Rich Client Tutorial Part 2

The Rich Client Platform (RCP) allows you to build Java applications that can compete with native applications on any platform. Part 1 of the tutorial introduced you to the platform and the steps used to build the smallest possible RCP program. In part 2 we'll look at what we did in more detail and introduce some of the configuration classes that let you take control of much of the layout and functionality of an RCP application. This part has been updated for Eclipse 3.1.2

By Ed Burnette, SAS
August 9, 2004
Updated for 3.1.2: February 6, 2006

Introduction

In early versions of Eclipse, many functions of the IDE were hard-wired into the code. These included the name and location of the File menu, the title of the Workbench Window, and the existence of the status bar. This was fine for the IDE but when people started to use Eclipse as a basis for non-IDE programs, sometimes these things didn't make sense. Although all the source code was provided, it was inconvenient to find the right places that had to be changed.

So, beginning in Eclipse 3.0, the designers refactored the API to make these and other hard-wired aspects of the user interface controllable through public API. Subsequent releases have fine tuned that API and provided tooling in the Plug-in Development Environment (PDE) to lower the barriers to getting started using it. However, you'll eventually need to look behind the PDE wizards and editors to really understand what is going on.

In this part we'll examine the code and configuration files created in Part 1 of the tutorial. To keep the parts separate I've recreated the examples for each part under a different name. All the sample code for Part 2 may be found in the part2.zip archive file.

If you're following along with this tutorial in Eclipse and you're thinking of just renaming your old project, I don't recommend it. In Eclipse 3.1, Refactor > Rename does not work well on plug-in projects due to all the internal references in XML files and strings that don't participate. Hopefully this will be fixed in a future release.

Before we go any further let's clear up some possible confusion about the relationship between Applications, Workbenches, and Workbench Windows.

Applications, Workbenches, and Workbench Windows

The Application is a class you create that acts as your RCP program's main routine. You can think of it as the controller for the program. Just like the controller in a Model2 architecture, it is short and sweet and doesn't change significantly for different projects. All it does is create a Workbench and attach another class called a Workbench Advisor to it (Workbench Advisors will be covered more later).

The Workbench is declared and maintained for you as part of the RCP framework. There is only one Workbench but it can have more than one visible top-level Workbench Window. For example, in the Eclipse IDE, when you first start Eclipse you will see one Workbench Window, but if you select Window > New Window a second window pops up -- two Workbench Windows, but only one Workbench.

Ok, now that that's out of the way, let's see what those PDE wizards did for us, starting with the plug-in manifest.

Plug-in manifest

The plug-in manifest ties all the code and resources together. When you first create a plug-in, Eclipse will create and open the manifest for you automatically. The manifest is split into two files: MANIFEST.MF and plugin.xml. PDE provides a fancy editor to modify the options stored in these files (see Figure 1) but also allows you to edit the source directly.

Figure 1. The plug-in manifest editor provides a single interface for editing the manifest and related files. The tabs along the bottom of the editor access all the different sections in the GUI or the raw text files.

MANIFEST.MF

The OSGi bundle manifest is stored in MANIFEST.MF. OSGi is the name of a standard that Eclipse uses for dynamically loading plug-ins (see refererences). Listing 1 shows the OSGi bundle manifest generated by the plug-in wizard. Everything in this file can be edited by the Manifest editor, so there should be no need to edit it by hand. However if you need to, just double-click it in the Package Explorer to bring up the Manifest editor, then click on the MANIFEST.MF tab in the editor to see and modify the source.

For backwards compatability with Eclipse 2.1, Eclipse will recognize and load plug-ins that do not use MANIFEST.MF. However, this incurs a small performance penalty and is not recommended for plug-ins targeting Eclipse 3.0 and later.

Listing 1. MANIFEST.MF

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Part2 Plug-in
Bundle-SymbolicName: org.eclipse.ui.tutorials.rcp.part2; singleton:=true
Bundle-Version: 1.0.0
Bundle-Activator: org.eclipse.ui.tutorials.rcp.part2.Part2Plugin
Bundle-Localization: plugin
Require-Bundle: org.eclipse.ui,
 org.eclipse.core.runtime
Eclipse-AutoStart: true

plugin.xml

The Eclipse extension manifest is called plugin.xml. It's used for defining and using Eclipse extension points, so if you're not using extension points then this file may be omitted. Extension points are the fundamental way that Eclipse plug-ins are tied together so if you're not familiar with them see one of the articles in the Reference section. Listing 2 shows the plugin.xml file created by the PDE wizard.

Listing 2. plugin.xml

<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.0"?>
<plugin>

   <extension
         id="application"
         point="org.eclipse.core.runtime.applications">
      <application>
         <run
               class="org.eclipse.ui.tutorials.rcp.part2.Application">
         </run>
      </application>
   </extension>
   <extension
         point="org.eclipse.ui.perspectives">
      <perspective
            name="Part2 Perspective"
            class="org.eclipse.ui.tutorials.rcp.part2.Perspective"
            id="org.eclipse.ui.tutorials.rcp.part2.perspective">
      </perspective>
   </extension>
   <extension
         id="product"
         point="org.eclipse.core.runtime.products">
      <product
            application="org.eclipse.ui.tutorials.rcp.part2.application"
            name="RCP Tutorial 2"/>
   </extension>

</plugin>

The class name of the main program is defined with the org.eclipse.core.runtime.applications extension.

Although it's not an absolute requirement, I recommend keeping your id's and your class names the same except possibly for case. For historical reasons, Eclipse prepends the plug-in's id to the id of your top level plug-in elements (like extension). For example, even though the plugin.xml in listing 2 says id="application", the fully qualified id for that extension is org.eclipse.ui.tutorials.rcp.part2.application. Since the perspective's id is written on a sub-element (perspective) it has to be spelled out completely in the manifest (org.eclipse.ui.tutorials.rcp.part2.perspective). By convention only, package names and ids are lower case and class names are Pascal Case.

The main program

The org.eclipse.core.runtime.applications extension tells the Eclipse runtime the name of your main program. This is a class that implements IPlatformRunnable and a run() method. Listing 3 shows the simple implementation supplied by the plug-in wizard.

Listing 3. Application.java

The default perspective

A Perspective is a set of visible views, editors, and menus including their positions and sizes. In an RCP program you must define at least one perspective and make it the default. Perspectives are created by implementing IPerspectiveFactory using the class name referred to by the org.eclipse.ui.perspectives extension. See Listing 4 for the implementation provided by the plug-in wizard. The important part of this interface is the createInitialLayout() method where you position and open any views and/or editors you'd like the user to start with. So far in this example we haven't created any views so it's a pretty boring perspective.

Listing 4. Perspective.java

The Advisor classes

The main program referenced a class called ApplicationWorkbenchAdvisor. This is one of three Advisor classes that you use to configure all aspects of the Workbench such as the title, menu bars, and so on. These are the most important classes for an RCP developer to understand. You extend the base version of the class, for example WorkbenchAdvisor, in your RCP application and override one or more of the methods to set whatever options you want. Let's examine these classes now in more detail.

Workbench Advisor

Methods in this class are called from the platform to notify you at every point in the lifecycle of the Workbench. They also provide a way to handle exceptions in the event loop, and provide important parameters to the Workbench such as the default perspective. With the exception of createWorkbenchWindowAdvisor() and getInitialWindowPerspectiveId(), the methods on WorkbenchAdvisor do not have to be overridden. Listing 5 shows the implementation that was provided by the plug-in wizard.

Listing 5. ApplicationWorkbenchAdvisor.java

Why not an interface? You'll notice that WorkbenchAdvisor is an abstract class. For the most part, Eclipse APIs shun abstract classes in favor of interfaces and base classes that implement those interfaces. In this case, the designers intend for WorkbenchAdvisor to always be implemented by the RCP application, and the base class doesn't contain any significant functionality. Also it is very likely that new methods will need to be added to the base class in the future (something that is difficult using interfaces). So this was a deliberate design choice. See the article on evolving Java APIs in the reference section for more tips.

Workbench lifecycle hooks

The Workbench Advisor class has several methods that are called at defined points in the Workbench's lifecycle (see Table 1). By overriding these you can run whatever code you want at these points.

Table 1. Workbench lifecycle hooks provided by WorkbenchAdvisor.

Event loop hooks

The event loop is the code that is running most of the time during the life of the Workbench. It handles all user inputs and dispatches them to the right listeners. RCP provides a couple of hooks to handle crashes and perform work during idle time (see Table 2). Note however that the Jobs interface (see References) is a better way of performing long running work than this idle hook.

Table 2. Event loop hooks provided by WorkbenchAdvisor.

Information getting hooks

Next, there are few methods you can implement that the platform will call to get information about your application (see Table 3). The most important one (and the only one that is not optional) is getInitialWindowPerspectiveId. We used this in Listing 5 to return the id of the starting perspective.

Table 3. Information request methods you can override in WorkbenchAdvisor.

Advanced configuration

The WorkbenchAdvisor events above should be sufficient for most applications, but just in case, RCP provides another method to take complete control of how your application windows and controls are created. It's listed in Table 4 for completeness but I don't expect many programs will need it.

Table 4. Advanced methods in org.eclipse.ui.application.WorkbenchAdvisor.

Workbench Window Advisor

This class is used to control the status line, toolbar, title, window size, and other things you'll almost certainly want to customize. You can also use it to hook into all the various lifecycle events of the Workbench Windows. Listing 6 shows the implementation provided by the plug-in wizard.

Listing 6. ApplicationWorkbenchWindowAdvisor.java

Methods on WorkbenchWindowAdvisor (see Table 5 and Table 6) will all need access to a Configurer interface (in this case, IWorkbenchWindowConfigurer) in order to do anything so they're expected to call getWindowConfigurer() to fetch it. You call methods on the Configurer interfaces to actually change the options. These interfaces are not covered in any detail in this tutorial but you can refer to their Javadoc for more information.

Table 5. Workbench window lifecycle hooks provided by WorkbenchWindowAdvisor.

Table 6. Advanced methods in WorkbenchWindowAdvisor.

ActionBar Advisor

In Eclipse jargon, "action bar" is a catch-all term for menus, toolbars, and status bars. The ActionBar Advisor handles creating Actions within these locations. A plug-in can also contribute actions dynamically with its plugin.xml file. See Listing 7 for the implementation provided by the plug-in wizard and Table 7 for the methods.

The whole action, command and keybinding system is a bit of a mess in Eclipse 3.1. For example you can't add combo boxes to action bars, and plugin.xml can't contribute actions to the status bar. Getting key bindings to work involves multiple steps. Hopefully this will be cleaned up in a future release.

Listing 7. ApplicationActionBarAdvisor.java

Table 7. Methods you can override in ActionBarAdvisor.

Plug-in class

The plug-in class is an optional singleton class that can be used to store global information for the plug-in. It's also a convenient place to put a few static utility functions used by other classes in the plug-in. See Listing 8 for the plug-in class that was created for us by the plug-in wizard.

Listing 8. Part2Plugin.java

Build properties

The build.properties file (see Listing 9) will be needed when exporting the application for others to use. In particular if your application needs any resources like icons they should be listed here in the bin.includes section. The Plug-in Manifest editor provides a convenient interface to modify this file that is less error-prone than modifying it by hand.

Listing 9. build.properties

source.. = src/
output.. = bin/
bin.includes = plugin.xml,\
               META-INF/,\
               .

Conclusion

In part 2 of this tutorial, we looked at some of the API of the Rich Client Platform that allows you to develop customized native-looking client-side Java programs. The next part will delve into branding and deploying your application so others can use it. All the sample code for this part is included in the part2.zip archive file that accompanies this document.

References

RCP Tutorial Part 1
RCP Tutorial Part 3
Eclipse Rich Client Platform
The Equinox project (OSGi in Eclipse)
How to Internationalize your Eclipse Plug-in
PDE Does Plug-ins
Notes on the Eclipse Plug-in Architecture
On the Job: The Eclipse Jobs API
Almost All Java Web Apps Need Model 2 (introduction to the Model 2 architecture)
Evolving Java-based APIs

To discuss or report problems in this article see bug 104170.

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