MapReduce-tutorials is a project mainly written in Java, it's free.
From Hadoop Definitive Guide + online tutorials
Java-programs from Hadoop Definitive Guide and online Hadoop tutorials.
A note to self is:
mkdir weather_classes
javac -cp /Users/claus/devel/hadoop/hadoop-core-0.20.203.0.jar -d weather_classes MaxTemperatureMapper.java javac -cp /Users/claus/devel/hadoop/hadoop-core-0.20.203.0.jar -d weather_classes MaxTemperatureReducer.java javac -cp /Users/claus/devel/hadoop/hadoop-core-0.20.203.0.jar:weather_classes -d weather_classes MaxTemperature.java jar -cvf maxtemperature.jar -C weather_classes . hadoop jar maxtemperature.jar no.gnome.mapreduce.MaxTemperature input/temperature output