When @Autowired is used, dependencies need to be resolved when the class is instantiated, which may cause early initialization of
beans or lead the context to look in places it shouldn’t to find the bean. To avoid this tricky issue and optimize the way the context loads,
dependencies should be requested as late as possible. That means using parameter injection instead of field injection for dependencies that are only
used in a single @Bean method.
Noncompliant code example
@Configuration
public class FooConfiguration {
@Autowired private DataSource dataSource; // Noncompliant
@Bean
public MyService myService() {
return new MyService(this.dataSource);
}
}
Compliant solution
@Configuration
public class FooConfiguration {
@Bean
public MyService myService(DataSource dataSource) {
return new MyService(dataSource);
}
}
Exceptions
Fields used in methods that are called directly by other methods in the application (as opposed to being invoked automatically by the Spring
framework) are ignored by this rule so that direct callers don’t have to provide the dependencies themselves.
