How do I autowire an instance of a java class?

Question

I have a class that starts like this:

import javax.mail.Session;
//... more imports

@Component("eMailUtility")
public class MailUtility {

  @Autowired
  Session mailSession;
  //...
}

My IDE tells me "Could not autowire. No beans of 'Session' type found."

This message doesn't surprise me, but I'm not sure how to fix it. Session is a final class with factory methods but no public constructors. I can easily instantiate a Session somewhere, but I don't know what I need to do to make it recognizable as a target of an autowired injection. All the examples I've found on the internet show how to autowire an instance of a class that I wrote, which doesn't help me here.

(A detailed explanation of exactly how autowire works, which doesn't gloss over anything, would be very helpful, but I can't seem to find one. If you know of a good link, that would be helpful.)

score 1 · Answer 1 · answered May 05 '17 at 23:42

You'd have to create a method in a class that is annotated with @Configuration that returns a Session object and annotate that method with @Bean. In your case something like this:

@Bean
public Session session() {
    return <instance>;
}

If it was one of your own classes you could also annotate it with @Component, or other annotations that are itself annotated with @Component. Spring would then find the class with this annotation and automatically create the bean for you.

For an explanation about @Autowired you can look at this answer: Understanding Spring @Autowired usage

You should also have a @ComponentScan annotation in your application (your main class, if possible) with a base_packages attribute that specifies the package of this class. — MiguelMunoz, May 23 '22 at 23:49

How do I autowire an instance of a java class?

1 Answers1