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Jackson (https://github.com/FasterXML/jackson) extension module used to enhance performance using bytecode generation to replace use of Reflection for field access and method calls

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package com.fasterxml.jackson.module.afterburner.util;

import java.lang.reflect.Method;

/**
 * Class loader that is needed to load generated classes.
 */
public class MyClassLoader extends ClassLoader
{
    /**
     * Flag that determines if we should first try to load new class
     * using parent class loader or not; this may be done to try to
     * force access to protected/package-access properties.
     */
    protected final boolean _cfgUseParentLoader;
    
    public MyClassLoader(ClassLoader parent, boolean tryToUseParent)
    {
        super(parent);
        _cfgUseParentLoader = tryToUseParent;
    }
    
    /**
     * @param className Interface or abstract class that class to load should extend or 
     *   implement
     */
    public Class loadAndResolve(String className, byte[] byteCode)
        throws IllegalArgumentException
    {
        // First things first: just to be sure; maybe we have already loaded it?
        Class old = findLoadedClass(className);
        if (old != null) {
            return old;
        }
        
        Class impl;
        
        // First: let's try calling it directly on parent, to be able to access protected/package-access stuff:
        if (_cfgUseParentLoader) {
            try {
                Method method = ClassLoader.class.getDeclaredMethod("defineClass", 
                        new Class[] {String.class, byte[].class, int.class,
                        int.class});
                method.setAccessible(true);
                return (Class)method.invoke(getParent(),
                        new Object[] { className, byteCode, Integer.valueOf(0), Integer.valueOf(byteCode.length)});
            } catch (Exception e) { }
        }

        // but if that doesn't fly, try to do it from our own class loader
        try {
            impl = defineClass(className, byteCode, 0, byteCode.length);
        } catch (LinkageError e) {
            throw new IllegalArgumentException("Failed to load class '"+className+"': "+e.getMessage() ,e);
        }
        // important: must also resolve the class...
        resolveClass(impl);
        return impl;
    }
}