Spring Boot @Autowired creating instances on a runtime

问题

As most of Spring Boot new users I have a problem with @Autowired :D

I've readed a big amount of topics about this annotation here But still can't find proper solution for my problem.

Let's suppose that we have this Spring Boot hierarchy:

@SpringBootApplication
public class DemoApplication {

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

Class, that we wanna instantiate every time it's called:

@Service
public class TestWire {
    public TestWire() {
        System.out.println("INSTANCE CREATED: " + this);
    }
}

Out get controller, that creates new SomeRepo object every request:

@RestController
public class CreatingRepo {
    @RequestMapping("/")
    public void postMessage() {
        SomeRepo repo = new SomeRepo();
    }
}

Finally, class, that uses @Autowired to create TestWire instances:

public class SomeRepo {
    @Autowired
    private TestWire testWire;

    public SomeRepo() {
        System.out.println(testWire.toString());
    }
}

Let's assume, that we make GET request to "/" several times.

So, as a result, TestWire class will isntantiate only when project builds and neither @Scope(value = "prototype"), nor proxyMode = ScopedProxyMode.TARGET_CLASS wont help.

Any ideas how to create new instances at runtime? I mean, how can we do it in "Spring way"? Without factories and other things, only Spring DI through annotation and configuration.

Upd. A piece of stack trace, where instance created:

2015-11-16 20:30:41.032  INFO 17696 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
INSTANCE CREATED: com.example.TestWire@56c698e3
2015-11-16 20:30:41.491  INFO 17696 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@12f41634: startup date [Mon Nov 16 20:30:37 MSK 2015]; root of context hierarchy
2015-11-16 20:30:41.566  INFO 17696 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/]}" onto public void com.example.CreatingRepo.postMessage()

回答1:

If I understood you correct you need to annotate the SomeRepo like this:

@Service
@Scope(value = "prototype")
public class SomeRepo { 
// ...
}

Option A:

Instead of instantiating the class with new SomeRepo(); you ask the BeanFactory.getBean(...) for it.

@RestController
public class CreatingRepo {
    @Autowired
    BeanFactory beanFactory;

    @RequestMapping("/")
    public void postMessage() {
        // instead of new SomeBean we get it from the BeanFactory
        SomeRepo repo = beanFactory.getBean(SomeRepo.class);
    }
}

Option B:

You should also be able to get the Bean like this (over paramters without the beanFactory):

@RestController
public class CreatingRepo {

    @RequestMapping("/")
    public void postMessage(SomeRepo repo) {
        // instead of the BeanFactory and using new SomeRepo you can get it like this.
    }
}

来源：https://stackoverflow.com/questions/33740510/spring-boot-autowired-creating-instances-on-a-runtime

标签

java

Spring

dependency-injection

spring-boot

autowired