How to test constructor of a class that has a @PostConstruct method using Spring?

Question

If I have a class with a @PostConstruct method, how can I test its constructor and thus its @PostConstruct method using JUnit and Spring? I can't simply use new ClassName(param, param) because then it's not using Spring -- the @PostConstruct method is not getting fired.

Am I missing something obvious here?

public class Connection {
    private String x1;
    private String x2;

    public Connection(String x1, String x2) {
        this.x1 = x1;
        this.x2 = x2;
    }

    @PostConstruct
    public void init() {
        x1 = "arf arf arf";
    }

}


@Test
public void test() {
    Connection c = new Connection("dog", "ruff");
    assertEquals("arf arf arf", c.getX1());
}

I have something similar (though slightly more complex) than this and the @PostConstruct method does not get hit.

Cryptomeria

Answer 1

Have a look at Spring JUnit Runner.

You need to inject your class in your test class so that spring will construct your class and will also call post construct method. Refer the pet clinic example.

eg:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:your-test-context-xml.xml")
public class SpringJunitTests {

    @Autowired
    private Connection c;

    @Test
    public void tests() {
        assertEquals("arf arf arf", c.getX1();
    }

    // ...

Despair

I understand that, as I stated. But how do I test multiple permutations of this constructor inside one test class? What am I not making clear about my question? – Cryptomeria

I want five test cases for this class's constructor. Is there really no better way than to have an app context with five such beans and load it up? – Cryptomeria

In real time if there are 5 possible ways to inject your class then am afraid to say that you have to create 5 bean definitions in that case. – Despair

I'll just test the @PostConstruct method by calling it on the object. – Cryptomeria

Answer 2

If the only container managed part of Connection is your @PostContruct method, just call it manually in a test method:

@Test
public void test() {
  Connection c = new Connection("dog", "ruff");
  c.init();
  assertEquals("arf arf arf", c.getX1());
}

If there is more than that, like dependencies and so on you can still either inject them manually or - as Sridhar stated - use spring test framework.

Calliper

That's what I ended up doing. – Cryptomeria

the init can be private – Levy

@shanyangqu Then you could use ReflectionTestUtils or equivalent for instance. It's test code afterall. – Calliper

@Calliper I know, just thinking its worth mentioning... also I find deencapsulate is more powerful.... thean ReflectionTestUtils – Levy

@Cryptomeria this should be added to the accepted answer. I did not want to burden my test with the entire SpringJUnit4Runner class and simply calling the method seemed to work just fine. This answer works in cases where the tester wants to test the target class without worrying about the spring context. – Profundity

Does ReflectionTestUtils or a similar tool have a way to explicitly call @PostConstruct methods? Or do you always do it by method name? Only looking for the way that will be least prone to refactoring issues :) – Bourgeon

@Bourgeon I haven't seen any library that does that directly but it's possible using reflection api - iterate over class methods, find one annotated with @PostConstruct and call it for your object. – Calliper

Answer 3

@PostConstruct must be changing the state of the object. So, in JUnit test case, after getting the bean check the state of the object. If it is same as the state set by @PostConstruct, then the test is success.

Backsaw

The problem isn't how to test that it's changed, but that @PostConstruct is not getting fired. I'll edit my post to make that more clear. – Cryptomeria

Answer 4

By default, Spring will not aware of the @PostConstruct and @PreDestroy annotation. To enable it, you have to either register ‘CommonAnnotationBeanPostProcessor‘ or specify the ‘‘ in bean configuration file.

<bean class="org.springframework.context.annotation.CommonAnnotationBeanPostProcessor" />

or

<context:annotation-config />

Backsaw