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 debug software, including J2EE applications. With Eclipse you can check out the current version of source from Subversion, make changes to the code, test the changes, and check the modifications back into Subversion.
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.
Eclipse is not good at building artifacts, and Maven has no editors or debuggers. However, if you combine the two, then you have full coverage for the entire application development cycle.
However, since the two tools were developed independently of each other, they have different strategies and conventions. There is an area of overlap that fortunately covers almost all the function needed for our application development, but it is important to understand the boundaries. Maven has a particular directory structure while Eclipse can handle any directory tree, so you use the Maven convention to layout the project. Use the Maven POM to describe the project and let Eclipse read that file and automatically configure its view of the project. However, it will not be long before you configure at least one Maven option that Eclipse does not understand to do something Eclipse cannot exactly duplicate. Since Maven is going to build the code that actually runs in production, you need to also use Maven to build exactly the same code in development, but once you use any option that Eclipse cannot understand or duplicate, you have to bypass the Eclipse automatic compile-and-debug cycle and create a new hybrid Eclipse-Maven-Debug process that you run manually.
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.