I think that in order to generate a .jasper file I need a build.xml file, so that I cant use an ant task.
But in the Jasper Studio interface, there is no Export->General->ant option.
Do I need a Jasper Studio plugin for Eclipse in order for Eclipse to export a build.xml file?
Alternatively I could use a Java program to do it, but I can't find a generic java source.
in order to generate .jasper file you simply need to click on the related button for compilation on the top (inner) toolbar: the first button on the left. See attached screenshot. This way you can compile your report.
There is also the possibility to generate automatically the .jasper files for the JRXML reports you are creating. You can check the menu item that you can find under "Project > Build Automatically". This option will perform a complete compilation of all the reports (and also Java classes) that are in the projects of your workspace. The option has been disabled by default in the recent version, since it can be timewaster, especially when there are a lot of projects and reports.
Having it enabled, everytime you will save a report, the dedicated .jasper file will be generated.