[HADOOP-12406] AbstractMapWritable.readFields throws ClassNotFoundException with custom writables

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 2.7.1
• Fix Version/s: 2.8.0, 2.7.3, 3.0.0-alpha1
• Component/s: io

Environment

Ubuntu Linux 14.04 LTS amd64

• Target Version/s: 2.8.0, 2.7.3
• Hadoop Flags: Reviewed
• Flags: Patch
• Assignee: Nadeem Douba
• Reporter: Nadeem Douba
• Created: 12/Sep/15 07:09
• Updated: 06/Feb/19 11:18
• Resolved: 11/Apr/16 19:06

Description

Note: I am not an expert at JAVA, Class loaders, or Hadoop. I am just a hacker. My solution might be entirely wrong.

AbstractMapWritable.readFields throws a ClassNotFoundException when reading custom writables. Debugging the job using remote debugging in IntelliJ revealed that the class loader being used in Class.forName() is different than that used by the Thread's current context (Thread.currentThread().getContextClassLoader()). The class path for the system class loader does not include the libraries of the job jar. However, the class path for the context class loader does. The proposed patch changes the class loading mechanism in readFields to use the Thread's context class loader instead of the system's default class loader.

Issue Links

• relates to: NUTCH-1084 ReadDB url throws exception
• links to: GitHub Pull Request #32