在Eclipse中运行WordCount示例时的ClassNotFoundException

Question

我正在尝试运行WordCount Map/Reduce作业的示例代码。我正在Hadoop1.2.1上运行它。我用我的日食来运行它。下面是我尝试运行的代码：

package mypackage;

import java.io.IOException;
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.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
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.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;


public class WordCount {

    public static class Map extends
            Mapper<LongWritable, Text, Text, IntWritable> {
        private final static IntWritable one = new IntWritable(1);
        private Text word = new Text();

        public void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            String line = value.toString();
            StringTokenizer tokenizer = new StringTokenizer(line);
            while (tokenizer.hasMoreTokens()) {
                word.set(tokenizer.nextToken());
                context.write(word, one);
            }
        }
    }

    public static class Reduce extends
            Reducer<Text, IntWritable, Text, IntWritable> {

        public void reduce(Text key, Iterable<IntWritable> values,
                Context context) throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            context.write(key, new IntWritable(sum));
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        conf.set("mapred.job.tracker", "maprfs://,y_address");
        conf.set("fs.default.name", "hdfs://my_address");

        Job job = new Job(conf, "wordcount");
        job.setJarByClass(WordCount.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        job.setMapperClass(Map.class);
    job.setReducerClass(Reduce.class);

        job.setInputFormatClass(TextInputFormat.class);
        job.setOutputFormatClass(TextOutputFormat.class);

        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        job.waitForCompletion(true);    
    }   
}

13/11/04 13:27:53 INFO Mapred.JobClient：任务Id:Attitt_201310311611_0005_M_000000_0，状态：失败java.lang.RuntimeException：java.lang.ClassNotFoundException：com.rf.hadoopspikes.wordcount$map（位于org.apache.hadoop.conf.Configuration.getClass（配置.java:857)（位于org.apache.hadoop.mapreduce.jobcontext.getMapperClass（配置.java:857)（位于

我知道WordClass找不到，但我不知道如何使它工作。有什么想法吗？

Answer 1

当直接从Eclipse运行时，您需要确保类已经绑定到一个Jar文件中（然后hadoop将其复制到HDFS）。您的错误很可能与Jar尚未构建有关，或者在运行时，类是从输出目录运行的，而不是从绑定的Jar运行的。

尝试将类导出到一个jar文件中，然后从该jar文件运行WordCount类。您还可以使用Eclipse Hadoop插件，我认为它可以处理所有这些。最后一个选择是捆绑jar，然后从命令行启动（如各种Hadoop教程所述）