Question

我刚刚开始学习hadoop 1.1.2。

当我开始运行WordCount案例时，两种代码都很好。

命令A：

hadoop jar /usr/local/hadoop/hadoop-examples-1.1.2.jar WordCount input output

命令B：

hadoop jar /usr/local/hadoop/hadoop-examples-1.1.2.jar wordcount input output

唯一的区别是主要类名wordcount。

所以我的问题是天气主要类名wordcount是否不区分大小写？

更新：

@Amar说WordCount不能正常工作，我已经检查过他是对的。我被文件here误导了。官方文件需要更新。

但我仍然不知道为什么它必须是wordcount。

Answer 1

尝试在没有wordcount的情况下投放，例如： hadoop jar /usr/local/hadoop/hadoop-examples-1.1.2.jar input output

您将收到以下内容：

Unknown program 'input' chosen.
Valid program names are:
  aggregatewordcount: An Aggregate based map/reduce program that counts the words in the input files.
  aggregatewordhist: An Aggregate based map/reduce program that computes the histogram of the words in the input files.
  dbcount: An example job that count the pageview counts from a database.
  grep: A map/reduce program that counts the matches of a regex in the input.
  join: A job that effects a join over sorted, equally partitioned datasets
  multifilewc: A job that counts words from several files.
  pentomino: A map/reduce tile laying program to find solutions to pentomino problems.
  pi: A map/reduce program that estimates Pi using monte-carlo method.
  randomtextwriter: A map/reduce program that writes 10GB of random textual data per node.
  randomwriter: A map/reduce program that writes 10GB of random data per node.
  secondarysort: An example defining a secondary sort to the reduce.
  sleep: A job that sleeps at each map and reduce task.
  sort: A map/reduce program that sorts the data written by the random writer.
  sudoku: A sudoku solver.
  teragen: Generate data for the terasort
  terasort: Run the terasort
  teravalidate: Checking results of terasort
  wordcount: A map/reduce program that counts the words in the input files.

所以基本上第一个参数不是主类名，而是你要运行的示例程序名。

所以，它甚至不应该接受WordCount，它不适合我。以下命令与上面显示的结果相同：

bin/hadoop jar hadoop-examples-1.0.4.jar WordCount LICENSE.txt output

供您参考：主要类已在jar中包含的META-INF/MANIFEST.MF文件中定义： Main-Class: org/apache/hadoop/examples/ExampleDriver

Answer 2

它肯定区分大小写，因为它试图从jar中加载类WordCount或wordcount，具体取决于外壳。由于Java在这方面是区分大小写的，hadoop jar也是如此。

hadoop jar命令类名是否区分大小写？

2 个答案: