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Asked: 2020-03-23 04:31:30 +0800 CST 2020-03-23 04:31:30 +0800 CST

Null dependencies with singleton pattern

  • 772

I have a class that I call from another class:

public class caller {
    @Test
    public void test() throws Exception {
        Calle.getInstance().run();
    }
}

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@RunWith(SpringRunner.class)
@SpringBootTest(classes = { Swagger2SpringBoot.class }, webEnvironment = WebEnvironment.DEFINED_PORT)
@ActiveProfiles("api")
public final class Calle extends AbstractTest {

    @Autowired
    private UserApi userApi;

    private static final Calle INSTANCE = new Calle();

    public static Calle getInstance() {
        return Calle.INSTANCE;
    }

    private Calle() {
    }

    public void run() throws Exception {
        final User usr1 = this.createUser(this.userApi);
    }
}

 MAIN

@ComponentScan(
    basePackages = {
         "es.comp.api",
         "es.comp.api.controller",
         "es.comp.api.configuration"
    }

The UserApi class is added in the main ("es.comp.api.controller",)

Apparently and from what I could read. When a class is called in a singleton. Spring does not load dependencies that are loaded with the @Autowired tag. So when doing the this.createUser(this.userApi) it gives me a NullPointerException.

How could I solve this error? All the best

spring-boot

1 Answers

  1. Best Answer

    When you use Spring to instantiate any object, Spring takes care of parsing its class and finding dependencies. If you create an instance of any class by manually calling its constructor, that instance is not known to Spring and therefore it won't inject anything into it. The easiest solution would be to keep using Spring to get the instance, something like:

    @Bean
public class caller {

    @Autowired private Calle c;

    @Test
    public void test() throws Exception {
        this.c.run();
    }
}
    • 1