Metamodel classes for OpenJPA with Maven, Eclipse and m2e

Metamodel classes are a not-so-well known feature of the JPA 2.0 standard. They allow you to write typesafe criteria queries using metamodel attributes instead of plain old strings to reference entity fields. (See this tutorial for some more background.)

Metamodel classes are generated by an annotation processor during the build process, but this is not enabled by default. OpenJPA logs a runtime warning when you build a criteria query and the metamodel classes cannot be found. So even if you don't use the metamodel, you may want to generate it just to get rid of this warning.

This article explains how to generate the metamodel both in Maven batch builds and in the Eclipse workspace.

Multi-Instance Deployment from Eclipse to Tomcat

Problem

• You are developing a web application for Tomcat in Eclipse.
• You want to deploy multiple instances of the same application with different configurations directly from your workspace.
• Of course, you don't want to duplicate any projects in your workspace.

Solution

This scenario can be solved quite easily with the vanilla Apache Tomcat adapter of Eclipse WTP. There is no need for any additional Eclipse plugins.