Question

为什么简单的Hadoop map / reduce教程会为我标记错误。这是直接从Apache教程中复制的代码：

public class Mining {

public static class MapClass extends MapReduceBase implements 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, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
        String line = value.toString();
        StringTokenizer tokenizer = new StringTokenizer(line);
        while (tokenizer.hasMoreTokens()) {
            word.set(tokenizer.nextToken());
            output.collect(word, one);
        }
    }
}

public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
    public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
        int sum = 0;
        while (values.hasNext()) {
            sum += values.next().get();
        }
        output.collect(key, new IntWritable(sum));
    }
}

public static void main(String[] args) throws Exception {
    JobConf conf = new JobConf(Mining.class);
    conf.setJobName("wordcount");

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

    conf.setMapperClass(MapClass.class);
    conf.setCombinerClass(Reduce.class);
    conf.setReducerClass(Reduce.class);

    conf.setInputFormat(TextInputFormat.class);
    conf.setOutputFormat(TextOutputFormat.class);

    FileInputFormat.setInputPaths(conf, new Path(args[0]));
    FileOutputFormat.setOutputPath(conf, new Path(args[1]));

    JobClient.runJob(conf);
}
}

错误发生在编译时，是：

The type Mapper is not generic; it cannot be parameterized with arguments <LongWritable, Text, Text, IntWritable>

我在别处读过这可能是因为你的项目中使用了过时的Hadoop jar文件。我正在使用最新的稳定jar，hadoop-core-1.2，我也试过0.20。关于问题是什么的任何建议？

编辑 - 导入列表：

import java.io.IOException;
import java.util.*;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*; 
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.*;

Answer 1

请检查一次导入。也许您已经在程序中混合了旧API和新API。另外，我建议您使用新的API，即 mapreduce ，而不是 mapred 。

HTH

运行简单的Hadoop map / reduce教程

1 个答案: