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From "Paul Burkhardt (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-1686) ClassNotFoundException for custom format classes provided in libjars
Date Thu, 08 Apr 2010 16:31:36 GMT
ClassNotFoundException for custom format classes provided in libjars

                 Key: MAPREDUCE-1686
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1686
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: contrib/streaming
    Affects Versions: 0.20.2
            Reporter: Paul Burkhardt
            Priority: Trivial

The StreamUtil::goodClassOrNull method assumes user-provided classes have package names and
if not, they are part of the Hadoop Streaming package. For example, using custom InputFormat
or OutputFormat classes without package names will fail with a ClassNotFound exception which
is not indicative given the classes are provided in the libjars option. Admittedly, most Java
packages should have a package name so this should rarely come up.

Possible resolution options:

1) modify the error message to include the actual classname that was attempted in the goodClassOrNull
2) call the Configuration::getClassByName method first and if class not found check for default
package name and try the call again
    public static Class goodClassOrNull(Configuration conf, String className, String defaultPackage)
        Class clazz = null;
        try {
            clazz = conf.getClassByName(className);
        } catch (ClassNotFoundException cnf) {
        if (clazz == null) {
            if (className.indexOf('.') == -1 && defaultPackage != null) {
                className = defaultPackage + "." + className;
                try {
                    clazz = conf.getClassByName(className);
                } catch (ClassNotFoundException cnf) {
        return clazz;

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