Hadoop 应用程序找不到 Reducer

Question

我正在尝试创建一个从 Hbase table 读取并将作业结果写入文本文件的 mapreduce 应用程序。我的驱动程序代码如下所示：

    Configuration conf = HBaseConfiguration.create();
    Job job = Job.getInstance (conf, "mr test");
    job.setJarByClass(Driverclass.class);
    job.setCombinerClass(reducername.class);
    job.setReducerClass(reducername.class);

    Scan scan = new Scan();
    scan.setCaching(500);            
    scan.setCacheBlocks(false);        

    String qualifier = "qualifname"; // comma seperated
    String family= "familyname";
    scan.addColumn(Bytes.toBytes(family), Bytes.toBytes(qualifier));

    TableMapReduceUtil.initTableMapperJob("tablename", 
                                           scan, 
                                           mappername.class, 
                                           Text.class, Text.class, 
                                           job);

调用 initTableMapperJob 时，我得到一个 ClassNotFoundException：class reducername not found。

class 在同一个包内的另一个 java 文件中定义。我使用几乎相同的配置来尝试通常的 wordcount 示例并且工作正常。然后我改变了映射器的类型和它的配置方式，我得到了这个错误。有人可以帮助我吗？

编辑：reducer class 的代码是：

package mr.roadlevelmr;
import java.io.IOException;
import java.util.ArrayList;
import java.util.StringTokenizer;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.Reducer;
public class reducername extends Reducer <Text, Text, Text, Text>{
    private Text result= new Text();

    public void reduce (Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException{
       ArrayList<String> means = new ArrayList<String>();
        for (Text val : values){
            means.add(String.valueOf(val.getBytes()));
        }
        result.set(newMean(means));
        context.write(key, result);
    }

Answer 1

您应该按如下方式使用 Map reduce 实用程序：

TableMapReduceUtil.initTableMapperJob("tablename", 
                                       scan, 
                                       mappername.class, 
                                       Text.class, Text.class, 
                                       job);Ok think I found the issue!

比添加减速器和组合器

job.setCombinerClass(reducername.class);
job.setReducerClass(reducername.class);
boolean b = job.waitForCompletion(true);

而不是将减速器添加到 table 映射器作业

Hadoop 应用程序找不到 Reducer

Hadoop application cannot find Reducer

java

hadoop

hbase

reducers