在CDH4上运行map reduce作业的示例

Question

我是CDH4和Hadoop新手。

我正在尝试运行wordcountexample并得到以下错误。你能纠正我，让我知道是什么问题吗?

WordCount.java:25: interface expected here
            public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
                                                                           ^
WordCount.java:39: interface expected here
            public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
                                                                               ^
WordCount.java:56: setMapperClass(java.lang.Class<? extends org.apache.hadoop.mapred.Mapper>) in org.apache.hadoop.mapred.JobConf cannot be applied to (java.lang.Class<WordCount.Map>)
              conf.setMapperClass(Map.class);
                  ^
WordCount.java:57: setCombinerClass(java.lang.Class<? extends org.apache.hadoop.mapred.Reducer>) in org.apache.hadoop.mapred.JobConf cannot be applied to (java.lang.Class<WordCount.Reduce>)
              conf.setCombinerClass(Reduce.class);
                  ^
WordCount.java:58: setReducerClass(java.lang.Class<? extends org.apache.hadoop.mapred.Reducer>) in org.apache.hadoop.mapred.JobConf cannot be applied to (java.lang.Class<WordCount.Reduce>)
              conf.setReducerClass(Reduce.class);
                  ^
WordCount.java:60: setInputFormat(java.lang.Class<? extends org.apache.hadoop.mapred.InputFormat>) in org.apache.hadoop.mapred.JobConf cannot be applied to (java.lang.Class<org.apache.hadoop.mapreduce.lib.input.TextInputFormat>)
              conf.setInputFormat(TextInputFormat.class);
                  ^
WordCount.java:63: cannot find symbol
symbol  : method setInputPaths(org.apache.hadoop.mapred.JobConf,org.apache.hadoop.fs.Path)
location: class org.apache.hadoop.mapreduce.lib.input.FileInputFormat
              FileInputFormat.setInputPaths(conf, new Path(args[0]));
                             ^
WordCount.java:64: setOutputPath(org.apache.hadoop.mapreduce.Job,org.apache.hadoop.fs.Path) in org.apache.hadoop.mapreduce.lib.output.FileOutputFormat cannot be applied to (org.apache.hadoop.mapred.JobConf,org.apache.hadoop.fs.Path)
              FileOutputFormat.setOutputPath(conf, new Path(args[1]));

编译命令:

javac -classpath /usr/lib/hadoop/*:/usr/lib/hadoop/client/* WordCount.java 

程序是wordcountexample

Answer 1

问题是-classpath选项。您需要给出jar的绝对路径。*是不够的。给出用:

Answer 2

对于CHD4请尝试:

$ javac -classpath 'hadoop classpath' WordCount.java