Re: page modification, not just decoration

Well actually it *is* an extensible HTML parser :)

To do this, you can extend SiteMesh's HTML parser and add a new tag rule for processing <a> tags.

public class MyParser extends HTMLPageParser {

  // override default rulest
  protected void addUserDefinedRules(State html, PageBuilder page) {
    super.addUserDefinedRules(html, page);

    // Add a rule.
    // Rules allow the parser to do custom things when encountering HTML tags.
    html.addRule(new LinkRewritingRule()); // see below
  }
}

class LinkRewritingRule extends BasicRule {

      public LinkRewritingRule() {
        super("a"); // Handles all <a> tags.
      }

      public void process(Tag tag) { // Called when parser encounters <a>
        CustomTag newTag = new CustomTag(tag); // Allows tag modification
       
        // modify href attribute
        boolean caseSensitive = false; // allow HREF or href or HrEf
        String oldHref = newTag.getAttributeValue("href", caseSensitive);
        if (oldHref != null) {
          String newHref = // do something;
          newTag.setAttributeValue("href", caseSensitive, newHref);
        }
       
        // write the new tag bag to the page
        newTag.writeTo (currentBuffer());
      }
    }
}

To enable this, edit sitemesh.xml and update the <page-parser> tag to point to your new parser class.

Your decorator is a standard executable page (probably a JSP or Velocity page), so you can include code to output the necessary meta tags there (which can look at the URI).

You could create another tag rule, that looks out for <script src> tags and adds them to the page properties. (If you've ever accessed the meta tag properties from a SiteMesh page this works the same way):

class ScriptSrcExtractingRule extends BasicRule {
      private PageBuilder page;

      public ScriptSrcExtractingRule(PageBuilder page) {
        super("script"); // Handles all <script> tags.
        this.page = page;
      }

      public void process(Tag tag) { // Called when parser encounters <script>
        String src = newTag.getAttributeValue("src", caseSensitive);
        if (src != null) {
          // we found a <script src>. Make it available as a page property.
          page.addProperty("script." + src);
        }
        tag.writeTo(currentBuffer()); // ensure original <script> tag is still written out.
      }
    }
}

Add this to your parser class (above).

Then from decorators, you can do:

<decorator:usePage id="myPage" />
<% if (!myPage.hasProperty("script.something.js")) { %>
<script src="something.js"></script>
<% } %>

cheers
-Joe