Android :: Generate Java Source Code In Eclipse?

Does anyone know what approach one can take to automatically generate Java source code, from for example an xml or json file, in eclipse? One great example of what I am thinking of doing is what Google Android sdk does: they have an R class generated automatically from the resources. Every time a resource file is saved in Eclipse R class is automatically regenerated.

UPDATE: Example:
In the text (xml or json file) I have the following:
<tags>
<tag id="ALPHA">
<description>The first alpha tag.</description>
<value>231232</value> </tag> <tag id="BETA">
<description>This is the beta tag.</description>
<value>231232</value> </tag>

Then in my generated java class, say R I would have something like:
R.tags.ids.ALPHA //refers to an enum value for example
R.tags.values.ALPHA //refers to final int with avlue 231232
R.tags.descriptions.ALPHA //refers to the String with description