Write a Java / PHP program to convert a KML file to a GeoJSON File

I have two kml files one with polygons and one with points that are updated each day. I need a php / java script that I can run on the webserver using cron to read the kml file at a set time each day and convert it to a GeoJSON file Input file name and output file name will be the same each day so it will need to overwrite the old file automatically. The kml file sizes are around 8MB Simplest option would be to convert the whole file but we only need the polygons and a few of the shape file fields in the GeoJSON file so if the conversion could also only extract the fields that we needed (normally 3 fields out of the 20 odd in the KML file) then that would be good as it would make the GeoJSOn file much smaller. I have seen python kmltogeojson converters on stack overflow so this should be pretty easy for a good programmer. Sample kml files can be provided Need work completed in two weeks.