Hook into the rendering of a WordPress Template

Question

I have to use WordPress as some meta templating system and include some JSP snipptes which will be evaluated later with Tomcat after rendering the page statically. But naturally the JSP Code could not be interpreted by the php parser. This results in plain text strings mixed with the interpreted template parts.

Is there any way to hook into the (pre) rendering of a WordPress Template?

I need way get access the rendered template so i can strip out the JSP-Tags. Maybe wrapped between some unique tags or something else. But this ist not part of this question.

Example

<?php get_header(); ?>

<render:jsp>
    <%= request.getParameter("title") %>
</render:jsp>

<?php get_footer(); ?>

Answer 1

You can, but WP doesn't offer you the possibility to do it in a nice way, so you have to use output buffering.

Something like:

// before template is included
add_action('template_redirect', function(){

  // you can do some checks here
  // perhaps you need this only a certain page?
  if(!is_home())
    return;

  // capture output from here on...
  ob_start(function($html){

    // this function runs after the capture ends,
    // you can replace your tags here 
    $html = strtr($html, array(
      '<render:jsp>'  => '<!--',
      '</render:jsp>' => '-->',
    ));

    return $html;

  });

});

The contents of the buffer are automatically sent by PHP to the output just before the script finishes execution.