Unable to autowire the service inside my authentication filter in Spring

Question

I am trying to authenticate user by token, But when i try to auto wire one my services inside the AuthenticationTokenProcessingFilter i get null pointer excepti

Answer 1

You cannot use dependency injection from a filter out of the box. Although you are using GenericFilterBean your Servlet Filter is not managed by spring. As noted by the javadocs

This generic filter base class has no dependency on the Spring org.springframework.context.ApplicationContext concept. Filters usually don't load their own context but rather access service beans from the Spring root application context, accessible via the filter's ServletContext (see org.springframework.web.context.support.WebApplicationContextUtils).

In plain English we cannot expect spring to inject the service, but we can lazy set it on the first call. E.g.

public class AuthenticationTokenProcessingFilter extends GenericFilterBean {
    private MyServices service;
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        if(service==null){
            ServletContext servletContext = request.getServletContext();
            WebApplicationContext webApplicationContext = WebApplicationContextUtils.getWebApplicationContext(servletContext);
            service = webApplicationContext.getBean(MyServices.class);
        }
        your code ...    
    }

}