Spring - Using Beans in HTTP Servlet

So you want to use your beautiful and shining Spring Beans in ugly and ordinary HTTP Servlet? Don't be ashamed ;) Sometimes we all have to do it, and we do it in many different ways ;) Below you may find few examples.

Old-fashioned way :) - used by me till some beautiful Thursday morning ...

public class BeanTest extends HttpServlet {

    private EmployerManager employerManager;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Do something amazing with the Spring Bean ...
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        WebApplicationContext applicationContext = WebApplicationContextUtils.getRequiredWebApplicationContext(config.getServletContext());
        employerManager = applicationContext.getBean("business-logic.EmployerManager", EmployerManager.class);
        super.init(config);
    }

}

As you see, you can access Spring WebApplicationContext and then the desired bean by its identifier. Main disadvantage of this method is the bean identifier hardcoded into Servlet code. Especially if you are performing automatic component scan in Spring (ex. <context:component-scan base-package="[...].logic.impl" />). In this case you have two choices:

1. Define the identifier of the bean using annotations:
   

   
   @Service("business-logic.EmployerManager")
   public class DefaultEmployerManager implements EmployerManager {
      ...
   }
   

2. Use default bean identifier created by Spring in your Servlet - see: Naming autodetected components

Now relax, close your eyes, think about the refactoring the code, and all those hardcoded names which you should change by hand. It's time to forget this method my Friend, as I did. :)

Thankfully there are many young people, with open mind, who don't use the old-fashioned ways of doing things, and invent their own, as did my colleague - Bartek. Below you may find method doing the same as the above one, but based on @Autowired annotation usage.

public class BeanTest extends HttpServlet {

    @Autowired
    private EmployerManager employerManager;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Do something amazing with the Spring Bean ...
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this, config.getServletContext());
        super.init(config);
    }

}

SpringBeanAutowiringSupport will inject the appropriate Spring Beans into all your Servlet's properties marked with @Autowired annotation. That's all :) No hardcoding of bean names, no worries about future refactorings. Now relax, close your eyes, ...