Including external jars in a Hadoop job

办法1：

把所有的第三方jar和自己的class打成一个大的jar包，这种方案显然笨拙，而且更新升级比较繁琐。 

办法2： 
在你的project里面建立一个lib文件夹，然后把所有的第三方jar包放到里面去，hadoop会自动加载lib依赖里面的jar。 

此方法来自Including external jars in a Hadoop job

"Luckily, I bumped into a solution suggested Doug Cutting as an answer to someone who had a similar predicament. The solution was to create a “lib” folder in your project and copy all the external jars into this folder. According to Doug, Hadoop will look for third-party jars in this folder. It works great! "