propleme with the injection of dependence of spring

Question

For the project that we create during my formation we use spring to make dependency injection.

we have a servlet-context.xml file with the following configuration:

<context:component-scan base-package="fr.autoquiz3000" />

I created several controllers and I have no problem injecting the dao for example:

package fr.autoquiz3000;

@Controller
@RequestMapping("/public")
public class PublicController {

    @Autowired
    private UserDao uDao;

    @GetMapping("/connection")
    public ModelAndView getConnection() {
        return new ModelAndView("public/viewConnexion");
    }

but I try to create a filter with a dao like this:

package fr.autoquiz3000;

@Component
public class CountQuizStudent implements Filter {

    @Autowired
    private QuizToDoDao qtdDao;

and I have this error:

qtdDao= null
java.lang.NullPointerException
at fr.autoquiz3000.CountQuizStudent.doFilter(CountQuizStudent.java:41)

Someone could explain to me what I'm doing wrong!

thank you!

Answer 1

For filters override init method and set Spring beans there:

@Override
public void init(FilterConfig filterConfig) throws ServletException {
    WebApplicationContext springContext =
        WebApplicationContextUtils.getWebApplicationContext(filterConfig.getServletContext());
    userDao = springContext.getBean(UserDao.class);
}

or use DelegatingFilterProxy:

<filter>
    <filter-name>yourFilter</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
    <filter-name>yourFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>


@Component("yourFilter")
public class YourFilter implements Filter { 
    // auto wiring available as it's just Spring Bean
}