Nutch2 插件機制（用於二次開發）

http://www.open-open.com/doc/view/ac5b72b3366f4586960edc9db49e31b9

http://www.ibm.com/developerworks/cn/java/j-lo-nutchplugin/

http://blog.csdn.net/geogre_jsj/article/details/5726646