Spring injection in Filter implementation mapped in web.xml

Question

web.xml:

<filter>
    <filter-name>myFilter</filter-name>
    <filter-class>com.mypackage.MyFilter</filter-class>
</filter>

<filter-mapping>
    <filter-name>myFilter</filter-name>
    <url-pattern>/myFilterPattern/*</url-pattern>
</filter-mapping>

MyFilter:

public class MyFilter implements Filter {

    @Autowired
    InjectedBean someInjectedBean;

However, when intercepting /myFilterPattern/* requests, someInjectedBean in MyFilter.doFilter(...) is still null, meaning it has not been injected. The same bean (InjectedBean) is injected fine in other context components that are not referenced in web.xml.

Is it because container filtering takes place outside the Spring context? Is there any way to have Spring injection in Filter implementation mapped in web.xml?

score 4 · Accepted Answer · edited Jul 07 '20 at 09:03

4

Since Filter is not a spring bean(it is a web component) the injections won't work inside them. Springs wont inject inside web component.

use a DelegatingFilterProxy, this is a filter implementation that takes a springbean name as init param and delegates the filter request to that bean.

<filter>
  <filter-name>myFilter</filter-name>
  <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
  <init-param>
    <param-name>targetBeanName</param-name>
    <param-value>myFilterBean</param-value>
  </init-param>
</filter>

<filter-mapping>
  <filter-name>myFilter</filter-name>
  <url-pattern>/myFilterPattern/*</url-pattern>
</filter-mapping>

And create a Bean with name myFilterBean in your spring context.

public class MyFilter extends GenericFilterBean {

    @Autowired
    InjectedBean someInjectedBean;
 
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
      FilterChain chain) throws IOException, ServletException {
        chain.doFilter(request, response);
    }
}

edited Jul 07 '20 at 09:03

Adam Kučera

424
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answered May 03 '17 at 21:03

Praneeth Ramesh

3,434
1
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34

2

did you mean "create a Bean with name **myFilterBean** in your spring context" ? – amphibient May 03 '17 at 21:08
Yes Create a bean with name myFilterBean of type MyFilter. MyFilter can extend GenericFilterBean. – Praneeth Ramesh May 03 '17 at 21:10
what do you think the scope of that bean should be in the context ? session ? – amphibient May 03 '17 at 21:11
1

It can be singleton. Filters are created once at the app startup. – Praneeth Ramesh May 03 '17 at 21:20
I did all of this and the container renders a blank page. it doesn't go into `MyFilter` – amphibient May 03 '17 at 21:29
Check the server logs. It should have thrown some error.? – Praneeth Ramesh May 03 '17 at 21:31
nvrmnd -- i had the bean session scoped. changed to singleton and it works – amphibient May 03 '17 at 21:32

SarangRN · Answer 2 · 2022-02-04T16:11:30.593

One more solution if you are using spring security and extending the OncePerRequestFilter

@Component
public class CustomAuthorizationFilter extends OncePerRequestFilter{

    @Autowired
    ResourceConfig resourceConfig;

    public CustomAuthorizationFilter() {
            SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);
    }
//...your code

its important to pull the details from resourceConfig in doFilterInternal block only so you will get values else you may end up at null pointer exception.

Spring injection in Filter implementation mapped in web.xml

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