一、前言

关于datanucleus-enhancer源码包中org.datanucleus.enhancer.EnhancerClassLoader增强型类加载器，实现指定自定义代理指定加载器类功能，主要包括defineClass、根据名称实例化loadClass、根据名称加载资源findResource功能方法，具体看源码说明。

二、源码说明

package org.datanucleus.enhancer;@b@@b@import java.net.URL;@b@import org.datanucleus.ClassLoaderResolver;@b@import org.datanucleus.exceptions.ClassNotResolvedException;@b@@b@public final class EnhancerClassLoader extends ClassLoader@b@{@b@  ClassLoaderResolver delegate;@b@  boolean loadingClass = false;@b@  boolean loadingResource = false;@b@@b@  public EnhancerClassLoader()@b@  {@b@    super(Thread.currentThread().getContextClassLoader());@b@  }@b@@b@  public EnhancerClassLoader(ClassLoaderResolver iDelegate)@b@  {@b@    this.delegate = iDelegate;@b@  }@b@@b@  public synchronized void defineClass(String fullClassName, byte[] bytes, ClassLoaderResolver clr)@b@  {@b@    ClassLoaderResolver oldDelegate = this.delegate;@b@    this.delegate = clr;@b@    try@b@    {@b@      defineClass(fullClassName, bytes, 0, bytes.length);@b@    }@b@    finally@b@    {@b@      this.delegate = oldDelegate;@b@    }@b@  }@b@@b@  public synchronized Class loadClass(String name)@b@    throws ClassNotFoundException@b@  {@b@    if (this.loadingClass)@b@    {@b@      throw new ClassNotFoundException("Class " + name + " not found");@b@    }@b@    this.loadingClass = true;@b@    try@b@    {@b@      if (this.delegate != null)@b@      {@b@        try@b@        {@b@          Class localClass1 = this.delegate.classForName(name);@b@@b@          this.loadingClass = false; return localClass1;@b@        }@b@        catch (ClassNotResolvedException cnrex)@b@        {@b@          throw new ClassNotFoundException(((ClassNotResolvedException)cnrex).toString(), (Throwable)cnrex);@b@        }@b@      }@b@      cnrex = super.loadClass(name);@b@@b@      return cnrex;@b@    }@b@    catch (ClassNotFoundException ex)@b@    {@b@      if (this.delegate != null);@b@      throw ex;@b@    }@b@    finally@b@    {@b@      this.loadingClass = false;@b@    }@b@  }@b@@b@  protected synchronized URL findResource(String name)@b@  {@b@    if (this.loadingResource)@b@    {@b@      return null;@b@    }@b@    this.loadingResource = true;@b@    try@b@    {@b@      URL url = super.findResource(name);@b@      if ((url == null) && @b@        (this.delegate != null))@b@      {@b@        url = this.delegate.getResource(name, null);@b@      }@b@@b@      URL localURL1 = url;@b@@b@      return localURL1; } finally { this.loadingResource = false;@b@    }@b@  }@b@}