@Postconstruct annotations and initializingbean perform some initialization operations after bean instantiation

At first it was this code ：

@Service
public class userService {
    

    @Autowired
    private BaseConfig baseConfig;


    private IClient client;

	public userService () {
    
		client = ClientFactory.getClient(IClient.class, baseConfig.getBaseUrl());
    }

	public userinfo getUserInfo(){
    
		return client.getUserInfos();
	}

}

As a result, when the program starts running , Found calling in constructor baseConfig The result is baseConfig by null.

Later, we found that ,java stay bean During initialization , Is to execute the constructor of the class first , Instantiate an ordinary object , Then put this ordinary The instance object is stored in singletonFactories Of map in , Subsequent passing inspection Whether circular dependency and APO After operation , Execute initialization of the instance object , Let me put the initialized instance object into the singleton pool .

So in the above operation , By construction method , Get the instance field of dependency injection , It's unrealistic .

resolvent ：
One 、 Through annotation @PostConstruct Realize in bean Initialization after instantiation .

@Service
public class userService {
    

    @Autowired
    private BaseConfig baseConfig;


    private IClient client;
	
	@PostConstruct
	public void initClient () {
    
		client = ClientFactory.getClient(IClient.class, baseConfig.getBaseUrl());
    }

	public userinfo getUserInfo(){
    
		return client.getUserInfos();
	}

}

Two 、 By implementing InitializingBean Interface , Realize in bean Initialization after instantiation .

@Service
public class userService  implements InitializingBean {
    

    @Autowired
    private BaseConfig baseConfig;


    private IClient client;
	
    @Override
    public void afterPropertiesSet() throws Exception {
    
		client = ClientFactory.getClient(IClient.class, baseConfig.getBaseUrl());
    }

	public userinfo getUserInfo(){
    
		return client.getUserInfos();
	}
}