Hadoop Hello World

Hadoop单机环境配置OK后，需要找个例子测试一下Mapreduce功能。因此从Hadoop源代码中找到一个例子:WordCount.java，来验证。

编译过程如下：

cd hadoop-example/
javac -classpath ../hadoop-2.1.0-beta/share/hadoop/common/hadoop-common-2.1.0-beta.jar:../hadoop-2.1.0-beta/share/hadoop/common/lib/commons-cli-1.2.jar:../hadoop-2.1.0-beta/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.1.0-beta.jar:../hadoop-2.1.0-beta/share/hadoop/mapreduce/hadoop-mapreduce-client-jobclient-2.1.0-beta.jar -d WordCount WordCount.java
cd WordCount
jar -cfe WordCount.jar org.apache.hadoop.examples.WordCount org/*
hadoop fs -put helloworld.txt
hadoop jar WordCount.jar /user/root/helloworld.txt ./result

hadoop-example和hadoop-2.1.0-beta在同一级目录。

helloworld.txt的内容为：

Hello

World

nihao

wohao

Hello

Hello

World

计算结果：

Hello   3

World   2

nihao   1

wohao   1

Hadoop版本：Hadoop 2.1.0-beta

配置过程可参考博客中前几篇文章