How can I get a Spring bean in a servlet filter?

I have defined a javax.servlet.Filter and I have Java class with Spring annotations.

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Bean;

@Configuration
public class SocialConfig {

    // ...

    @Bean
    public UsersConnectionRepository usersConnectionRepository() {
        // ...
    }
}

I want to get the bean UsersConnectionRepository in my Filter, so I tried the following:

public void init(FilterConfig filterConfig) throws ServletException {
    UsersConnectionRepository bean = (UsersConnectionRepository) filterConfig.getServletContext().getAttribute("#{connectionFactoryLocator}");
}

But it always returns null. How can I get a Spring bean in a Filter?

There are three ways:

1. Use WebApplicationContextUtils:

   public void init(FilterConfig cfg) { 
       ApplicationContext ctx = WebApplicationContextUtils
         .getRequiredWebApplicationContext(cfg.getServletContext());
       this.bean = ctx.getBean(YourBeanType.class);
   }
   

2. Using the DelegatingFilterProxy - you map that filter, and declare your filter as bean. The delegating proxy will then invoke all beans that implement the Filter interface.

3. Use @Configurable on your filter. I would prefer one of the other two options though. (This option uses aspectj weaving)

Try:

UsersConnectionRepository bean = 
  (UsersConnectionRepository)WebApplicationContextUtils.
    getRequiredWebApplicationContext(filterConfig.getServletContext()).
    getBean("usersConnectionRepository");

Where usersConnectionRepository is a name/id of your bean in the application context. Or even better:

UsersConnectionRepository bean = WebApplicationContextUtils.
  getRequiredWebApplicationContext(filterConfig.getServletContext()).
  getBean(UsersConnectionRepository.class);

Also have a look at GenericFilterBean and its subclasses.