我编写了一个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.*;
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);
}
}
我使用以下命令运行该程序的.jar：
hadoop jar weather.jar MaxTemperature input output
我收到以下错误：
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
这个错误是什么意思？我做错了什么，我该如何纠正呢？谢谢！
答案 0 :(得分：34)
您的mapper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，现在没有默认的构造函数。
public static class MaxTemperatureMapper extends Mapper<....
public static class MaxTemperatureReducer extends Reducer<....
答案 1 :(得分：1)
我猜测Mapper没有默认构造函数，但这是MaxTemperatureMapper唯一的构造函数。
答案 2 :(得分：1)
我在scala中使用默认构造函数修复了类似错误KEY Mapper Reducer
15/05/12 01:07:57 WARN mapred.LocalJobRunner: job_local1713686765_0001
java.lang.Exception: java.io.IOException: Initialization of all the collectors failed. Error in last collector was :java.lang.NoSuchMethodException: IntPair.<init>()
at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:522)
Caused by: java.io.IOException: Initialization of all the collectors failed. Error in last collector was :java.lang.NoSuchMethodException: IntPair.<init>()
at org.apache.hadoop.mapred.MapTask.createSortingCollector(MapTask.java:414)
at org.apache.hadoop.mapred.MapTask.access$100(MapTask.java:81)
at org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:698)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:770)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:243)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
class IntPair (first : IntWritable, second : IntWritable) extends WritableComparable[IntPair] {
def this() = this(first = new IntWritable(), second = new IntWritable())
def getFirst () : IntWritable = {
first
}
def getSecond () : IntWritable = {
second
}
}