无法执行基本的Hadoop Mapreduce Wordcount示例

Question

javac -classpath /usr/local/hadoop/share/hadoop/common/hadoop-common-2.7.3.jar -d wordcount_classes WordCount.java

我使用本教程设置了hadoop。我还在stackoverflow：question上查阅了这个信息，并在/usr/local/hadoop中执行了bin/hadoop classpath命令。这是我得到的输出：

/usr/local/hadoop/etc/hadoop:/usr/local/hadoop/share/hadoop/common/lib/*:/usr/local/hadoop/share/hadoop/common/*:/usr/local/hadoop/share/hadoop/hdfs:/usr/local/hadoop/share/hadoop/hdfs/lib/*:/usr/local/hadoop/share/hadoop/hdfs/*:/usr/local/hadoop/share/hadoop/yarn/lib/*:/usr/local/hadoop/

但我不知道该怎么做，也不知道我下一步该怎么做！请救命！

Answer 1

您正在尝试使用许多hadoop依赖项JAR（hadoop-common-x.x.x.jar）之一编译源代码。包含错误消息中提到的映射包的jar是hadoop-mapreduce-client-core jar。

我建议您使用构建工具（如Maven或Gradle）构建源代码，因为它将为您管理可传递依赖项。

或者继续手动调用javac，尝试如下所示（未经测试）：

javac -cp '/usr/local/hadoop/share/hadoop/common/*' \
  -cp '/usr/local/hadoop/share/hadoop/hdfs/lib/*' \
  -cp '/usr/local/hadoop/share/hadoop/hdfs/*' \
  -cp '/usr/local/hadoop/share/hadoop/yarn/lib/*' \
  -cp '/usr/local/hadoop/share/hadoop/yarn/*' \
  -cp '/usr/local/hadoop/share/hadoop/mapreduce/lib/*' \ 
  -cp '/usr/local/hadoop/share/hadoop/mapreduce/*' \
  -d wordcount_classes WordCount.java