配置类中的Spring MVC Default或no-arg构造函数

Question

@Configuration
public class ApplicationConfig {

   private DataSource dataSource;

  @Autowired
  public ApplicationConfig(DataSource dataSource) {
    this.dataSource = dataSource;
  }

  @Bean(name="clientRepository")
  ClientRepository jpaClientRepository() {
    return new JpaClientRepository();
   }
}

I just found a Core Spring 4.2 Certification Mock Exam and regarding this class it says that "Default or no-arg constructor is mandatory."
I tried this class in a test I made and it works perfectly without Default or no-arg constructor (?) , SO I think there is no need of a Default or no-arg constructor

Answer 1

If your Spring version is <= 4.2 then that statement is true. However for Spring >= 4.3 it is allowed to have a @Configuration class without a no-args constructor.

See also the Core Container Improvements section in the reference guide about this. It has been implemented with issue SPR-13471 in Spring 4.3 RC1.

Pro Tip: if you only have a single constructor you don't need @Autowired on the constructor anymore. (See SPR-12278 ) for that).