Extending the GlassFish v3 Prelude Administration Console

Today, the GlassFish community is launching GlassFish v3 Prelude (Release Notes and Quick Start Guide). If you are not familiar with what Prelude is, here is a short write up giving the high level details. In this article, I'd like to focus on the third bullet there, "CLI and administration console extendibility." Specifically, we'll look at what it takes to create a plugin that will extend GlassFish v3's Administration Console.

Table of Contents

Creating a plugin is really quite simple. The bare minimum is one Java class, a ConsoleProvider, and one XML config file, console-config.xml.

The Java Class

The Java class is very simple. It must implement the ConsoleProvider interface, which will require one method, getConfiguration, and it must be annotated with the HK2 annotation, @Service:
@Service
public class ConsolePluginExample implements ConsoleProvider {
    public URL getConfiguration() {
        return null;
    }
}
Despite its apparent simplicity, this class does a couple of things for us. By implementing the Interface, of course, it gives the Plugin service a type it knows about. By using the @Service annotation, the Plugin service will able to locate this plugin (and any others in the system) by asking HK2 for all the ConsoleProviders it knows about. But what about that getConfiguration() method? That method tells the Plugin service where to find the plugin's configuration file. Unless you put that in a non-standard location, this implementation is what you will see. If, however, you would like to move or rename the file, then this method will return a URL to that file.

The Config File

So that defines the plugin for the console, but how do we make it do anything interesting? For that, we need to take a look at /META-INF/admingui/console-plugin.xml:
<?xml version="1.0" encoding="UTF-8"?>

<console-config id="console-plugin-example">
    <integration-point  id="tabtestTreeNode"
                        type="org.glassfish.admingui:treeNode"
                        priority="40"
                        parentId="Resources"
                        content="treeNode.jsf" />
    <integration-point  id="tab2"
                        type="org.glassfish.admingui:tab"
                        priority="22"
                        parentId="jvmSettings"
                        content="newTab2.jsf" />
    <integration-point  id="tab1"
                        type="org.glassfish.admingui:tab"
                        priority="28"
                        parentId="serverInstTabs"
                        content="newTab1.jsf" />
</console-config>
This file does two things: it gives a name for the plugin, "console-plugin-example," and defines a number of integration points, which are the really interesting part here.

Integration Points

An integration point defines a small, discrete bit of content to be included in the console, providing information about what it is and where it should go. Let's take a look at each piece of the integration point definiton.

Integration Type

Each integration-point element has several important pieces. The first is the ID. This must be unique for the current plugin. Next is the type. This describes the type of content we want to insert via this integration point. The admin console defines several integration point types:
Integration Type Description Screen Shot
org.glassfish.admingui:applications This integration type allows a plugin to add itself to the list of managed applications (e.g, enterprise, web, etc). This screen shot shows how the web plugin adds the "Web Application" link. The applications start page
org.glassfish.admingui:commonTask This type allows users to add entries to the Common Tasks page. The implementation of this type is a good example of how flexible an integration type can be. With this, plugin authors can add common tasks to existing sections (as the web plugin does) or create a new section (as the updatecenter plugin does). The Common Tasks Page
org.glassfish.admingui:configuration Like the applications type, this type allows a plugin author to add modules to the configuration start page. The configuration start page
org.glassfish.admingui:mastheadStatusArea This type allows the user to add content to the status area of the masthead, which is the area in the header right below the product name (see screenshots). Multiple plugins are allowed to use this integration type, with entries being list left to right, based on priority (see below). The masthead status area
org.glassfish.admingui:resources This type allows a plugin author to add modules to the resources start page. The resources start page
org.glassfish.admingui:serverInstTab This integration type allows a plugin author to create a new tab on the Application Server page, or to add content to an existing tab. In this screen shot, the web plugin adds the Monitoring tab to the main tab set, as well three tabs to the newly added Monitoring tab. The server instance tabset
org.glassfish.admingui:treeNode This integration point allows plugins to add nodes to the navigation tree. The nodes can be added either to the root, or to any other node in the tree. In this screen shot, we can see how the web plugin added the "Web Applications" node to "Applications,", and the "Web Container" and "Monitoring" nodes to "Configuration." The navigation tree

Plugin Priority

The next attribute is priority. This attribute controls the order in which integration points are included, with the lower numbers coming first (It might be best to think of this as "order" rather than "priority," despite the name).

Parent ID

The next attribute is parentId. This tells the plugin service to which component to parent the included content. Using our example above, the integration point tabtestTreeNode will be a child of the component whose ID is Resources.

Plugin Content

Finally, the content attribute tells the plugin service where to find the content of the integration point. This value is typically the path, relative to the plugin's root, to the file that defines the content, which is simply a JSF page. In our example, we point to "treeNode.jsf." In a Maven project, this file would be in src/main/resources, and would be in the root directory of the resulting jar. This example file's contents look like this:
<sun:treeNode id="tabtest"
              text="Test Node #1"
              url="tabtest/jdbcLists.jsf"
              target="main"
              imageURL="resource/images/instance.gif" />
<sun:treeNode id="tabtest2"
              text="Test Node #2"
              url="tabtest/jdbcLists.jsf"
              target="main"
              imageURL="resource/images/instance.gif" >
</sun:treeNode>
The contents, of course, will vary depending on the plugins needs, and the type of the integration point, but, as you can see, this is just a snippet of JSF markup, which, in this case, defines two sun:treeNodes that will be inserted into the navigation tree.

Defining the Plugin Content

At this point, we've created the plugin. We've defined the integration points and specified their contents. If that's all a plugin needed to do, we'd be done, but it's not, so we aren't. :) Once you have the UI elements specified and integrated with the console, you have to be able to make those components display data, perform actions, etc. From this perspective, the plugin is just a normal JavaServer Faces application. Given the architecture of the GlassFish v3 Prelude Administration Console, a plugin author has two options: the normal JSF managed bean approach, or the JSFTemplating events/handlers approach. JSF managed beans are a well understood and documented approach, but the same can't be said about JSFTemplating Handlers and events. While an exhaustive discussion is outside the scope of this article, I'd like to offer at least a cursory introduction.

JSFTemplating Events

JSFTemplating provides a number of events that much more finely-grained than the standard JavaServer Faces lifecycle phases. There are a number of events, but the ones of interest here are (for more information, please see the JSFTemplating site):
Event(s) Description
beforeCreate/afterCreate This event fires before/after a component is created. It fires once per view, so, as long as the user stays on the same page, this event will not fire over and over.
beforeEncode/afterEncode This event fires before/after a component is rendered. Since this is at render time, this event fires every time the page is requested, so care should be taken in handling expensive operations in this event.
initPage This event fires everytime the page is requested. As with beforeEncode/afterEncode, care should be taken in handling expensive operations in this event.
command This event is for ActionSource components only and fires when the UICommand component is clicked.

JSFTemplating Handlers

To attach a handler to an event, using JSFTemplating's "template" syntax, one would do something like this:
<sun:button id="button" text="Push Me!">
<!command
    executeSomeBusinessLogic(amount="5.25", result=>$pageSession{businessLogicResult});
/>
</sun:button>
This creates a sun:button and attaches the Handler executeSomeBusinessLogic to button. When the button is clicked, the Handler is called, with the input variable amount being set to 5. After execution, the value of the Handler's output variable result is assigned a page-scoped variable called businessLogicResult, which can be referenced on the page using the EL expression #{businessLogicResult} or #{pageSession.businessLogicResult}. The Handler, executeSomeBusinessLogic might look like this:
    @Handler(id="executeSomeBusinessLogic",
        input = {
            @HandlerInput(name="amount", type=Double.class, required=true)
        },
        output= {
            @HandlerOutput(name="result", type=String.class)
        }
    )
    public static void myBusinessLogicMethod (HandlerContext handlerContext) {
        Double amount = (Double)handlerContext.getInputValue("amount");
        // Do some work.
        //     Get a reference to some external server
        //     Perform all calculations locally
        //     Whatever you need...
        handlerContext.setOutputValue("result", "Some string built from the business logic.");
    }
There are several things to note. First, the annotation defines the id by which we reference the Handler (executeSomeBusinessLogic) and it need not match the actual method name. Second, we have one input, amount which must be a Double, and is required. If it is not provided, an Exception will be thrown. Third, a single output variable, result of type String is returned. Last, the method must be public static void and must take a single parameter of type HandlerContext. Inside the method, we extract the input parameter using HandlerContext.getInputValue() and cast it to the expected type. When we reach this point in the code, we can cast with out worrying about ClassCastExceptions, as JSFTemplating insures that the type is correct. Since null could be a valid value, though, the Handler must perform null value checking as appropriate. Next the Handler performs the business logic, whether it does it internally or delegates to another object, be it local or remote, then sets the value of the output variable, result. The JSFTemplating event and Handler mechanism is, conceptually, a very simple, yet very powerful mechanism, of which the GlassFish v3 Prelude Administration Console makes heavy (and exclusive) use.

Summary

And that's all there is to writing a plugin for the GlassFish v3 Prelude Administration Console: one simple class, an XML config file, a few managed beans or Handlers, and just a few JSF markup files as necessary for your plugin. These simple building blocks make it extremely simple to extend the GlassFish v3 Prelude Administration Console. In fact, most of the functionality that ships in the console uses this approach, demonstrating the power of the mechanism quite nicely. The modularity of the GlassFish v3 kernel provides system integrators a practically unbounded array of opportunities for extending the application server, and the administration console's plugin service makes it extremely easy to add administration support for any extension you might create. How will you extend GlassFish?

(Cross-posted at steeplesoft.com)

Comments:

Thanks Jason!

This GFv3prelude is interesting, but a lot to digest, especially since it's on the side for me these days. (current projects are all non-glassfish and won't be changing anytime soon)

Is it just me, or did your first example lose its @Service annotation?

Regards,

-james.

Posted by James Stansell on November 07, 2008 at 05:48 AM CST #

Thanks, James. No, it's not just you. I fixed that. Must have been a copy and paste error. I \*think\* it's correct on steeplesoft.com, but I'll check there too. This theme also makes that table hard to read. I'll have to tinker with that. :)

Posted by Jason Lee on November 07, 2008 at 05:55 AM CST #

Post a Comment:
Comments are closed for this entry.
About

Jason Lee

Search

Categories
Archives
« April 2014
SunMonTueWedThuFriSat
  
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
   
       
Today