I would like to create a word document using a template, replace some variables (fields) and save it as a new word document.
I was thinking using Apache POI, http:/
You should look into the Aspose.Words components. They have recently begun providing a Java version of the component.
See the following link: Aspose.Word for Java
This supports Word automation, creation and advanced features such as mail merging without the need for an instance of Microsoft Word on the machine. The real benefits are that you are able to work within the context of an actual word document and not having to compromise by creating RTFs etc.
The Java version is not currently as fully featured as the .Net version but the main core functionality is there and they are pushing very hard to have a feature equivalent version soon.
Also, if you purchase the Java version you get a years free upgrades / support as the new releases are created.
If you use a template, and do not want to create the word document from scratch, for what I know, POI is a pretty good solution. You open the template and select the zones you want to replace.
They say POI is still is developpement, but I've been using it in production environnement and it works pretty good at the moment.