ExtendingTheAPI

With ResponseHeaderFilter, writing your own custom implementation for applying the rules is very easy. Many a times, you may need to apply response headers based on the request or response. The ResponseHeaderFilter takes charge of performing the match for a particular mapping (and this functionality cannot be extended). Once a particular <mapping> is found to be a match, your processor class will be invoked to implement the rules in the response headers.

You may define a processor at the root level in your config, e.g <response-header-mapper processorClass="com.foo.YourClass"> ... </response-header-mapper> the class specified above would be applicable for all the <mapping>'s in your file. If you need an overriding behavior for a particular mapping, you can define a processorClass attribute for your <mapping>, e.g <response-header-mapper processorClass="com.foo.YourClass"> <mapping url="(.*).js" processorClass="com.foo.YourClassForThisMapping"> ... </mapping> ... </response-header-mapper>

And, yes writing a processor class is very simple. All you need to do is to implement the com.avlesh.web.filter.responseheaderfilter.MappingProcessor interface. This is how a typical MappingProcessor implementation would look like: ``` package com.foo;

import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.util.List;

public class SimpleMappingProcessor implements MappingProcessor { public void preProcess(HttpServletRequest request, HttpServletResponse response, Mapping applicableMapping) { }

public void applyHeaders(HttpServletRequest request, HttpServletResponse response, List responseHeaders, Mapping applicableMapping) { for(Mapping.ResponseHeader responseHeader : responseHeaders){ response.setHeader(responseHeader.getResponseHeaderKey(), responseHeader.getResponseHeaderValue()); } }

public void postProcess(HttpServletRequest request, HttpServletResponse response, Mapping applicableMapping) { } } ``` The interesting pieces are the preProcess and `postProcess` methods. These are called just before and after the `applyHeaders` is called by the Filter, when a match happens. In all the above methods, other than the `request` and `response`, you'll also have access to the Mapping for this particular url as specified in the config.