排序

public class IntKeyAscComparator extends WritableComparator {protected IntKeyAscComparator() {super(IntWritable.class, true);}@Overridepublic int compare(WritableComparable a, WritableComparable b) {return -super.compare(a, b);}}// key按照降序排列job.setSortComparatorClass(IntKeyAscComparator.class);