无法执行基本的Hadoop MapReduce Wordcount 示例

Question

我正在尝试运行WordCount示例。但是我在编译程序时遇到了一些问题。

我得到错误:

错误:package org.apache.hadoop.mapred不存在

执行后

:

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hadoop。我还在stackoverflow:问题上查找了这个问题，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/hdfs:/usr/local/hadoop/share/hadoop/hdfs/lib/*:/usr/local/hadoop/share/hadoop/hdfs/hdfs/*:/usr/local/hadoop/share/hadoop/yarn/lib/*:/usr/local/hadoop/share/hadoop/yarn/lib/*:/usr/local/hadoop/share/hadoop/mapreduce/lib/*:/usr/local/hadoop/share/hadoop/mapreduce/lib/*:/usr/local/hadoop/share/hadoop/mapreduce/lib/*:/usr/local/hadoop/share/hadoop/mapreduce/contrib/capacity-scheduler/*.jar

但我不知道该怎么做，也不知道下一步该怎么办!请帮助!

Answer 1

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

我建议你使用像Maven或Gradle这样的构建工具来构建你的源代码，因为它会为你管理可传递的依赖关系。

或者继续手动调用javac，请尝试这样做(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