(Update 2009.05.16: add JAVA_JVM_VERSION setting)
To build Nutch 1.0, you need JDK 1.6. Unless you’ll got
[javac] class file has wrong version 50.0, should be 49.0 error message.
For a system that has more than one version of JDK installed.
It is possible to change to a desired version only at the time you need it (look for
j16 script in this thread). I found myself more convenient with just changed the default version.