Section 2.1. A Community of Plug-ins - Eclipse Rich Client Platform: Designing, Coding, and Packaging Java Applications

2.1. A Community of Plug-ins

In Chapter 1, "Eclipse as a Rich Client Platform," we described the essence of Eclipse as its role as a component framework. The basic unit of function in this framework is called a plug-inthe unit of modularity in Eclipse. Everything in Eclipse is a plug-in. An RCP application is a collection of plug-ins and a Runtime on which they run. An RCP developer assembles a collection of plug-ins from the Eclipse base and elsewhere and adds in the plug-ins she has written. These new plug-ins include an application and a product definition along with their domain logic. In addition to understanding how Eclipse manages plug-ins, it is important to know which existing plug-ins to use and how to use them, and which plug-ins to build yourself and how to build them.

Small sets of plug-ins are easy to manage and talk about. As the pool of plug-ins in your application grows, however, grouping abstractions are needed to help hide some of the detail. The Eclipse teams define a few coarse sets of plug-ins, as shown in Figure 2-1.

Figure 2-1. 10,000-foot system architecture view

At the bottom of the figure is the Eclipse RCP as a small set of plug-ins on top of a Java Runtime Environment (JRE). The RCP on its own is much like a basic OS or the Java JRE itselfit is waiting for applications to be added.

Note

Don't take the boxes in Figure 2-1 too seriously. They are a guess, by the producers of the plug-ins, at groupings that are coherent to consumers of the plug-ins. The groupings are useful abstractions; but remember, for every person that wants some plug-in inside a box, there is someone who wants it outside. That's OK. You can build your own abstractions.

Fanning upwards in the figure is a collection of RCP applicationssome written by you, some by others, and some by Eclipse teams. The Eclipse IDE Platform, the traditional Eclipse used as a development environment, is itself just a highly functional RCP application. As shown in Figure 2-1, the IDE Platform requires some of the plug-ins in the Eclipse RCP. Plugged into the IDE Platform is the Eclipse Software Development Kit (SDK) with its Java and plug-in tooling and hundreds of other tools written by companies and the open source community.

This pattern continues. The general shape of the Eclipse RCP and your products is the samethey are both just sets of plug-ins that make up a coherent whole. These themes of consistency and uniformity recur throughout Eclipse.

Note

Notice in Figure 2-1 that the Eclipse RCP requires only Foundation Java class libraries. Foundation is a J2ME standard class set typically meant for embedded or smaller environments. See http://java.sun.com/products/foundation for more details. If you are careful to use only a Foundation-supported API, then you can ship Eclipse-based applications on a Java Runtime that is only about 6MB rather than the 40MB J2SE 1.4 JRE.

The internal detail for the Eclipse RCP plug-in set is shown in Figure 2-2. These plug-ins form the base of your RCP applications. Here we see a set of interdependent plug-ins that provide various capabilities as noted in the callout boxes. We could have zoomed in on any of the plug-in sets in Figure 2-1 and seen the same basic structurean example of uniformity. You are in fact free to slice and dice the RCP itself or any other plug-in set to suit your needs as long as the relevant plug-in interdependencies are satisfied. In this book, we focus on RCP applications as applications that use the full RCP plug-in set.

Figure 2-2. 1,000-foot RCP view

Managing the dependencies is a large part of building an Eclipse application. Plug-ins are self-describing and explicitly list the other plug-ins or functions that must be present for them to operate. The Runtime's job is to resolve these dependencies and knit the plug-ins together. It's interesting to note that these interdependencies are not there because of Eclipse, but because they are implicit in the code and structure of the plug-ins. Eclipse allows you to make the dependencies explicit and thus manage them effectively.