Spring JUnit4 manual-/auto-wiring dilemma

Question

I ran into an issue that can only be explained with my fundamental lack of understanding of Spring's IoC container facilities and context setup, so I would ask for clarification regarding this.

Just for reference, an application I am maintaing has the following stack of technologies:

• Java 1.6
• Spring 2.5.6
• RichFaces 3.3.1-GA UI
• Spring framework is used for bean management with Spring JDBC module used for DAO support
• Maven is used as build manager
• JUnit 4.4 is now introduced as test engine

I am retroactively (sic!) writing JUnit tests for the application and what suprised me is that I wasn't able to inject a bean into a test class by using setter injection without resorting to @Autowire notation.

Let me provide set up an example and accompanying configuration files.

The test class TypeTest is really simple:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class TypeTest {

    @Autowired
    private IType type;

    @Test
    public void testFindAllTypes() {
        List<Type> result;

        try {
            result = type.findAlltTypes();
            assertNotNull(result);
        } catch (Exception e) {
            e.printStackTrace();
            fail("Exception caught with " + e.getMessage());
        }
    }
}

Its context is defined in TestStackOverflowExample-context.xml:

<context:property-placeholder location="classpath:testContext.properties" />
<context:annotation-config />
<tx:annotation-driven />

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
    destroy-method="close">
    <property name="driverClassName" value="${db.connection.driver.class}" />
    <property name="url" value="${db.connection.url}" />
    <property name="username" value="${db.connection.username}" />
    <property name="password" value="${db.connection.password}" />
</bean>

<bean id="transactionManager"
    class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource" />
</bean>

<bean id="beanDAO" class="com.example.BeanDAOImpl">
    <property name="ds" ref="dataSource"></property>
    <property name="beanDAOTwo" ref="beanDAOTwo"></property>
</bean>

<bean id="beanDAOTwo" class="com.example.BeanDAOTwoImpl">
    <property name="ds" ref="dataSource"></property>
</bean>

<bean id="type" class="com.example.TypeImpl">
    <property name="beanDAO" ref="beanDAO"></property>
</bean>

TestContext.properties is in classpath and contains only db-specific data needed for datasource.

This works like a charm but my question is - why doesn't it work when I try to manually wire beans and perform setter injection as in:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class TypeTest {

    private IType type;

    public IType getType () {
        return type;
    }

    public void setType(IType type) {
        this.type= type;
    }

    @Test
    public void testFindAllTypes(){
    //snip, snip...
    }
}

What am I missing here? What part of configuration is wrong here? When I try to manually inject beans via setters, test fails because this part

result = type.findAlltTypes();

is resolved as null in runtime. I've, of course, consulted the Spring reference manual and tried various combinations of XML configuration; all I could conclude is that Spring was unable to inject beans because it somehow fails to properly dereference Spring Test Context reference but by using @Autowired this happens "automagically" and I really can't see why is that because JavaDoc of both Autowired annotation and its PostProcessor class doesn't mention this.

Also worth adding is the fact that @Autowired is used in application only here. Elsewhere only manual wiring is performed, so this also brings forth question - why is it working there and not here, in my test? What part of DI configuration am I missing? How does @Autowired get reference of Spring Context?

EDIT: I've also tried this but with same results:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class TypeTest implements ApplicationContextAware{

    private IType type;

    private ApplicationContext ctx;

    public TypeTest(){
              super();
              ctx = new FileSystemXmlApplicationContext("/TypeTest-context.xml");
              ctx.getBean("type");
    }

    public IType getType () {
        return type;
    }

    public void setType(IType type) {
        this.type= type;
    }

    @Test
    public void testFindAllTypes(){
    //snip, snip...
    }
}

Any other ideas, perhaps?

EDIT2: I've found a way without resorting to writing own TestContextListener or BeanPostProcessor. It is suprisingly simple and it turns out that I was on the right track with my last edit:

1) Constructor-based context resolving:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class TypeTest{

    private IType type;

    private ApplicationContext ctx;

    public TypeTest(){
         super();
         ctx = new FileSystemXmlApplicationContext("/TypeTest-context.xml");
         type = ctx.getBean("type");
    }

    public IType getType () {
        return type;
    }

    public void setType(IType type) {
        this.type= type;
    }

    @Test
    public void testFindAllTypes(){
    //snip, snip...
    }
}

2) By implementing ApplicationContextAware interface:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class TypeTest implements ApplicationContextAware{

    private IType type;
    private ApplicationContext ctx;

    public IType getType () {
        return type;
    }

    public void setType(IType type) {
        this.type= type;
    }

@Override
    public void setApplicationContext(ApplicationContext ctx) throws BeansException {
    this.ctx = ctx;
    type = (Type) ctx.getBean("type");
}

    @Test
    public void testFindAllTypes(){
    //snip, snip...
    }
}

Both of these approaches properly instanced beans.

Answer 1

If you take a look at the source of org.springframework.test.context.support.DependencyInjectionTestExecutionListener, you will see the following method (formatted and commented for clarity):

protected void injectDependencies(final TestContext testContext)
throws Exception {
    Object bean = testContext.getTestInstance();
    AutowireCapableBeanFactory beanFactory = testContext.getApplicationContext()
            .getAutowireCapableBeanFactory();
    beanFactory.autowireBeanProperties(bean, 

            AutowireCapableBeanFactory.AUTOWIRE_NO,
            // no autowiring!!!!!!!!

            false
        );

    beanFactory.initializeBean(bean, testContext.getTestClass().getName());
    // but here, bean post processors are run

    testContext.removeAttribute(REINJECT_DEPENDENCIES_ATTRIBUTE);
}

So the test object is a bean without auto-wiring. However, @AutoWired, @Resource etc, don't use the autowiring mechanism, they use BeanPostProcessor. And so the dependencies are injected if and only if the annotations are used (or if you register some other BeanPostProcessor that does it).

(The above code is from Spring 3.0.x, but I bet it was the same in 2.5.x)