@RunWith(SpringJUnit4ClassRunner.class) Can not load an ApplicationContext with a NULL 'contextLoader'

Question

I hava this code ,

@RunWith(SpringJUnit4ClassRunner.class)
public class JunitDemo {

    @Test
    public void testAssertArrayEquals() {

        byte[] expected = "trial".getBytes();
        byte[] actual = "trial".getBytes();

        Assert.assertArrayEquals("fail", expected, actual);
    }
}

and run the test, there are errors

Caused by: java.lang.IllegalArgumentException: Can not load an ApplicationContext with a NULL 'contextLoader'. Consider annotating your test class with @ContextConfiguration. at org.springframework.util.Assert.notNull(Assert.java:112) at org.springframework.test.context.TestContext.loadApplicationContext(TestContext.java:276) at org.springframework.test.context.TestContext.getApplicationContext(TestContext.java:304) ... 28 more

then, i find a same Q with SO,the solution is

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

    @Resource
    private ApplicationContext ApplicationContext;

    @Test
    public void testAssertArrayEquals() {

        byte[] expected = "trial".getBytes();
        byte[] actual = "trial".getBytes();

        Assert.assertArrayEquals("fail", expected, actual);
    }
}

in fact，for this pojo, i do'nt need the xml config. and i will get other error

Caused by: java.io.FileNotFoundException: class path resource [/JunitDemo-context.xml] cannot be opened because it does not exist at org.springframework.core.io.ClassPathResource.getInputStream(ClassPathResource.java:158) at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:328) ... 37 more

How to correctly run my program ？

Answer 1

From the @ContextConfiguration docs:

@ContextConfiguration defines class-level metadata that is used to determine how to load and configure an ApplicationContext for integration tests.

Annotation itself has property loader and doc says:

If not specified, the loader will be inherited from the first superclass that is annotated with @ContextConfiguration and specifies an explicit loader. If no class in the hierarchy specifies an explicit loader, a default loader will be used instead.

The default concrete implementation chosen at runtime.

So you can specify context loader directly with loader property. To navigate to direct configuration use locations for xml and classes for annotated class config.

In you case looks like spring chosen GenericXmlContextLoader for context loading, you don't specify location so ApplicationConext will be loaded from "classpath:/com/example/<your _test_class_name>-context.xml"

This is good article about it.