The OpenCms Content Subscription Engine

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OpenCms 8 comes with a new API for content subscription and notification of users. This is a useful feature especially in an Intranet scenario where users want to get notified about updates to important documents.

This tutorial explains how the OpenCms 8 Content Subscription Engine (CSE) provides these features. The CSE offers a range of functions to keep users informed about changes in the OpenCms content. Among this is a new API, a new database driver and taglib extensions that can be used in templates for the creation of websites.

The implementation details of the CSE are covered in this tutorial as well as use case examples for the new functions.


Basic concepts

  • The content subscription engine provides two main features:
    • Subscriptions
    • Visit tracking
  • How these features are used is not prescribed by the subscription engine
  • They are tools used by the template developer to add subscription features to their sites
  • Can be used independently from each other
  • Subscription/visit data is stored in new tables in the database
  • Subscriptions
    • Association between OpenCms users and individual VFS resources
    • Also possible for groups
    • Can be read or written using JSP tags and content collectors
  • Use case: Web site personalization
    • Users can subscribe to their favorite contents
    • The user's subscribed contents are displayed in a side bar
  • Use case: Notifications
    • Administrator subscribe users to contents which they should read
  • Visits
    • With the subscription engine, visits of a resource by users can be recorded
    • Only last visit of a user is tracked for each resource
    • Visit data can be accessed via JSP tag and collectors, too
  • Use case: Displaying list of resources which have changed since the last visit
  • Use case: Displaying different information depending on whether the user is visiting the page for the first time or not
  • The subscription engine can be either used with ADE or with the classic OpenCms template mechanism
  • Template/Formatter JSPs need to be adapted to use subscriptions or visits
  • It's up to the template developer to decide what they use subscriptions for
  • Subscriptions and visits work on the level of resources, not pages or URLs


Subscription screenshot.JPG

Using subscriptions

The <cms:usertracking> tag

  • New tag: <cms:usertracking>
    • Multi-function tag which can perform different actions
    • Used for both subscriptions and user tracking
    • Possible operations for subscriptions:
      • Subscribe user to resource
      • Unsubscribe user from resource
      • Check if a resource is subscribed to a user
  • Example for subscribing/unsubscribing to files:
<c:if test="${not empty param.action}">
  <c:when test="${param.action == 'subscribe'}">
    <cms:usertracking action="subscribe" file="${param.file}" />
  <c:when test="${param.action == 'unsubscribe'}">
    <cms:usertracking action="unsubscribe" file="${param.file}" />
  • Subscription for another user:
<cms:usertracking file="…" action="subscribe" user="${username}"/>
Possible use case: Admin wants a specific user to see a certain content in his subscriptions
  • Checking for a subscription:
<c:set var="subscribed">
 <cms:usertracking action="checksubscribed" currentuser="true" file="${sitepath}"/>
The tag will be evaluated to „true‟ or „false‟
  • Checking for subscription of a specific user:
<c:set var="subscribed">
 <cms:usertracking action="checksubscribed" username="${username}" file="${sitepath}"/>

Using collectors

  • The <cms:usertracking> tag is used for operations on a single file
  • Use the OpenCms content collector mechanism for accessing lists of contents
  • New content collector: allSubscribed
    • Used to collect subscribed resources
    • Java class: org.opencms.file.collectors.CmsSubscriptionCollector
  • Parameters are given as a '|'-separated list of key=value pairs
  • Configurable using various parameters, e.g.
    • resource: parent folder
    • includesubfolders: indicates whether subfolders should be searched
    • user: the user for which the subscribed resources should be fetched
    • currentuser: if true, gets subscribed resources for the current user
  • Example: Collecting all subscribed resources for the current user in the current site
<cms:resourceload collector="allSubscribed" param="resource=/|currentuser=true|includesubfolders=true|mode=all">
 <cms:resourceaccess var="item" />
  • Parameter "mode" has three possible values:
    • all: find subscribed resources
    • unvisited: finds subscribed resources unvisited since last change
    • visited: finds subscribed resources visited since last change
<cms:resourceload collector="allSubscribed" param="resource=/|currentuser=true|includesubfolders=true|mode=all">
 <cms:resourceaccess var="item" />
  • New tags <cms:resourceload>, <cms:resourceaccess>
  • Like <cms:contentload> and <cms:contentaccess>, but only load resource information, not contents
  • Needed because resources which aren't normal XML contents can be subscribed
  • Faster, too, if you only need e.g. the title property or resource name –does not need to parse XML files
  • ${item} is a Java bean of type org.opencms.jsp.util.CmsJspResourceAccessBean

Using visits

Tracking user visits

  • User tracking functionality:
    • Marking a page as visited by a given user
    • Checking whether a user has visited a page
    • Finding visited resources
  • Done via the <cms:usertracking> tag and content collectors
    • Special handling for binary files needed
  • Example: Mark a resource as visited by the current user
<cms:usertracking action="visit" file="${filepath}"/>
  • Example: Mark visit by a specific user
<cms:usertracking action="visit" user="User" file="${filepath}" />
  • Example: Check if a user has visited a resource
<cms:usertracking action="checkvisited" currentuser="true" file="${filepath}" />
Will evaluate to 'true' or 'false'
  • New collector: allVisited
    • Java class: org.opencms.file.collectors.CmsSubscriptionCollector
  • Collects visited resources, filtered by user, folder and time range
  • Visited resources for current user:
    • currentuser=true
  • Visited resources for user Username:
    • user=Username
  • Selecting by time range:
    • Parameters: daysfrom, daysto
    • Values: Range of days back from the current time for which the visited resources should be returned
    • Example: Resources visited by the current user in the last two days
  • daysfrom=2|daysto=0|currentuser=true
  • Selecting by folder:
    • resource=/folder/
  • Selecting by folder or subfolders:
    • resource=/folder/|includesubfolders=true

Handling binary files

  • This works only for structured contents
  • Special resource init handler for binary files
  • Intercepts direct requests to resources and marks them as visited
  • Must be configured in opencms-system.xml:
 <resourceinithandler class="org.opencms.db.CmsUserTrackingResourceHandler"/>
  • Will mark certain files as visited by a user if their URL is requested by them
  • You also have to set the export property to false so that the files will not be statically exported
  • Controlled by the property usertracking.mark
  • Values:
    • online: opened resources will only be marked as visited in the Online project
    • true: opened resources will always be marked
    • false(or not set): resources will not be marked
  • Why not do this for all files?
    • Rendered pages consist of multiple resources
    • Especially now with Advanced Direct Edit (container pages containing multiple elements)
    • The resource which is directly requested is not necessarily the resource which should be marked as visited
    • The <cms:usertracking> tag gives the template developer more control than the resource init handler

Further topics


  • Add entry to opencms-system.xml:
    • <subscriptionmanager enabled="true" poolname="default" maxvisited="500" />
    • Add it as the last sub-element of the <system> element
  • enabled: enables or disables the subscription engine
  • maxvisited: the maximum number of visited resources stored for a given resource
  • poolname: the database pool used to access the subscription information
    • Important when using a cluster, because data should be stored in a central location

Preventing browser caching

  • Subscriptions/visits will not work correctly if the user's browser caches pages on which the <cms:usertracking> tag or collectors are used
  • Insert <cms:nocache> JSP tag into main template JSP before any output is written:
<%@pagebuffer="none" session="false" taglibs="c,cms,fn" %><cms:nocache/>
  • This will tell the browser to not cache pages

The Java API

  • Everything you can do with the collectors or tags, you can do with the Java API
  • org.opencms.db.CmsSubscriptionManager
  • Access via org.opencms.main.OpenCms
  • Example: reading all subscribed resources for a user
CmsObject cms= …;
CmsUser user= …;
List<CmsResource> resources= OpenCms.getSubscriptionManager().
readAllSubscribedResources(cms, user);
  • Also offers some additional functionality
  • Example: reading the last visit date
CmsObject cms= …;
CmsUser user= …;
CmsResource resource= …;
long lastVisited= OpenCms.getSubscriptionManager().getDateLastVisitedBy(cms, user, resource);
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