Hadoop 学习笔记：java.lang.NoSuchMethodException: DataJoin$TaggedWritable.()

运行 Hadoop in Action 里面关于datajoin的例子时报这个错，解决方案是为TaggedWritable 类加一个无参构造方法。原因是Hadoop uses reflection to create this object, and requires a default constructor (no args).

详：

http://stackoverflow.com/questions/10201500/hadoop-reduce-side-join-using-datajoin