All the things mentioned so far in this thread can be provided by a global factory with a method like:
TestGlobalFactory implements GlobalFactoryI
ProductionGlobalFactory implements GlobalFactoryI //configures classes to interfaces
protected GlobalFactoryI gf=GlobalFactoryFactory.getInstance(); //only singleton used in app, specifies which GlobalFactory to use
protected SportsCarI mySportsCar=gf.new("sportsCarI",constructorVar1,constructorVar2);
The above would be much faster than recursive reflection to detect DI instances.
However I admittedly prefer the convention of DI as it ends up being fewer characters and greater flexibility with the option of third party containers.
artima.com/forums/flat.jsp?forum=106&thread=238700
Regardless DI, is the superior approach as it has the containers written to specify which implementation belongs in which class. With Service Locator one would actually have to do gf.new("thisClass","sportsCarI",constructor1)
The main advantage of dependency injection over a factory-based approach is not performance. Its main advantage is testability. The whole point of DI is to be able to inject mock dependencies to implement the unit tests of a component. Doing it with a factory is much more painful.
Because you get a lot more with Spring. Spring manages the lifecycle of its beans, in addition to caching instances in line with the user specified scope for the beans (e.g. prototype, singleton, etc). Also note that Spring's DI is related to its "Inversion of Control", so things are not hard coded directly into the app (unless you consider configuration code).
I find myself struggling with the fuzz around the concept of string-based 'Service Locators'.
For starters, IoC is great, and programming to interfaces is the way to go. But I fail to see where the big benefit lies in the yellow-pages pattern used here, apart from compilation-less reconfigurability .
Application code will use a (Spring) container to retrieve objects from. Now that's nice: since the code needs to know only the needed interface (to cast to), the Spring container interface, and the name of the needed object, a lot of coupling is removed.
public void foo(){
((MyInterface) locator.get("the/object/I/need")).callMe();
}
Where, of course, the locator can be populated with a gazillion of objects of all kind of Object derivatives.
But I'm a bit puzzled by the fact that the 'flexibility' of retrieving an object by name actually hides the dependency in a type-unsafe, lookup-unsafe manner: where my compiler used to check the presence of a requested object member, and it's type, now all of that is postponed to the runtime phase.
The simplest, functionally allright, pattern I could think of is a giant, application wide struct like object:
public class YellowPages {
public MyInterface the_object_i_need;
public YourInterface the_object_you_need;
....
}
// context population (no xml... is that bad?)
YellowPages locator = new YellowPages();
locator.the_object_i_need=new MyImpl("xyx",true),
locator.the_object_you_need=new YourImpl(1,2,3)
public void foo(){
locator.the_object_i_need.callMe(); // type-safe, lookup-safe
}
Would there be a way/pattern/framework to ask the compiler to resolve the requested object, and check whether it's type is ok? Are there DI frameworks that also do that?
Many thanks
What you are describing is an anti-pattern, plain and simple. Dependency injection (done via the constructor if possible) is the preferred way to do Inversion of Control. Older articles on IOC talk about service location as a viable way to implement the pattern, but you'd be hard pressed to find anyone advocating this in more recent writings.
You hit the nail on the head with this statement:
But I'm a bit puzzled by the fact that the 'flexibility' of retrieving
an object by name actually hides the dependency in a type-unsafe,
lookup-unsafe manner:
Most modern DI frameworks can get around the type-unsafe part, but they do hide the dependency by making it implicit instead of explicit.
Good article on this topic:
Service Locator is an Anti-Pattern
Spring is the only DI framework that I've used, so I can't speak for others, but even though Spring give you the ability to request an object by its name in your code, you don't have to get your Spring beans by name -- in fact, if you do, you're not really capitalizing on the "I" (inversion) in IOC.
The whole principle behind Spring/DI is that your objects shouldn't be asking for a particular object -- it should just have whatever objects it needs handed to it by the IOC container. The distinction is subtle, but it's there. The former approach would resemble the code that you pasted:
public void foo(){
((MyInterface) locator.get("the/object/I/need")).callMe();
}
The latter approach, by contrast, doesn't depend on any service locator, nor does it depend on the "name" of the object that it wants:
private ObjectINeed objectINeed;
public void setObjectINeed(ObjectINeed objectINeed) {
this.objectINeed = objectINeed;
}
public void foo(){
objectINeed.callMe();
}
It's the IOC container that calls the setObjectINeed() method. DI is definitely tackles the same problem as the service locator pattern, but it goes that extra step towards getting rid of the dependency on your service locator class.
We are using Spring for my application purposes, and Spring Testing framework for unit tests. We have a small problem though: the application code loads a Spring application context from a list of locations (XML files) in the classpath. But when we run our unit tests, we want some of the Spring beans to be mocks instead of full-fledged implementation classes. Moreover, for some unit tests we want some beans to become mocks, while for other unit tests we want other beans to become mocks, as we are testing different layers of the application.
All this means I want to redefine specific beans of the application context and refresh the context when desired. While doing this, I want to redefine only a small portion of the beans located in one (or several) original XML beans definition file. I cannot find an easy way to do it. It's always regarded that Spring is a unit-testing-friendly framework, so I must be missing something here.
Do you have any ideas how to do it?
Thanks!
I would propose a custom TestClass and some easy rules for the locations of the spring bean.xml:
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration(locations = {
"classpath*:spring/*.xml",
"classpath*:spring/persistence/*.xml",
"classpath*:spring/mock/*.xml"})
#Transactional
#TestExecutionListeners({
DependencyInjectionTestExecutionListener.class,
TransactionalTestExecutionListener.class,
DirtiesContextTestExecutionListener.class})
public abstract class AbstractHibernateTests implements ApplicationContextAware {
/**
* Logger for Subclasses.
*/
protected final Logger log = LoggerFactory.getLogger(getClass());
/**
* The {#link ApplicationContext} that was injected into this test instance
* via {#link #setApplicationContext(ApplicationContext)}.
*/
protected ApplicationContext applicationContext;
/**
* Set the {#link ApplicationContext} to be used by this test instance,
* provided via {#link ApplicationContextAware} semantics.
*/
#Override
public final void setApplicationContext(
final ApplicationContext applicationContext) {
this.applicationContext = applicationContext;
}
}
If there are mock-bean.xml in the specified location, they will override all "real" bean.xml files in the "normal" locations - your normal locations might differ.
But … I would never mix mock and non-mock beans, as it's hard to trace problems when the application grows older.
One of the reasons spring is described as test-friendly is because it may be easy to just new or mock stuff in the unit test.
Alternately we have used the following setup with great success, and I think it is quite close to what you want, I would strongly recommend it:
For all beans that need different implementations in different contexts, switch to annotation based wiring. You can leave the others as-is.
Implement the following set of annotations
<context:component-scan base-package="com.foobar">
<context:include-filter type="annotation" expression="com.foobar.annotations.StubRepository"/>
<context:include-filter type="annotation" expression="com.foobar.annotations.TestScopedComponent"/>
<context:exclude-filter type="annotation" expression="org.springframework.stereotype.Repository"/>
</context:component-scan>
Then you annotate your live implementations with #Repository, your stub implementations with #StubRepository, any code that should be present in the unit-test fixture ONLY with #TestScopedComponent. You may run into needing a couple more annotations, but these are a great start.
If you have a lot of spring.xml, you will probably need to make a few new spring xml files that basically only contain the component-scan definitions. You'd normally just append these files to your regular #ContextConfiguration list. The reason for this is because you frequently end up with different configurations of the context-scans (trust me, you will make at least 1 more annotations if you're doing web-tests, which makes for 4 relevant combinations)
Then you basically use the
#ContextConfiguration(locations = { "classpath:/path/to/root-config.xml" })
#RunWith(SpringJUnit4ClassRunner.class)
Note that this setup does not allow you to have alternating combinations of stub/live data. We tried this, and I think that resulted in a mess I wouldn't recommend anyone ;) We either wire inn the full set of stubs or the full set of live services.
We mainly use auto-wired stub dependencies when testing gui near stuff where the dependencies are usually quite substantial. In cleaner areas of the code we use more regular unit-testing.
In our system we have the following xml-files for component-scan:
for regular web production
for starting web with stubs only
for integration tests (in junit)
for unit tests (in junit)
for selenium web tests (in junit)
This means we totally have 5 different system-wide configurations that we can start the application with. Since we only use annotations, spring is fast enough to autowire even those unit tests we want wired. I know this is untraditional, but it's really great.
Out integration tests run with full live setup, and once or twice I have decided to get really pragmatic and want to have a 5 live wirings and a single mock:
public class HybridTest {
#Autowired
MyTestSubject myTestSubject;
#Test
public void testWith5LiveServicesAndOneMock(){
MyServiceLive service = myTestSubject.getMyService();
try {
MyService mock = EasyMock.create(...)
myTestSubject.setMyService( mock);
.. do funky test with lots of live but one mock object
} finally {
myTestSubject.setMyService( service);
}
}
}
I know the test purists are going to be all over me for this. But sometimes it's just a very pragmatic solution that turns out to be very elegant when the alternative would be really really ugly. Again it's usually in those gui-near areas.
See this tutorial with #InjectedMock annotation
It saved me a lot of time. You just use
#Mock
SomeClass mockedSomeClass
#InjectMock
ClassUsingSomeClass service
#Before
public void setUp() {
MockitoAnnotations.initMocks(this);
}
and all your problems are solved. Mockito will replace the spring dependency injection with a mock. I just used it myself and it works great.
There are some very complicated and powerful solutions listed here.
But there is a FAR, FAR simpler way to accomplish what Stas has asked, which doesn't involve modifying anything other than one line of code in the test method. It works for unit tests and Spring integration tests alike, for autowired dependencies, private and protected fields.
Here it is:
junitx.util.PrivateAccessor.setField(testSubject, "fieldName", mockObject);
You can also write your unit tests to not require any lookups at all:
#ContextConfiguration(locations = { "classpath:/path/to/test-config.xml" })
#RunWith(SpringJUnit4ClassRunner.class)
public class MyBeanTest {
#Autowired
private MyBean myBean; // the component under test
#Test
public void testMyBean() {
...
}
}
This gives an easy way to mix and match real config files with test config files.
For example, when using hibernate, I might have my sessionFactory bean in one config file (to be used in both the tests and the main app), and have by dataSource bean in another config file (one might use a DriverManagerDataSource to an in-memory db, the other might use a JNDI-lookup).
But, definitely take heed of #cletus's warning ;-)
Easy. You use a custom application context for your unit tests, or you don't use one at all and you manually create and inject your beans.
It sounds to me like your testing might be a bit too broad. Unit testing is about testing, well, units. A Spring bean is a pretty good example of a unit. You shouldn't need an entire application context for that. I find that if your unit testing is so high-level that you need hundreds of beans, database connections etc., you have a really fragile unit test that is going to break on the very next change, will be hard to maintain and really isn't adding a lot of value.
You can use the import feature in your test app context to load in the prod beans and override the ones you want. For example, my prod data source is usually acquired via JNDI lookup, but when I test I use a DriverManager data source so I don't have to start the app server to test.
I don't have the reputation points to pile on duffymo's answer, but I just wanted to chime in and say his was the "right" answer for me.
Instantiate a FileSystemXmlApplicationContext in your unit test's setup with a custom applicationContext.xml. In that custom xml, at the top, do an as duffymo indicates. Then declare your mock beans, non-JNDI data sources, etc, that will override the id's declared in the import.
Worked like a dream for me.
You do not need to use any test contexts (doesn't matter is XML or Java based). Since Spring boot 1.4 there is available new annotation #MockBean which introduced native support for mocking and Spying of Spring Beans.
Perhaps you could use qualifiers for your beans? You would redefine the beans you want to mock up in a separate application context and label them with a qualifier "test". In your unit tests, when wiring your beans always specify the qualifier "test" to use the mock ups.
I want to do the same thing, and we're finding it essential.
The current mechanism we use is fairly manual but it works.
Say for instance, you wish to mock out bean of type Y. What we do is every bean that has that dependency we make implement an interface - "IHasY". This interface is
interface IHasY {
public void setY(Y y);
}
Then in our test we call the util method...
public static void insertMock(Y y) {
Map invokers = BeanFactory.getInstance().getFactory("core").getBeansOfType(IHasY.class);
for (Iterator iterator = invokers.values().iterator(); iterator.hasNext();) {
IHasY invoker = (IHasY) iterator.next();
invoker.setY(y);
}
}
I do not want to create a whole xml file just to inject this new dependency and that is why I like this.
If you're willing to create an xml config file then the way to go would be to create a new factory with the mock beans and make your default factory a parent of this factory. Make sure then that you load all your beans from the new child factory. When doing this the sub-factory will override the beans in the parent factory when the bean id's are the same.
Now if, in my test, If I could programmatically create a factory, that would be awesome. Having to use xml is just too cumbersome. I'm looking to create that child factory with code. Then each test can configure its factory the way it wants. There's no reason why a factory like that won't work.
spring-reinject is designed to substitute beans with mocks.
Since the OP this has come along: Springockito