Question

运行MapReduce WordCount作业时出现错误。

错误：java.io.IOException：初始化所有收集器失败。最后一个收集器的错误是：class wordcount.wordmapper at org.apache.hadoop.mapred.MapTask.createSortingCollector（MapTask.java:414）在org.apache.hadoop.mapred.MapTask.access $ 100（MapTask.java:81）at org.apache.hadoop.mapred.YarnChild $ 2.run（YarnChild.java:164）at at java.security.AccessController.doPrivileged（Native Method）at javax.security.auth.Subject.doAs（Subject.java:415） atorg.apache.hadoop.security.UserGroupInformation.doAs（UserGroupInformation.java:1693）在 org.apache.hadoop.mapred.YarnChild.main（YarnChild.java:158）引起： java.lang.ClassCastException：class wordcount.wordmapperat java.lang.Class.asSubclass（Class.java:3165）在 org.apache.hadoop.mapred.JobConf.getOutputKeyComparator（JobConf.java:892）在 org.apache.hadoop.mapred.MapTask $ MapOutputBuffer.init（MapTask.java:1005）在 org.apache.hadoop.mapred.MapTask.createSortingCollector（MapTask.java:402）

Answer 1

我发现必须实现WritableComparable<>接口才能起作用。

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;
public class Pair implements WritableComparable<Pair> {

    public Text key1;

    public Text key2;

    public Pair() {
        key1 = new Text();
        key2 = new Text();
    }

    public Pair(String key1, String key2) {
        this.key1 = new Text(key1);
        this.key2 = new Text(key2);
    }

    public void setKey1(Text key1) {
        this.key1 = key1;
    }

    public void setKey2(Text key2) {
        this.key2 = key2;
    }

    public Text getKey1() {
        return key1;
    }

    public Text getKey2() {
        return key2;
    }

    @Override
    public boolean equals(Object b) {
        Pair p = (Pair) b;
        return p.key1.toString().equals(this.key1.toString())
                && p.key2.toString().equals(this.key2.toString());
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((key1 == null) ? 0 : key1.toString().hashCode());
        result = prime * result
                + ((key2 == null) ? 0 : key2.toString().hashCode());
        return result;
    }

    @Override
    public String toString() {
        return "(" + key1 + ", " + key2 + ")";
    }

    @Override
    public void readFields(DataInput arg0) throws IOException {
        key1.readFields(arg0);
        key2.readFields(arg0);
    }

    @Override
    public void write(DataOutput arg0) throws IOException {
        key1.write(arg0);
        key2.write(arg0);
    }

    public int compareTo(Pair p1) {
        int k = this.key1.toString().compareTo(p1.key1.toString());

        if (k != 0) {
            return k;
        } else {
            return this.key2.toString().compareTo(p1.key2.toString());
        }
    }

}

Answer 2

运行mapredue作业时，我也会发生同样的事情。请导入正确的Text类。

如果您导入了以下导入，则会收到该错误：

import com.sun.jersey.core.impl.provider.entity.XMLJAXBElementProvider.Text;

将其更改为此。

import org.apache.hadoop.io.Text;

Answer 3

您的类必须具有默认构造函数，如果已定义任何参数化构造函数，则会自动删除默认构造函数。您应该明确定义此构造函数。你能展示你的代码片段吗？

Class SampleClass
{
  int a;
  public SampleClass(int param)
  {
    a = param;
  }

  public SampleClass()
  {
  }
}

FAILED错误：java.io.IOException：所有收集器的初始化失败

3 个答案: