org.apache.hadoop.hbase.util
Class DynamicClassLoader

java.lang.Object
  java.lang.ClassLoader
      java.security.SecureClassLoader
          java.net.URLClassLoader
              org.apache.hadoop.hbase.util.ClassLoaderBase
                  org.apache.hadoop.hbase.util.DynamicClassLoader

@InterfaceAudience.Private
public class DynamicClassLoader
extends ClassLoaderBase

This is a class loader that can load classes dynamically from new jar files under a configured folder. The paths to the jar files are converted to URLs, and URLClassLoader logic is actually used to load classes. This class loader always uses its parent class loader to load a class at first. Only if its parent class loader can not load a class, we will try to load it using the logic here.

The configured folder can be a HDFS path. In this case, the jar files under that folder will be copied to local at first under ${hbase.local.dir}/jars/. The local copy will be updated if the remote copy is updated, according to its last modified timestamp.

We can't unload a class already loaded. So we will use the existing jar files we already know to load any class which can't be loaded using the parent class loader. If we still can't load the class from the existing jar files, we will check if any new jar file is added, if so, we will load the new jar file and try to load the class again. If still failed, a class not found exception will be thrown.

Be careful in uploading new jar files and make sure all classes are consistent, otherwise, we may not be able to load your classes properly.

Field Summary

Fields inherited from class org.apache.hadoop.hbase.util.ClassLoaderBase

DEFAULT_LOCAL_DIR, LOCAL_DIR_KEY, parent

Constructor Summary

DynamicClassLoader(org.apache.hadoop.conf.Configuration conf, ClassLoader parent)
Creates a DynamicClassLoader that can load classes dynamically from jar files under a specific folder.

Method Summary

Class<?>

loadClass(String name)

Methods inherited from class org.apache.hadoop.hbase.util.ClassLoaderBase

getClassLoadingLock

Methods inherited from class java.net.URLClassLoader

addURL, definePackage, findClass, findResource, findResources, getPermissions, getURLs, newInstance, newInstance

Methods inherited from class java.security.SecureClassLoader

defineClass, defineClass

Methods inherited from class java.lang.ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findLibrary, findLoadedClass, findSystemClass, getPackage, getPackages, getParent, getResource, getResourceAsStream, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, loadClass, resolveClass, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DynamicClassLoader

public DynamicClassLoader(org.apache.hadoop.conf.Configuration conf,
                          ClassLoader parent)

Creates a DynamicClassLoader that can load classes dynamically from jar files under a specific folder.

Parameters:

conf - the configuration for the cluster.

parent - the parent ClassLoader to set.

Method Detail

loadClass

public Class<?> loadClass(String name)
                   throws ClassNotFoundException

Overrides:

loadClass in class ClassLoader

Throws:

ClassNotFoundException