Why Getting Spring Beans in Non‑Spring Classes Causes NullPointerExceptions

In non‑Spring‑managed classes, retrieving Spring beans can cause issues such as NullPointerExceptions and failed autowiring.

Case 1

Utility class SpringContextUtils provides a way to obtain beans from the application context.

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class SpringContextUtils implements ApplicationContextAware {
    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        SpringContextUtils.applicationContext = applicationContext;
    }

    public static <T> T getBean(Class<T> clazz) {
        // Ensure the Spring container is initialized before using this utility,
        // otherwise a NullPointerException may be thrown.
        return applicationContext.getBean(clazz);
    }
}

Plain class using the utility:

public class PlainClass {
    public void foo1() {
        TheOtherBean bean = SpringContextUtils.getBean(TheOtherBean.class);
        System.out.println(bean);
    }
}

Calling foo1 from a Spring bean works, but calling it from a non‑Spring class throws a NullPointerException because SpringContextUtils is not managed and its applicationContext is null.

Case 2

Plain class with an @Autowired field:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

public class PlainClass {
    @Autowired
    private TheOtherBean theOtherBean;

    public void foo2() {
        System.out.println(theOtherBean);
    }
}

@Component
public class TheOtherBean { }

When foo2 is invoked from a Spring bean, the output is null because PlainClass is not a Spring component, so the autowired field is not injected.

The IDE warns: “Autowired members must be defined in valid Spring bean (@Component|@Service|…)”.

Executing the same call from a non‑Spring class also yields null.

Test class

package jstudy.beantest;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@SpringBootTest
@RunWith(SpringRunner.class)
public class BeanTest {
    @Test
    public void test() {
        new PlainClass().foo2();
    }
}

Removing @SpringBootTest and @RunWith turns BeanTest into a plain Java class, i.e., a non‑Spring bean.

Summary

Directly obtaining Spring beans in non‑Spring classes can lead to NullPointerExceptions and failed autowiring. The recommended practice is to register any class that needs to access Spring beans as a Spring component so that dependencies are managed correctly.