Elliott’s Development Blog

Getting the Expected Results for GetCurrentTemplatePath() in a Custom Tag.

July 17, 2007 on 5:43 pm | In Programming, Java, Adobe, ColdFusion |

While working on the template system used for the conference websites I ran across a problem where I needed the path to the template that called a custom tag. The first thing I tried was getCurrentTemplatePath() thinking that it might return that since the documentation makes no mention of custom tags. Instead, however, the function returns the path to the custom tag itself.

Ben Nadel noticed some of this odd behavior as well.

I spent a long time trying to figure out how to get the caller template path, including what Ben did which was to add a special function to the caller scope.

<cfscript>
function getCallerTemplatePath() {
    return getCurrentTemplatePath();
}
caller.getCallerTemplatePath = getCallerTemplatePath;
path = caller.getCallerTemplatePath();
</cfscript>

This doesn’t work though. Instead I still got the template path of the custom tag!

I dug around in the PageContext (which is returned from getPageContext() if you’re not familiar) with no luck and finally gave up resorting to this…

/**
    Monumental hack, but the only way I could figure out how to do
    a getCurrentTemplatePath() like call that resolves to the page
    that called this custom tag.
*/
function getCallerTemplatePath() {
    try {
       error;
    } catch( any cfcatch ) {
        return cfcatch.tagContext[3].template;
    }
}

Which worked but really felt like a hack since it means throwing an exception on every request. So I kept an eye out as I dug around in the internals of the CF engine for various other things, and today I was rewarded with an awesome solution.

/** Gets the path to the page that called this custom tag. */
function getCallerTemplatePath() {
    var field = getMetaData(caller).getDeclaredField("pageContext");
    field.setAccessible(true);
    return field.get(caller).getPage().getCurrentTemplatePath();
}

Now to get at why and how this kind of thing works…

Inside the ColdFusion runtime the foundation unit for all scripts, components and tags is the coldfusion.runtime.CFPage object, and the getCurrentTemplatePath() function is really identical to…

function getCurrentTemplatePath() {
    return getPageContext().getPage().getCurrentTemplatePath();
}

After realizing this it dawned on me that the custom tags, cfcs, and pages all have their own PageContext and Page objects, and as such the template path is going to be different, or rather bound, to the page in which the function is called from, not where it’s defined.

Knowing this I was able to grab the page context out of the caller scope, which is the page context of the caller, and not the current page, and use that to get the current template path of the page for which that page context operates.

Also, for those who aren’t familiar, the getMetaData() function can be used to return the java.lang.Class instance for most objects you wouldn’t normally be able to call getClass() on in ColdFusion. For instance you can call getMetaData(variables).getName() and you’ll get coldfusion.runtime.VariableScope.

Doing this really made my code feel less icky, so I hope this is useful to someone else.

(PS, Tested and works on CF6+ and CF7+, anyone have CF8?)