Skip to main content

CWA Navigation Custom Tag

Normally with Tridion, we do navigation as a transformation between a navigation XML with an XSLT stylesheet. We plug some parameters into this transformation in order to highlight the current context.

In CWA (Content Web Application) terms, this approach still applies only with some modification. Namely, the XML and XSLT are usually both published to the CD (Content Delivery) database. This setup implies that we need a special way or reading the XML/XSLT, prior to performing the actual transformation. To this respect, I created a custom Java tag CwaTransformXml that first ensures the XML and XSLT files are extracted from the CD DB and serialized as files on the file system, then second, it performs the XSLT transformation.

CwaTransformXml has the following attributes:
  • xml - the XML file path;
  • xslt - the XSLT file path;
  • paramName - the name of the parameter to pass into the transformation;
  • paramValue - the value of the parameter;
  • out - the variable name to set in PageContext holding the result of the transformation;

Moreover, the tag caches the XML DOM document and the XSLT Template into the application scope, such that they don't need be parsed and recreated with every tag call. Also the output of the transformation can be cached in the PageContext, such that it can be reused on the same page.

    <t:CwaTransformXml xml="/en/system/nav.xml" xslt="/en/system/main.xslt"
        paramName="CurrentPage" paramValue="tcm:2-3-64"/>

The main tag logic is the following:

public int doStartTag() throws JspException {
    try {
        Document xmlDom = (Document) CacheUtils.getFromCache(xml, pageContext, cache);
        DOMSource domSource = new DOMSource(xmlDom);
        Templates templates = (Templates) CacheUtils.getFromCache(xslt, pageContext, cache);

        Transformer transformer = templates.newTransformer();

        if (out == null) {
            transformer.transform(domSource, new StreamResult(pageContext.getOut()));
        } else {
            StringWriter writer = new StringWriter();
            transformer.transform(domSource, new StreamResult(writer));
            pageContext.setAttribute(out, writer.toString());
    } catch (Exception e) {
        throw new JspException(e);

    return SKIP_BODY;

The method CacheUtils.getFromCache() makes sure the path passed to it is retrieved from the CD DB and serialized to the file system (it is using CWA's class PageFileDistributionController), parses the XML DOM (or XSLT Templates object), places it into the application scope cache, then retrieves the actual DOM/Templates object.

public static Object getFromCache(String name, PageContext pageContext, long cache) {
    CacheEntry cacheEntry = (CacheEntry) pageContext.getAttribute(name,

    if (cacheEntry == null || System.currentTimeMillis() > cacheEntry.getTtl()) {
        cacheEntry = setInCache(name, cacheEntry, pageContext, cache);

    return cacheEntry.getItem();

private static synchronized CacheEntry setInCache(String name, CacheEntry cacheEntry,
        PageContext pageContext, long cache) {
    long currentTimeMillis = System.currentTimeMillis();

    if (cacheEntry == null) {
        cacheEntry = new CacheEntry(0, null);
        pageContext.setAttribute(name, cacheEntry, PageContext.APPLICATION_SCOPE);

    if (currentTimeMillis > cacheEntry.getTtl()) {
        PageFileDistributionController controller =
        ServletContext servletContext = pageContext.getServletContext();
        HttpServletRequest request = (HttpServletRequest) pageContext.getRequest();
        File file = controller.processPage(servletContext, request, name);

        String nameLower = name.toLowerCase();
        Object item = null;
        if (nameLower.endsWith(".xslt") || nameLower.endsWith(".xsl")) {
            Source source = new StreamSource(file);
            item = transformerFactory.newTemplates(source);
        } else if (name.endsWith(".xml")) {
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            item = documentBuilder.parse(file);

        cacheEntry.setTtl(currentTimeMillis + cache);

    return cacheEntry;

Where CacheEntry class is just a POJO holding the following members:

    private long ttl;
    private Object item;


Popular posts from this blog

Running sp_updatestats on AWS RDS database

Part of the maintenance tasks that I perform on a MSSQL Content Manager database is to run stored procedure sp_updatestats . exec sp_updatestats However, that is not supported on an AWS RDS instance. The error message below indicates that only the sa  account can perform this: Msg 15247 , Level 16 , State 1 , Procedure sp_updatestats, Line 15 [Batch Start Line 0 ] User does not have permission to perform this action. Instead there are several posts that suggest using UPDATE STATISTICS instead: I stumbled upon the following post from 2008 (!!!), , which describes a way to wrap the call to sp_updatestats and execute it under a different user: create procedure dbo.sp_updstats with execute as 'dbo' as

Debugging a Tridion 2011 Event System

OK, so you wrote your Tridion Event System. Now it's time to debug it. I know this is a hypothetical situtation -- your code never needs any kind of debugging ;) but indulge me... Recently, Alvin Reyes ( @nivlong ) blogged about being difficult to know how exactly to debug a Tridion Event System. More exactly, the question was " What process do I attach to for debugging even system code? ". Unfortunately, there is no simple or generic answer for it. Different events are fired by different Tridion CM modules. These modules run as different programs (or services) or run inside other programs (e.g. IIS). This means that you will need to monitor (or debug) different processes, based on which events your code handles. So the usual suspects are: dllhost.exe (or dllhost3g.exe ) - running as the MTSUser is the SDL Tridion Content Manager COM+ application and it fires events on generic TOM objects (e.g. events based on Tridion.ContentManager.Extensibility.Events.CrudEven

Content Delivery Monitoring in AWS with CloudWatch

This post describes a way of monitoring a Tridion 9 combined Deployer by sending the health checks into a custom metric in CloudWatch in AWS. The same approach can also be used for other Content Delivery services. Once the metric is available in CloudWatch, we can create alarms in case the service errors out or becomes unresponsive. The overall architecture is as follows: Content Delivery service sends heartbeat (or exposes HTTP endpoint) for monitoring Monitoring Agent checks heartbeat (or HTTP health check) regularly and stores health state AWS lambda function: runs regularly reads the health state from Monitoring Agent pushes custom metrics into CloudWatch I am running the Deployer ( installation docs ) and Monitoring Agent ( installation docs ) on a t2.medium EC2 instance running CentOS on which I also installed the Systems Manager Agent (SSM Agent) ( installation docs ). In my case I have a combined Deployer that I want to monitor. This consists of an Endpoint and a