Spring Boot Data MongoDB - Repository is null

Question

I want to develop a little test application using Spring Boot and Spring Data MongoDB. So, in this case, I use default configuration (like localhost:27017/test database) and I try to follow the spring guide ( https://spring.io/guides/gs/accessing-data-mongodb/ ).

I launch my application like this:

@SpringBootApplication
public class Application implements CommandLineRunner {
    private static final Logger LOGGER = LoggerFactory.getLogger(Application.class);

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Override
    public void run(String... strings) throws Exception {
        (new DummyClass()).load();
    }
}

The DummyClass is as following:

@org.springframework.stereotype.Component
@ConfigurationProperties(prefix="dummy")
public class DummyClass {

    private static String url;
    private List<Project> projects;


    @Autowired
    private ProjectRepository projectRepository;


    public void setUrl(String url) {
        DummyClass.url = url;
    }


    @Override
    public void load() {

       // (...) creating some project objects

       projectRepository.deleteAll();
       projectRepository.save(this.projects);
    }    
}

When the projectRepository.deleteAll() statement is executed, I receive un NullPointerException.

For information, below the ProjectRepository interface:

public interface ProjectRepository extends MongoRepository<Project, String>     
{ 
}

And my package structure is: com.test.dummy Application.java com.test.dummy.components DummyClass.java com.test.dummy.domain Project.java com.test.dummy.repositories ProjectRepository.java

Can you help me to understand my error?

Note: I use Spring Boot 1.4.1 and Mongo 3.2

Answer 1

Inside your Application.run() method you instantiate your DummyClass outside of the Spring context ( new DummyClass() ). This way the

@Autowired
private ProjectRepository projectRepository;

is not instantiated correctly.

You should inject your DummyClass via Spring and not create a new instance of it via its constructor.

Example:

@SpringBootApplication
public class Application implements CommandLineRunner {
    private static final Logger LOGGER = LoggerFactory.getLogger(Application.class);

    @Autowired
    DummyClass dummyClass;

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Override
    public void run(String... strings) throws Exception {
       dummyClass.load();
    }
}