Hadoop：没有这样的方法例外 [英] Hadoop: No Such Method Exception

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问题描述

我写了一个MapReduce程序，代码如下： 

  import java.io.IOException; 
 import java.util.Iterator; 
 import org.apache.hadoop.io.IntWritable; 
 import org.apache.hadoop.io.LongWritable; 
 import org.apache.hadoop.io.Text; 
 import org.apache.hadoop.mapreduce。*; 
导入org.apache.hadoop.fs.Path; 
导入org.apache.hadoop.conf。*; 
 import org.apache.hadoop.io。*; 
 import org.apache.hadoop.mapred.Reporter; 
 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; 
 $ b $ public class MaxTemperature {
 
 public class MaxTemperatureMapper扩展Mapper< LongWritable，Text，Text，IntWritable> {
 private static final int MISSING = 9999; 
 $ b $ public void map（LongWritable key，Text Value，Context context，Reporter reporter）throws IOException，InterruptedException {
 String line = Value.toString（）; 
 String year = line.substring（15,19）; 
 int airTemperature; 
 if（line.charAt（87）=='+'）
 airTemperature = Integer.parseInt（line.substring（88,92））; 
 else 
 airTemperature = Integer.parseInt（line.substring（87,91））; 
字符串质量= line.substring（92,93）; （airTemperature！= MISSING& amp; quality.matches（[01459]））
 context.write（new Text（year），new IntWritable（airTemperature））; 
 
 
 $ b $ public class MaxTemperatureReducer extends Reducer< Text，IntWritable，Text，IntWritable> {
 public void reduce（Text Key，Iterator< IntWritable> Values，上下文上下文，Reporter记者）抛出IOException，InterruptedException {
 
 int maxValue = Integer.MIN_VALUE; 
 while（Values.hasNext（））
 maxValue = Math.max（maxValue，Values.next（）。get（））; 
 context.write（Key，new IntWritable（maxValue））; 
 
 
 
 $ b public static void main（String [] args）throws Exception {
 if（args.length！= 2）{
 System.err.println（Usage：WeatherTemperature< input path>< output path>）; 
 System.exit（-1）; 
} 
配置conf = new Configuration（）; 
工作职位=新职位（conf，最高温度计算器）; 
 job.setJarByClass（MaxTemperature.class）; 
 
 job.setOutputKeyClass（Text.class）; 
 job.setOutputValueClass（IntWritable.class）; 
 
 job.setMapperClass（MaxTemperatureMapper.class）; 
 job.setReducerClass（MaxTemperatureReducer.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）; 
} 
}

我使用以下命令运行该程序的.jar命令： 

  hadoop jar weather.jar MaxTemperature输入输出
   
 
我收到以下错误消息： 13 00:52:05信息mapred.JobClient：任务ID：attempt_201206121354_0007_m_000000_0，状态：FAILED 
 java.lang.RuntimeException：java.lang.NoSuchMethodException：MaxTemperature $ MaxTemperatureMapper。< init>（）
 at org.apache.hadoop.util.ReflectionUtils.newInstance（ReflectionUtils.java:115）
在org.apache.hadoop.mapred.MapTask.runNewMapper（MapTask.java:602）
在org.apache。 hadoop.mapred.MapTask.run（MapTask.java:323）在org.apache.hadoop.mapred.Child处
 $ 4.run（Child.java:270）$ java.util.AccessController.doPrivileged处
 （本地方法）
在javax.security.auth.Subject.doAs（Subject.java:396）
在org.apache.hadoop.security.UserGroup Information.doAs（UserGroupInformation.java:1177）
在org.apache.hadoop.mapred.Child.main（Child.java:264）
引起：java.lang.NoSuchMethodException：MaxTemperature $ MaxTemperatureMapper。 < init>（）
 at java.lang.Class.getConstructor0（Class.java:2706）$ b $ at java.lang.Class.getDeclaredConstructor（Class.java:1985）
 at org .apache.hadoop.util.ReflectionUtils.newInstance（ReflectionUtils.java:109）
 ... 7 more

这个错误是什么意思？我做错了什么，我该如何纠正？感谢！

解决方案

您的映射器和reducer类需要定义为static，否则compile会创建一个带有单个参数的构造函数父 MaxTemperature 类）。因此，现在不存在默认构造函数。

  public static class MaxTemperatureMapper extends Mapper< .... 
 
 public static class MaxTemperatureReducer extends Reducer< ....


I have written a MapReduce program, code is below:

import java.io.IOException;
import java.util.Iterator;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.Reporter;
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 MaxTemperature {

public class MaxTemperatureMapper extends Mapper <LongWritable, Text, Text, IntWritable>{
    private static final int MISSING = 9999;

    public void map(LongWritable key, Text Value, Context context, Reporter reporter) throws IOException, InterruptedException{
        String line = Value.toString();
        String year = line.substring(15,19);
        int airTemperature;
        if(line.charAt(87)=='+')
            airTemperature = Integer.parseInt(line.substring(88,92));
        else
            airTemperature = Integer.parseInt(line.substring(87,91));
        String quality = line.substring(92,93);
        if(airTemperature!=MISSING && quality.matches("[01459]"))
            context.write(new Text(year), new IntWritable(airTemperature));
    }
}

public class MaxTemperatureReducer extends Reducer<Text, IntWritable, Text, IntWritable>{
    public void reduce (Text Key, Iterator<IntWritable> Values, Context context, Reporter reporter) throws IOException, InterruptedException{

        int maxValue = Integer.MIN_VALUE;
        while(Values.hasNext())
            maxValue = Math.max(maxValue, Values.next().get());
        context.write(Key, new IntWritable(maxValue));

    }
}

public static void main(String[] args) throws Exception {
    if(args.length!=2){
        System.err.println("Usage: WeatherTemperature  <input path> <output path>");
        System.exit(-1);
    }
    Configuration conf = new Configuration();
    Job job = new Job(conf, "Maximum Temperature Calculator");
    job.setJarByClass(MaxTemperature.class);

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

    job.setMapperClass(MaxTemperatureMapper.class);
    job.setReducerClass(MaxTemperatureReducer.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);
    }
}

I run the .jar of this program using the following command:

hadoop jar weather.jar MaxTemperature input output

And I'm getting the following error:

12/06/13 00:52:05 INFO mapred.JobClient: Task Id :     attempt_201206121354_0007_m_000000_0, Status : FAILED
java.lang.RuntimeException: java.lang.NoSuchMethodException:      MaxTemperature$MaxTemperatureMapper.<init>()
    at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:115)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:602)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:323)
    at org.apache.hadoop.mapred.Child$4.run(Child.java:270)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:396)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1177)
    at org.apache.hadoop.mapred.Child.main(Child.java:264)
Caused by: java.lang.NoSuchMethodException: MaxTemperature$MaxTemperatureMapper.<init>()
    at java.lang.Class.getConstructor0(Class.java:2706)
    at java.lang.Class.getDeclaredConstructor(Class.java:1985)
    at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:109)
    ... 7 more

What does this error mean? And what am I doing wrong, how do I rectify it? Thanks!

解决方案

Your mapper and reducer classes need to be defined static, otherwise the compile creates a constructor with a single argument (the parent MaxTemperature class). Hence there now is not a default constructor.

public static class MaxTemperatureMapper extends Mapper<....

public static class MaxTemperatureReducer extends Reducer<....

这篇关于Hadoop：没有这样的方法例外的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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