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我是hadoop的新手。我从网上得到了这段代码

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.*;

public class Gender {

   private static String genderCheck = "female";

   public static class Map extends MapReduceBase implements Mapper {
       private final static IntWritable one = new IntWritable(1);
       private Text locText = new Text();

       public void map(LongWritable key, Text value, OutputCollector output, Reporter reporter) throws IOException {
           String line = value.toString();
           String location = line.split(",")[14] + "," + line.split(",")[15];
           long male = 0L;
           long female = 0L;
           if (line.split(",")[17].matches("\d+") && line.split(",")[18].matches("\d+")) {
               male = Long.parseLong(line.split(",")[17]);
               female = Long.parseLong(line.split(",")[18]);
           }
           long diff = male - female;
           locText.set(location);
           if (Gender.genderCheck.toLowerCase().equals("female") && diff < 0) {
               output.collect(locText, new LongWritable(diff * -1L));
           }
           else if (Gender.genderCheck.toLowerCase().equals("male") && diff
> 0) {
               output.collect(locText, new LongWritable(diff));
           }
       }    }

   public static void main(String[] args) throws Exception {
       JobConf conf = new JobConf(Gender.class);
       conf.setJobName("gender");
       conf.setOutputKeyClass(Text.class);
       conf.setOutputValueClass(LongWritable.class);
       conf.setMapperClass(Map.class);

       if (args.length != 3) {
           System.out.println("Usage:");
           System.out.println("[male/female] /path/to/2kh/files /path/to/output");
           System.exit(1);
       }

       if (!args[0].equalsIgnoreCase("male") && !args[0].equalsIgnoreCase("female")) {
           System.out.println("first argument must be male or female");
           System.exit(1);
       }
       Gender.genderCheck = args[0];

       conf.setInputFormat(TextInputFormat.class);
       conf.setOutputFormat(TextOutputFormat.class);
       FileInputFormat.setInputPaths(conf, new Path(args[1]));
       FileOutputFormat.setOutputPath(conf, new Path(args[2]));
       JobClient.runJob(conf);    }

}

当我使用“javac -cp /usr/local/hadoop/hadoop-core-1.0.3.jar Gender.java”编译这段代码时

收到以下错误：

“Gender.Map 不是抽象的，并且不会覆盖 org. apache.hadoop.mapred.Mapper 公共静态类 Map 扩展 MapReduceBase 实现 Mapper"

我怎样才能正确编译它？

4

2 回答 2

1

更改类 Maper 类声明如下：

public static class Map extends MapReduceBase implements Mapper<LongWritable,Text,Text, LongWritable>

如果您不指定任何特定的类名，则需要具有如下的 map 函数：

@Override
public void map(Object arg0, Object arg1, OutputCollector arg2, Reporter arg3) throws IOException {
    // TODO Auto-generated method stub
}

现在，特定类型在这里表示预期的输入键值对类型和映射器的输出键值类型。

在您的情况下，输入键值对是LongWritable-Text.

而且，从您的方法调用猜测output.collect，您的映射器输出键值对是Text-LongWritable.

因此，您的 Map 类应实施Mapper<LongWritable,Text,Text, LongWritable>。

您的代码中还有一个错误 -

Using "\d+"will not compile as \dhas no meaning,在反斜杠之后它需要一个特殊的转义序列，所以我猜对你来说以下应该有效： line.split(",")[17].matches("\\d+")

于 2013-04-08T07:07:41.557 回答
0

更改地图类如下：

public static class Map extends MapReduceBase implements Mapper <Input key, Input value, Output Key , Output Value>

在您的情况下，输入键是LongWritable，输入值是Text，输出键是Text，输出值是LongWritable 

public static class Map extends MapReduceBase implements Mapper <LongWritable, Text, Text,LongWritable>
于 2017-09-12T07:22:49.513 回答