Eclipse is an IDE (Integrated Development Environment) with editors, debuggers, and panels to view type hierarchies and show all uses of particular classes and variables. It is an excellent tool to edit and devleop software, including J2EE applications. However, when you finally have your program running, it provides no good support to package your code for production deployment or general distribution. When you work with Eclipse, all you really see is the source. When you edit and save a source file, Eclipse compiles the code and "pushes" this source change even to the point of hot deploying the change into a running Application Server.
Maven is a batch tool for building and packaging production artifacts. An artifact may be the WAR file for a Web application, or the EAR file for a J2EE application (containing WARS and EJBs), or it may just be a component library packaged as a JAR file. In order to create the artifact, Maven will compile any source, copy data files, and even download over the internet any referenced public Java JAR libraries. Maven "pulls" all these pieces together to create the production deploy file. However, it has no editors or debuggers to do development.
These two tools handle entirely different ends of the software development process. Each concentrates its energy doing a specific function that the other tools ignores entirely. Together, they provide fairly good coverage of the entire software development cycle.
Maven and Eclipse were developed separately to do different things according to different strategies. Where Maven has specific demands, Eclipse is completely flexible and can adapt to them. Where Eclipse has specific demands, Maven is flexible and can adapt. For them to work together optimally, you just have to create a hybrid environment that reconciles the two distinct philosophies
This document began as a set of instructions for developing the Central Authentication Server application (CAS) using Maven and Eclipse. Several releases of CAS, Maven, and Eclipse later it is clear that any static instructions will not solve the problem. However, to do better it is necessary to explain a bit about how Maven and Eclipse work and just what you can expect from the combination. CAS will remain the example used when explaining configurations and options, but this information may be useful to people doing other types of software configuration.
This cannot be a serious introduction to either Maven as a comprehensive project building utility or Eclipse as an IDE. There are books that cover the intricate details of each. However, it will cover a bit more than the two page tutorial that you find with either system. Move though the material sequentially and skip pages that cover material with which you are already familiar, although the objective here will be to provide more explanation than you normally get about how things work. By design, each major topic has its own URL that you can bookmark or link to.