没有这样的方法异常 Hadoop <init>

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当我从命令提示符运行 Hadoop .jar 文件时，它抛出一个异常，说没有这样的方法 StockKey 方法.

When I am running a Hadoop .jar file from the command prompt, it throws an exception saying no such method StockKey method.

StockKey 是我为我自己的密钥类型定义的自定义类.

StockKey is my custom class defined for my own type of key.

这里有一个例外:

12/07/12 00:18:47 INFO mapred.JobClient: Task Id : attempt_201207082224_0007_m_000000_1, Status : FAILED java.lang.RuntimeException: java.lang.NoSuchMethodException: SecondarySort$StockKey. <init>() at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:115) at org.apache.hadoop.io.WritableComparator.newKey(WritableComparator.java:109) at org.apache.hadoop.io.WritableComparator.<init>(WritableComparator.java:95) at org.apache.hadoop.io.WritableComparator.get(WritableComparator.java:51) at org.apache.hadoop.mapred.JobConf.getOutputKeyComparator(JobConf.java:795) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.<init>(MapTask.java:817) at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:383) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:325) 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:1127) at org.apache.hadoop.mapred.Child.main(Child.java:264)

推荐答案

您必须在关键类中提供一个空的默认构造函数.Hadoop 正在使用反射，它无法猜测要馈送的任何参数.

You have to provide an empty default constructor in your key class. Hadoop is using reflection and it can not guess any parameters to feed.

所以只需添加默认构造函数:

So just add the default constructor:

public StockKey(){}