Hadoop问题：编译WordCount程序报错：class file for org.apache.commons.cli.Options not found
第一次编译Hadoop的程序，将安装程序自带的WordCount程序拿出来编译执行，编译时遇到如下错误：

ubuntu@ubuntu:~/dev/wordcount$ javac -classpath /home/ubuntu/hadoop-1.0.4/hadoop-core-1.0.4.jar -d bin WordCount.java
WordCount.java:53: cannot access org.apache.commons.cli.Options
class file for org.apache.commons.cli.Options not found
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
                         ^
1 error

在网上搜索了一下，找到了原因，在 classpath 中再加上一个 jar 包即可：

ubuntu@ubuntu:~/dev/wordcount$ javac -classpath /home/ubuntu/hadoop-1.0.4/hadoop-core-1.0.4.jar:/home/ubuntu/hadoop-1.0.4/lib/commons-cli-1.2.jar -d bin WordCount.java
ubuntu@ubuntu:~/dev/wordcount$ ls bin/*.class
bin/WordCount.class  bin/WordCount$IntSumReducer.class  bin/WordCount$TokenizerMapper.class