SpringBoot REST API应用程序中的依赖注入

Question

I'm a newbie in Spring, and I am trying to understand and leverage Dependency Injection to achieve this solution.

I have interface B and class ServiceB. ServiceB depends on B. I have configured it as such in the application Class

@SpringBootApplication
public class Application {

public static void main(String[] args) {
    SpringApplication.run(ServiceNowMediatorApplication.class, args);
}
@Bean
public B b(){
    return new BImpl();
}


@Bean
public ServiceB serviceB(B b){
    return new ServiceB(b);
}

}

BImpl class implements Interface B

The b object is received as the body of a POST call

@RestController
@RequestMapping("/{database}/alerts")
public class ControllerB {
  @Autowired private ServiceB serviceB;

  @Autowired
  private B b;

  @Autowired
  ControllerB(B b,ServiceB serviceB){
      this.b = b;
      this.serviceB = serviceB;
  }

  @RequestMapping(method = RequestMethod.POST)
  public B dosomethingCrazy(@RequestBody BImpl bimpl)  {


      String response = serviceB.dosomethingImportant();
      return bimpl;

  }

}

The thing is that the 'dosomethingimportant' function in serviceB refers the autowired bean of B. The problem is that it does not seem to have any of B's attributes which have been passed in the POST call.

@Service
public class ServiceB {


@Autowired
public B b;

@Autowired
public B getB() {
    return b;
}

@Autowired
public void setB(B b) {
    this.b = b;
}

@Autowired
public ServiceB(B b){
    this.b = b;

}

public String dosomethingimportant() {
  b.getValueOfFieldPassedInPOST(field1) ==> THIS RETURNS A NULL
 }

I don't understand why B is not being autowired in correctly.

For example, if I POST {hello:world} , then b.getHello() in ServiceB class should return me back 'world'

However if I change the dosomethingCrazy() function in the Controller class add a setB(B b) before calling dosomethingimportant() function, then everything works great. As below

  @RequestMapping(method = RequestMethod.POST)
  public B dosomethingCrazy(@RequestBody BImpl bimpl)  {

      **serviceB.setB(bimpl);**
      String response = serviceB.dosomethingImportant();
      return bimpl;

  }

How can I proceed with this without having to do a setB() function? Am I not understanding DI correctly here? What would be the best way to design this solution?

Thanks so much!

Answer 1

This might not be a complete solution but it resolves some mistakes!

@SpringBootApplication
public class Application {

  public static void main(String[] args) {
    SpringApplication.run(ServiceNowMediatorApplication.class, args);
  }
  @Bean
  public B b(){
    /*return new B();*/ // B is an interface according to you
    // e.g. you have BImpl, so probably return new BImpl();
    return /*<class that implements B>*/;
  }

  @Bean
  public ServiceB serviceB(B b){
    return new ServiceB(b);
  }

}

The controller :

@RestController
@RequestMapping("/{database}/alerts")
public class ControllerB {
  @Autowired 
  private ServiceB serviceB;

  @Autowired
  private B b;

  // not need this
  /*@Autowired
  ControllerB(B b,ServiceB serviceB){
      this.b = b;
      this.serviceB = serviceB;
  }*/

  @RequestMapping(method = RequestMethod.POST)
  public B dosomethingCrazy(@RequestBody BImpl bimpl)  {
      // this doesn't make much sense!
      // BImpl looks like implementation of B (e.g. is some component or service)
      // You better create some model object that represents data you're getting on POST 
      // and change method arg to smth. like that @RequestBody SomeModel model
      String response = serviceB.dosomethingImportant();

      // it is a controller's method that handles POST, it should return
      // something else - either data or some OK status
      return bimpl;

  }

}

The service :

@Service
public class ServiceB {

  @Autowired
  public B b;

  /*@Autowired // already, check the prev line
  public B getB() {
    return b;
  }*/

  /*@Autowired
  public void setB(B b) {
    this.b = b;
  }*/

  /*@Autowired
  public ServiceB(B b){
    this.b = b;
  }*/

  public String dosomethingimportant() {
    // what is field1 ? maybe it makes sense to add it as param
    // like public String dosomethingimportant(String f1) or so
    b.getValueOfFieldPassedInPOST(field1) ==> THIS RETURNS A NULL
  }
}

I haven't remove anything, just commented out some stuff and left some comments. Maybe this may help to get a more clear picture of where you should start.