job.setmapperclass报错

如果您在使用 Hadoop MapReduce 进行开发时，调用 `job.setMapperClass` 时出现错误，请检查以下几点：

1. 是否正确导入了 `org.apache.hadoop.mapreduce.Job` 类和 `org.apache.hadoop.mapreduce.Mapper` 类。

2. 是否正确继承了 Mapper 类，且实现了 `map` 函数。例如：

public static class MyMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        // TODO: 实现 map 函数
    }
}

3. 是否正确设置了 Mapper 类，例如：

Job job = new Job(conf, "myjob");
job.setMapperClass(MyMapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);

如果您已经检查了以上几点，仍然无法解决问题，请提供更多详细信息，我会尽力帮助您解决问题。

相关问题

Configuration conf = new Configuration(); Job job = Job.getInstance(conf, "word count"); job.setJarByClass(WordCountDriver.class); job.setMapperClass(WordCountMapper.class); job.setCombinerClass(WordCountReducer.class); job.setReducerClass(WordCountReducer.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); System.exit(job.waitForCompletion(true) ? 0 : 1);

这是一个使用Hadoop MapReduce框架实现的Word Count程序的驱动程序代码。其中`job.setMapperClass(WordCountMapper.class)`指定了Map阶段使用的Mapper类，`job.setReducerClass(WordCountReducer.class)`指定了Reduce阶段使用的Reducer类，`FileInputFormat.addInputPath(job, new Path(args[0]))`指定输入路径，`FileOutputFormat.setOutputPath(job, new Path(args[1]))`指定输出路径。程序最后调用`job.waitForCompletion(true)`提交作业并等待作业完成，`System.exit(job.waitForCompletion(true) ? 0 : 1)`表示当作业完成时退出程序并返回0，否则返回1。

package wc; import java.io.IOException; import org.apache.hadoop.mapreduce.Mapper; 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.Reducer; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.util.GenericOptionsParser; public class WordCountMain { public static void main(String[] args) throws Exception{ // TODO Auto-generated method stub Configuration conf = new Configuration(); conf.set("fs.default.name","hdfs://localhost:9000"); String[] otherArgs = new String[]{"input","output"}; /* 直接设置输入参数 */ if (otherArgs.length != 2) { System.err.println("Usage: wordcount <in><out>"); System.exit(2); } Job job = Job.getInstance(conf,"Merge and duplicate removal"); job.setJarByClass(WordCountMapper.class); job.setMapperClass(Map.class); job.setCombinerClass(WordCountReduce.class); job.setReducerClass(WordCountReduce.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(Text.class); FileInputFormat.addInputPath(job, new Path(otherArgs[0])); FileOutputFormat.setOutputPath(job, new Path(otherArgs[1])); System.exit(job.waitForCompletion(true) ? 0 : 1); } } package wc; import java.io.IOException; import org.apache.hadoop.mapreduce.Mapper; import org.apache.hadoop.io.Text; public class WordCountMapper{ public static class Map extends Mapper<Object, Text, Text, Text>{ private static Text text = new Text(); public void map(Object key, Text value, Context context) throws IOException,InterruptedException{ text = value; context.write(text, new Text("")); } } } job.setmapperclass出错

在您的代码中，您定义了一个名为 WordCountMapper 的类，该类实际上应该是一个 Mapper 类，并且应该继承 Mapper 接口。但是，在您的代码中，WordCountMapper 类没有继承 Mapper 接口，因此在设置 Mapper 类时出现了错误。

您需要将 WordCountMapper 类修改为一个 Mapper 类，并且让它继承 Mapper 接口，如下所示：

package wc;

import java.io.IOException;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.io.Text;

public class WordCountMapper extends Mapper<Object, Text, Text, Text> {

    private static Text text = new Text();

    public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
        text = value;
        context.write(text, new Text(""));
    }
}

然后，您需要将 `job.setMapperClass(Map.class)` 修改为 `job.setMapperClass(WordCountMapper.class)`，以设置正确的 Mapper 类。