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Writing your first plugin#

In this page we will disect the "Hello world" plugin project, apply editions on the code, do the packaging, deploy, and testing on a Gluu Casa installation.


Requirements for this task are the same as those listed in the introductory page except for LDAP-related stuff which is not needed. Additionally, maven will be used as build tool. If you don't want to use maven you'll need to investigate how to perform the tasks in the tool of your preference.

If you skipped "Introduction to plugin development" we strongly encourage you to check it now.


Hello world is minimalistic plugin that showcases very basic aspects of plugin development. This plugin will simply add an item to Casa users menu which in turn takes users to a separate page showing a salutation. In this page you can enter some text, execute server-side logic and update the UI back accordingly.

Download project#

Let's start by downloading the code. Hello World plugin is found inside the Gluu Casa project itself. This way you can easily check the underlying APIs and real world UI pages, particularly, the casa-shared module being of remarkable interest.

If you have git installed in your machine, issue the following command. Replace the content in the angle brackets with your Gluu Casa version (e.g. "version_3.1.6"):

$ git clone
$ git checkout <branch>

Alternatively you can download a zipped version of the project from github:

  • Visit this page and pick from the dropdown the branch matching your Casa version
  • Click on the "Clone or download" button, then on "download ZIP"
  • Extract the contents of the file to a convenient location

Generate javadocs#

It is very useful to have some apidocs at hand. Please cd to the directory where you extracted or cloned the repo and do:

$ mvn javadoc:javadoc -pl shared
$ cd plugins/helloworld
$ mvn javadoc:javadoc

It is assumed mvn (maven executable) is in your path.


Plugin directory is found in plugins/helloworld folder. As you can see, this is a standard maven project.


Let's start by disecting the build descriptor (pom.xml):

  • Identifiers and versions: At the top of the file variables and plugin.version are defined. These are key for plugin's metadata. Also we reuse those to name the artifact to be produced: note the artifactId and version tags; this means the name of the generated jar will follow the pattern: {}-{plugin.version}.

  • Assembly: We leverage the maven-assembly-plugin that allow us to generate a jar with dependencies and a suitable manifest file (see "anatomy of a plugin"). Note the <archive> section of pom.xml reuses the ID and version defined previously and also supplies extra info, being <Plugin-Class> one the most relevant.

  • Dependencies: This simple plugin just accounts for one dependency, namely the casa-shared module. This dependency is obtained from Gluu repository (see <repositories> section).

Plugin's class#

In the build descriptor, <Plugin-Class> element points us to class This class extends org.pf4j.Plugin which is a requirement of our plugin framework. A plugin project should bundle only one class of this kind.

Plugin classes can override methods of org.pf4j.Plugin (e.g. start and/or stop) if they need to do some processing upon plugin start or stop. For HelloWorld we don't need so we simply call the constructor of the superclass.


In the same package of plugin class, that is, we can find HelloWorldMenu, this is the only extension this plugin contributes. Recall from the intro page concepts that extensions are classes that implement extension points (interfaces annotated with org.pf4j.ExtensionPoint that define a set of methods of interest).

HelloWorldMenu is a class annotated with org.pf4j.Extension that implements extension point org.gluu.credmanager.extension.navigation.NavigationMenu. NavigationMenu defines a couple of methods that allow implementing classes to add items (more generally, content) to menus. Check the javadocs (in folder shared/target/site/apidocs) for a thorough description. Note that menuType is a default interface method. If it weren't present in HelloWorldMenu the same effect would be achieved.

Method getContentsUrl references a path to a page that can contain markup of any kind. It will get added to the overall menu markup you are targetting (user, admin, or auxiliary), see org.gluu.credmanager.extension.navigation.MenuType. Markup is added in order of priority (see getPriority method), the higher the value, the upper position in the menu.


All "extra" menu items are added after Casa defaults. For example, if you are targetting user menus, the 2FA menu and password reset will be shown first, those dynamically added come afterwards.

In this particular case, NavigationMenu returns the String "menu.zul" which you can find in HelloWorld dir src/main/resources/assets. Once your plugin is loaded and started in Casa, this file (and any other in assets) will be accessible under the URL https://hostname/casa/pl/hello-world-plugin/. Later, we will explain more in detail how the filesystem to URL mapping works.

Resource bundle#

As described in Anatomy of a plugin, plugins may declare one resource bundle with internationalization labels. This is a neat approach to decouple UI pages from actual text content. In folder src/main/resources/labels of plugin we find the resource bundle which consists of a single file, This contains just a couple of entries that are referenced by UI pages.

UI pages#

HelloWorld bundles a couple ZK files in src/main/resources/assets:

It contains the markup required to render this plugin menu item. Important facts about this page are:

  • Default XML namespace (xmlns) is associated to native (this is shortcut for namespace This ZK namespace is used to specify native HTML tags. This kind of elements have no components associated in the server side, thus, having the highest performance. The big majority of casa pages markup is built by using only native components.

  • z prefix is associated to the zul namespace ( This is comprised by most of standard ZK components. In examples you find in the Internet about ZK, you'll see this is used as the default namespace (no prefix). We don't follow this practice here because native namespace is the most common in Casa.

  • Expressions of the form ${...} are known as EL expressions and are useful to access data held in objects living in the server side (Java) or parameter values.

  • The css object is a Java map that contains reusable styles, menuItem being one of those. Once the key (i.e. menuItem) is looked up in the map, a set of primitive styles are obtained. These primitives are usually Tachyons rules you can find in the stylesheet at https://host/casa/styles/tachyons.min.css.

  • zkService is a managed bean of type It exposes two useful properties for writing zul templates, contextPath and appName. When writing links (a tag) in native dialect is useful to know what the root path of the application is (aka the context path). This is the preferred method instead of simply hardcoding /casa in your pages.

  • base is a parameter your page can read and contains the relative path associated to the plugin, in this case /pl/hello-world-plugin. Ultimately, the href attribute of the a tag is pointing to this plugin index.zul file.

  • labels is a Java map which can be used to access the labels defined in all resource bundles the application uses (including this plugin's).

  • The markup in this file resembles a lot how the already existing menu items of Casa were created. You are not required to build your markup this way, however it keeps it visually and functionally consistent with the rest of the application. For instance, usage of rule collapsible-menu-item allows the inner span to be hidden when the hamburguer icon on the top is pressed.


It has the contents of the page where the user is taken after clicking on this plugin's menu item. We highlight the following facts:

  • The page processing instruction sets the language to use when this page is interpreted by the rendering engine. ZK supports several languages being xul/html and xhtml the most prominent. In this case we use xhtml since the root template all Casa pages reuse is based on this language.

  • The init processing instruction tells the rendering engine to use the file at /general.zul as the template for the content to produce. This file can be found under app/src/main/webapp. general.zul is the base skeleton for most of application pages, and is based at the same time on basic.zul. The effect produced is that it surrounds the actual content with the header, left menu, and footer.


For more information on templates, check "Templating" in ZK developers reference. Note that template injection (using <template> and ` tags) don't work since this requires ZK EE.

  • index.zul defines two named contents, title and maincontent. The former contains markup that ends up being added to the HEAD section of the markup generated, the latter has the markup that will be included in the main content area of the page. You can see this happens at @insert directive found in general.zul file.

  • In general all pages are structured as in the figure below: a content heading area appearing just under the header. Below it a wrapper consisting of one or more sections. Every section can contain one or more panels whose structure depends on the specific need to cope. In your plugins try to adhere to this standard: new pages will fit neatly in current Casa design.

general structure


Use existing pages in Casa as a guide to write your own. Do not use as a first guide the actual markup generated by the browser but the .zul pages you can find under app/src/main/webapp and its subdirectories.

In addition to the above, the following are functional aspects worth to mention:

  • The class is employed as this page ViewModel.

  • A salutation is displayed: the expression to compose the actual message is ${labels.hello.user_message} ${sessionContext.user.userName} (a concatenation of an entry in the resource bundle and a value in a managed bean).

  • There is a binding of the text entered in a textbox with the class field message of the ViewModel (HelloWorldVM). This means that if text changes in the UI, message is synced with the value, and if message is changed in the Java backend, the UI will update with the proper value.

  • When the button of this page is clicked, it triggers a call to method loadOrgName in the ViewModel. This method is annotated with @Command in that Java class and changes the value of class field organizationName. The same call is triggered when enter key is pressed when the textbox has focus (see onOK attribute).

  • There is a one-way binding ("load") with regard to ViewModel's field organizationName. This means that its value can be used in the page (e.g. for display), but no syncing takes place from page to server.


Some key facts about class (the ViewModel for index.zul):

  • It has a getter/setter for the field where 2-way binding is required (i.e. message). The getter is called when the page loads the first time (resulting in the text field with empty text), and the setter is called when text is typed in the textbox by the user.

  • It has a getter for the field which is displayed only (organizationName). The getter is called upon page loading as well after server side processing occurs (like when pushing the button). This allows the value salutation be shown.

  • Every time the page is loaded, method init is called (due to the presence of annotation org.zkoss.bind.annotation.Init). In this method some initialization takes place: we obtain a reference to a managed bean using Utils.managedBean.


Being able to log statements is key for any project and Casa plugins are not an exception. You can obtain an instance of org.slf4j.Logger using getLogger method of org.slf4j.LoggerFactory (as in HelloWorldVM). slf4j is available when you include casa-shared in your project dependencies.

Here Logger-Name entry of your plugin manifest plays a key role (see file pom.xml): in your plugin any Logger associated with a class whose name is prefixed by the value of such entry will be effectively logged in Casa log file. Statements are logged using the same level as the global logging level of the application. This can be configured in the admin dashboard.

As an example, if a plugin you are writing has all its classes under com.mycompany.plugins.MyPlugin hierarchy and you obtain Logger instances using LoggerFactory.getLogger(getClass()), a good choice for Logger-Name would be com.mycompany.plugins.MyPlugin or com.mycompany.plugins. Statements won't be logged for a class com.mycompany.MyClass if Logger-Name is com.mycompany.plugins.


Let's do our first attempt to generate a jar for HelloWorld. In a command line cd to plugin directory (i.e. plugins/helloworld of Casa repo you cloned) and issue:

$ mvn clean package

This will produce a file named hello-world-plugin-0.1-jar-with-dependencies.jar. Note it follows the pattern {}-{plugin.version} we mentioned earlier. Open the file in a compression (zip) utility to inspect its composition:

+-- assets 
+------ index.zul
+------ menu.zul
+-- labels
|   +--
|   +-- extensions.idx
+-- org
    +-- gluu
        +-- casa
            +-- plugins
                +-- helloworld
                    +-- HelloWorldMenu.class
                    +-- HelloWorldPlugin.class
                    +-- HelloWorldVM.class

This resembles what we had already described in the intro page with regard to the plugin anatomy. If you have been reading in detail, no file is a stranger. Note how extensions.idx lists our single plugin extension:

# Generated by PF4J

Assets folder to URL mapping#

In the following section we will start playing around with our plugin. Before moving onto that, please notice all files you place in the assets directory of your plugin will be web accessible at URL https://hostname/casa/pl/hello-world-plugin/, this means that once deployed, if you hit https://hostname/casa/pl/hello-world-plugin/index.zul or https://hostname/casa/pl/hello-world-plugin/menu.zul in a browser you will see those ZK documents rendered as HTML content.

You can include an arbitrary structure of folders and files in assets directory and they would accessible. This is a perfect place to add javascript, images, stylesheets, etc.



Ensure your environment is aligned with respect to the requirements beforehand.

Loading HelloWorld#

Follow these steps:

  1. Login to Gluu Casa using administrator credentials: https://hostname/casa.
  2. Access the admin dashboard and select "Logging". Set the severity to TRACE
  3. Select the "Plugins" option and click on the "Add a plugin..." button
  4. Browse for the jar file generated here. After uploading completes, a page showing your plugin metadata should be shown.
  5. Click on the the "Add" button. If the operation succeeds, your plugin is considered "started". Learn more about plugin states here.
  6. The plugin will be added to the list showing basic details, including a summary of extensions detected.

Check the log#

Do a quick check of the logs. This is not needed in real production setting, but it makes sense developers familiarize with the internal steps Casa performs to onboard plugins. This may also help troubleshooting for future work.

Access plugin page#

Access the home page of Casa, you will be able to see a new link was added to user menu on the left (it's labelled "Hello world!" and has a cool accompanying icon). After clicking on it a separate page (https://hostname/casa/pl/hello-world-plugin/index.zul) is shown.

Check the app log, you will see a statement like "Hello World ViewModel inited" this is added by method init of HelloWorldVM.

The page is showing a message that includes your current user name inviting you to type something in the text box. Type anything and press the button. This will end up in the execution of loadOrgName method of HelloWorldVM. This adds a new log statement and sets the value of class member organizationName. This value is obtained after an LDAP query!.

After execution of this method, the UI is partially refreshed, which causes a new message to appear in the UI.

Unload the plugin#

  1. Access the admin dashboard and select the "Plugins" option.
  2. Press the "stop" button for the HelloWorld plugin, and then press "delete".
  3. Try hitting again https://hostname/casa/pl/hello-world-plugin/index.zul, you should see the "NOT FOUND" error.

Apply editions#

You have now a good sense of how plugins work. Now let's alter the project a bit...

  1. Edit the file src/main/resources/assets/index.zul. Remove pt3 rule from class attribute of the sections wrapper. What does pt3 mean?

  2. Just before this tag, add <z:include src="/back-home.zul" />. This will make the contents of back-home.zul (at directory app/src/main/webapp) be included. Inspect that file, what does it do?

  3. Alter the EL expressions in label tag so that the user's lastname is shown instead of username.

  4. Edit HelloWorldVM in the following way:

    Remove the line ldapService = ... in init method, then edit ldapService member by adding a WireVariable annotation like this:

    private ILdapService ldapService;

    WireVariable is an annotation of package which is a sort of equivalent for javax.inject.Inject. It allows us to reference an instance of ILdapService (see casa-shared javadocs). Usage of WireVariable has a disadvantage though: you need to know the EL name of the bean you are trying to inject.

    Specifically the injection above is equivalent to this one:

    private ILdapService ldapService;

    if the field name were myLdapService instead of ldapService, you are forced to supply the parameter in the annotation. This parameter should match the EL name of the bean you are injecting, that is, the managed bean in Casa that implements the interface ILdapService is annotated this way: javax.inject.Named("ldapService"). If the bean didn't have a Named annotation, WireVariable injection would give you a null reference.

    For the reasons above, Utils.managedBean is a safer way to go.

  5. Save changes, and repackage the project once more.

  6. Deploy again an verify all is working as expected.

Troubleshooting and testing tips#

  • First source for trouble investigation is the log file. Check your /opt/gluu/jetty/casa/logs/casa.log and read this beforehand.

  • While you get acquiantance with writing pages, you can use the z:label component to debug variable or expression values in zul. In most cases errors are caused by wrong usage of available namespaces. Locate an already existing page having a similar behaviour you desire and inspect its markup. This can save you lots of trial/error cycles. Also, it's good to work in small increments: do not attempt to write the entire page and backing Java code at once to test it thoroughly.

  • The life cycle for plugin development isn't tedious, but you can boost your performance by following the Tips for plugin development