hadoop中mapreduce提交作业到集群运行报错ClassNotFoundException
错误信息:
解决方法:
在代码中添加:
job.setJarByClass(MyWordCount.class);
如果未指定,打印信息中会提示:
No job jar file set. User classes may not be found. See Job or Job#setJar(String).
这里贴上官方demo中WordCount类的反编译代码:
package org.apache.hadoop.examples;
import java.io.IOException;
import java.io.PrintStream;
import java.util.Iterator;
import java.util.StringTokenizer;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Mapper.Context;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.Reducer.Context;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
public class WordCount
{
public static void main(String[] args)
throws Exception
{
Configuration conf = new Configuration();
String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
if (otherArgs.length < 2) {
System.err.println("Usage: wordcount <in> [<in>...] <out>");
System.exit(2);
}
Job job = new Job(conf, "word count");
job.setJarByClass(WordCount.class);
job.setMapperClass(TokenizerMapper.class);
job.setCombinerClass(IntSumReducer.class);
job.setReducerClass(IntSumReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
for (int i = 0; i < otherArgs.length - 1; ++i)
FileInputFormat.addInputPath(job, new Path(otherArgs[i]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[(otherArgs.length - 1)]));
System.exit(1);
}
public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable>
{
private IntWritable result;
public IntSumReducer()
{
this.result = new IntWritable();
}
public void reduce(Text key, Iterable<IntWritable> values, Reducer<Text, IntWritable, Text, IntWritable>.Context context) throws IOException, InterruptedException
{
int sum = 0;
for (Iterator i$ = values.iterator(); i$.hasNext(); ) { IntWritable val = (IntWritable)i$.next();
sum += val.get();
}
this.result.set(sum);
context.write(key, this.result);
}
}
public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable>
{
private static final IntWritable one = new IntWritable(1);
private Text word;
public TokenizerMapper()
{
this.word = new Text();
}
public void map(Object key, Text value, Mapper<Object, Text, Text, IntWritable>.Context context) throws IOException, InterruptedException {
StringTokenizer itr = new StringTokenizer(value.toString());
while (itr.hasMoreTokens()) {
this.word.set(itr.nextToken());
context.write(this.word, one);
}
}
}
}