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 ...    
    }

}

Answer 2

I just made it work by adding

SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);

I am unsure why we should do this even when i tried adding explicit qualifier. and now the code looks like

public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

        SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);

        @SuppressWarnings("unchecked")
        Map<String, String[]> parms = request.getParameterMap();

        if (parms.containsKey("token")) {

Answer 3

I am late to the party but this solution worked for me.

Add a ContextLoaderListener in web.xml. applicationContext can have dependency beans.

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/applicationContext.xml</param-value>
</context-param>

Then add in MyFilter SpringBeanAutowiringSupport processInjectionBasedOnServletContext which will add the webapplicationcontext into the filter which will add all the dependencies.

@Component
public class MyFilter implements Filter {

    @Autowired
    @Qualifier("userSessionServiceImpl")
    private UserSessionService userSessionServiceImpl;

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain 
    chain) throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) req;
        if (userSessionServiceImpl == null) {
            ServletContext context = httpRequest.getSession().getServletContext();
        SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this, context);
    }

       .... (for brevity)
    }

}

Answer 4

If your filter class extends GenericFilterBean you can get a reference to a bean in your app context this way:

public void initFilterBean() throws ServletException {

@Override
public void initFilterBean() throws ServletException {

        WebApplicationContext webApplicationContext =
            WebApplicationContextUtils.getWebApplicationContext(getServletContext());
        //reference to bean from app context
        yourBeanToInject = webApplicationContext.getBean(yourBeanToInject.class);

        //do something with your bean
        propertyValue = yourBeanToInject.getValue("propertyName");
}

And here is less explicit way for those who doesn't like hardcoding bean names or need to inject more than one bean reference into the filter:

@Autowired
private YourBeanToInject yourBeanToInject;

@Override
public void initFilterBean() throws ServletException{

    SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this, getServletContext());

    //do something with your bean
    propertyValue = yourBeanToInject.getValue("propertyName");
}

Answer 5

You can configure your bean filter and pass as a parameter whatever you need. I know out of Spring context where the filter it is, you cannot get the dependency injection that the auto-scan of spring does. But not 100% sure if there´s a fancy annotation that you can put in your filter to do some magic stuff

   <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>

and then inject bean in the spring.xml

  <bean id="YourFilter" class="com.YourFilter">
     <property name="param">
        <value>values</value>
     </property>
  </bean>

Answer 6

It's an old enough question, but I'll add my answer for those who like me google this issue.

You must inherit your filter from GenericFilterBean and mark it as a Spring @Component

@Component
public class MyFilter extends GenericFilterBean {

    @Autowired
    private MyComponent myComponent;

 //implementation

}

And then register it in Spring context:

@Configuration
public class MyFilterConfigurerAdapter extends WebMvcConfigurerAdapter {

    @Autowired
    private MyFilter myFilter;

    @Bean
    public FilterRegistrationBean myFilterRegistrationBean() {
        FilterRegistrationBean regBean = new FilterRegistrationBean();
        regBean.setFilter(myFilter);
        regBean.setOrder(1);
        regBean.addUrlPatterns("/myFilteredURLPattern");

        return regBean;
    }
}

This properly autowires your components in the filter.