在另一个过滤器中调用servlet过滤器包装器

Question

Incorporate an external filter in the servlet web app by creating a wrapper filter.

A third party filter needs to be included in my application and needs to be invoked /bypassed dynamically depending on some logic. I have created a wrapper filter for the ThirdpartyFilter , but not sure how to invoke this from the wrapper class

final class ThirdPartyFilter implements Filter{

@Override
public void init(@SuppressWarnings("hiding") FilterConfig filterConfig) throws ServletException {
   this.filterConfig = filterConfig;
}

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException  {
    // Some validations here and then call the next filter in the  chain
    }
}

class MyWrapperFilter implements Filter
{

    private ThirdPartyFilter thirdPartyFilter 

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        thirdPartyFilter  = new ThirdPartyFilter(); 
        // Not sure if this is the right way to instantiate the filter
    }

   @Override
   public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException  
   {
       if(thirdPartyfilterFlag == true) {
          thirdPartyFilter.doFilter(request, response)
       }
       else
       {
           filterChain.doFilter(request, response)
       }
   }
}

The issue I am facing is instantiating the ThridPartyFilter from the wrapper.

What's the right way to instantiate this filter ?

Answer 1

I'm not sure if it's the right way to instantiate the ThirdPartyFilter, as the filter configs are usually taken care by the container..

FilterConfig just gives you to access the configuration setting you defined in the <filter> section in web.xml for that filter such that you can access these setting right after the container initialises that Filter.

But now you are programatically instantiating ThirdPartyFilter which means you are in total control of how to create it. It is just a matter if you want to externalise the configuration of ThirdPartyFilter to MyWrapperFilter 's <filter> section in web.xml . If not , you can always pass the configuration parameter through the constructor of ThirdPartyFilter when creating it.

So I don't see any problems of your codes provided that you initialises ThirdPartyFilter correctly. Just a matter of whether you want to externalise its configuration (if it has) to web.xml