FAILED Error: java.io.IOException: Initialization

问题:

I am getting some error while running my MapReduce WordCount job.

Error: java.io.IOException: Initialization of all the collectors failed. Error in last collector was :class wordcount.wordmapper 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.YarnChild$2.run(YarnChild.java:164) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:415) atorg.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1693)at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158) Caused by: java.lang.ClassCastException: class wordcount.wordmapperat java.lang.Class.asSubclass(Class.java:3165)at org.apache.hadoop.mapred.JobConf.getOutputKeyComparator(JobConf.java:892) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.init(MapTask.java:1005) at org.apache.hadoop.mapred.MapTask.createSortingCollector(MapTask.java:402)

回答1:

I found that I had to implement WritableComparable<> interface for this to work.

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());
        }
    }

}

回答2:

Same thing happens with me while running a mapredue job.Please import the correct Text class.

If you have imported the below import, you will get that error:

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

Change it to this.

import org.apache.hadoop.io.Text;

回答3:

Your class must have a default constructor, if you have defined any parameterized constructor the default constructor automatically gets removed. You should explicitly define this constructor. Can you show your code snippet ?

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

  public SampleClass()
  {
  }
}