struts2: default parameter generated by s:url tag

Question

In struts2 we use

<action name="anAction">
    <result name="success">xx.jsp</result>
</action>

to define action, and use s:url to generate a link to the action

<s:url action="anAction"></s:url>

The above s:url will output "/anAction.do".

I wonder if it's possible to let s:url generate a default URL parameter (i.e. /anAction.do?p=xxx for all links), without modifying the existing s:url tags (there are many and they are scattered). The goal is to let the parameter appear in the link for SEO purpose.

Available options can be: changing any action config, changing any struts config, even rewrite the s:url generation class.

Edit: I found that adding this to struts.xml

<constant name="struts.url.includeParams" value="get" />

partially solves my problem (as long as the initial page has ?p=xxx, all subsequent links will have it). The short-comings are obvious: the parameter will not follow a redirect action. I am still searching for more sophisticated solution.

Answer 1

I did figure out how this can be done. The steps are:

1) create a class which implements org.apache.struts2.components.UrlRenderer 2) register that class with struts object factory and it will be injected as necessary

Details? Ok.

1) For example, a subclass of ServletUrlRender might look like this:

package com.example;

import java.util.Map;

import org.apache.struts2.components.ServletUrlRenderer;
import org.apache.struts2.components.UrlProvider;

public class ParameterInjectingUrlRenderer extends ServletUrlRenderer {

    @Override
    protected void mergeRequestParameters(String value, Map<String, Object> parameters, Map<String, Object> contextParameters) {
       super.mergeRequestParameters(value, parameters, contextParameters);
       parameters.put("myParameter", "secretvalue");
    }
}

2) In struts.xml, set this class as the renderer implementation, with a line like this:

<constant name="struts.urlRenderer" value="parameterInjectingUrlRenderer" />

(In this example I'm using a Spring object factory, and value references a spring bean id. If you are not, I believe you put the fully-qualified class name).

That's it!