java - Spring Boot @SpringBootApplication类上找不到默认构造函数

我想知道为什么字段注入(inject)在@SpringBootApplication类中起作用而构造函数注入(inject)却不起作用。

我的ApplicationTypeBean可以正常工作，但是当我想要CustomTypeService的构造函数注入(inject)时，我收到此异常:

Failed to instantiate [at.eurotours.ThirdPartyGlobalAndCustomTypesApplication$$EnhancerBySpringCGLIB$$2a56ce70]: No default constructor found; nested exception is java.lang.NoSuchMethodException: at.eurotours.ThirdPartyGlobalAndCustomTypesApplication$$EnhancerBySpringCGLIB$$2a56ce70.<init>()

是否有任何原因使它在@SpringBootApplication类上不起作用？

我的SpringBootApplication类:

@SpringBootApplication
public class ThirdPartyGlobalAndCustomTypesApplication implements CommandLineRunner{

@Autowired
ApplicationTypeBean applicationTypeBean;

private final CustomTypeService customTypeService;

@Autowired
public ThirdPartyGlobalAndCustomTypesApplication(CustomTypeService customTypeService) {
    this.customTypeService = customTypeService;
}

@Override
public void run(String... args) throws Exception {
    System.out.println(applicationTypeBean.getType());
    customTypeService.process();
}

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

public CustomTypeService getCustomTypeService() {
    return customTypeService;
}

我的@Service类:

@Service
public class CustomTypeService {

    public void process(){
        System.out.println("CustomType");
    }
}

我的@Component类:

@Component
@ConfigurationProperties("application.type")
public class ApplicationTypeBean {

    private String type;

最佳答案

SpringBootApplication是一个元注释，其中:

// Other annotations
@Configuration
@EnableAutoConfiguration
@ComponentScan
public @interface SpringBootApplication { ... }

因此，以百分数计，您的ThirdPartyGlobalAndCustomTypesApplication也是Spring Configuration类。如Configuration的javadoc所述:



因此，您不能对Configuration类使用构造函数注入(inject)。显然，它将基于this answer和此jira ticket在4.3版本中进行修复。