Please help, don't know how to solve--java.io.IOException: WritableName can't load class

[Mudong Lu <qd...@gmail.com>]

Hello, guys,

I am very new to hadoop. I was trying to read nutch data files using a
script i found on http://wiki.apache.org/nutch/Getting_Started . And after 2
days of trying, I still cannot get it to work. now the error i got is
"java.lang.RuntimeException: java.io.IOException: WritableName can't load
class".

Below is my script:



/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package test;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.MapFile;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;


/**
 *
 * @author mudong
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        try{
            Configuration conf = new Configuration();
            conf.addResource(new
Path("/home/mudong/programming/java/hadoop-0.17.2.1/conf/hadoop-default.xml"));
            //conf.addResource(new
Path("/home/mudong/programming/java/hadoop-0.18.1/conf/hadoop-default.xml"));
            FileSystem fs= FileSystem.get(conf);
            String seqFile = new
String("/home/mudong/programming/java/nutch-0.9/crawl/segments/20081021075837/content/part-00000");
            MapFile.Reader reader;
            reader = new MapFile.Reader (fs, seqFile, conf);
            Class keyC = reader.getKeyClass();
            Class valueC = reader.getValueClass();

            while (true) {
                WritableComparable key = null;
                Writable value = null;
                try {
                    key = (WritableComparable)keyC.newInstance();
                    value = (Writable)valueC.newInstance();
                } catch (Exception ex) {
                    ex.printStackTrace();
                    System.exit(-1);
                }

                try {
                    if (!reader.next(key, value)) {
                        break;
                    }

                    System.out.println(key);
                    System.out.println(value);
                } catch (Exception e) {
                    e.printStackTrace();
                    System.out.println("Exception occured. " + e);
                    break;
                }
            }
        }catch(Exception e){
            e.printStackTrace();
            System.out.println("Exception occured. " + e);
        }
    }
}


And when I running the script above, I got error messages like below.

java.lang.RuntimeException: java.io.IOException: WritableName can't load
class
        at
org.apache.hadoop.io.SequenceFile$Reader.getValueClass(SequenceFile.java:1612)
Exception occured. java.lang.RuntimeException: java.io.IOException:
WritableName can't load class
        at
org.apache.hadoop.io.MapFile$Reader.getValueClass(MapFile.java:248)
        at test.Main.main(Main.java:36)
Caused by: java.io.IOException: WritableName can't load class
        at org.apache.hadoop.io.WritableName.getClass(WritableName.java:74)
        at
org.apache.hadoop.io.SequenceFile$Reader.getValueClass(SequenceFile.java:1610)
        ... 2 more
Caused by: java.lang.ClassNotFoundException:
org.apache.nutch.protocol.Content
        at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:247)
        at
org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:581)
        at org.apache.hadoop.io.WritableName.getClass(WritableName.java:72)

I've tried a lot of things, but it's just not working. I use
hadoop-0.17.2.1. Thanks a lot, guys,

Rongdong