BeanCopier 详解「建议收藏」

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 BeanCopier 实现属性拷贝的主要代码：
 BeanCopier beanCopier = BeanCopier.create(dad.getClass(), dadly.getClass(), false);
 beanCopier.copy(dad, dadly, null);
 
 查看BeanCopier源码可知：

abstract public class BeanCopier
{
    private static final BeanCopierKey KEY_FACTORY =
      (BeanCopierKey)KeyFactory.create(BeanCopierKey.class);
    private static final Type CONVERTER =
      TypeUtils.parseType("net.sf.cglib.core.Converter");
    private static final Type BEAN_COPIER =
      TypeUtils.parseType("net.sf.cglib.beans.BeanCopier");
    private static final Signature COPY =
      new Signature("copy", Type.VOID_TYPE, new Type[]{ Constants.TYPE_OBJECT, Constants.TYPE_OBJECT, CONVERTER });
    private static final Signature CONVERT =
      TypeUtils.parseSignature("Object convert(Object, Class, Object)");

BeanCopier为抽象类，并且：

abstract public void copy(Object from, Object to, Converter converter);

copy为抽象方法，在cglib的包里我们找不到
BeanCopier的实现类。

由此我们可以根据此行代码：

BeanCopier beanCopier = BeanCopier.create(dad.getClass(), dadly.getClass(), false);

并且：

public static BeanCopier create(Class source, Class target, boolean useConverter) {
        Generator gen = new Generator();
        gen.setSource(source);
        gen.setTarget(target);
        gen.setUseConverter(useConverter);
        return gen.create();
    }


public static class Generator extends AbstractClassGenerator {
  ....

  public BeanCopier create() {
            Object key = KEY_FACTORY.newInstance(source.getName(), target.getName(), useConverter);
            return (BeanCopier)super.create(key);
        }
  
   ...
}

由此可知：

beanCopier 的实际创建工作是由AbstractClassGenerator类的create（Class type）方法完成的，如下是此方法源码：

    protected Object create(Object key) {
        try {
        	Class gen = null;
        	
            synchronized (source) {
                ClassLoader loader = getClassLoader();
                Map cache2 = null;
                cache2 = (Map)source.cache.get(loader);
                if (cache2 == null) {
                    cache2 = new HashMap();
                    cache2.put(NAME_KEY, new HashSet());
                    source.cache.put(loader, cache2);
                } else if (useCache) {
                    Reference ref = (Reference)cache2.get(key);
                    gen = (Class) (( ref == null ) ? null : ref.get()); 
                }
                if (gen == null) {
                    Object save = CURRENT.get();
                    CURRENT.set(this);
                    try {
                        this.key = key;
                        
                        if (attemptLoad) {
                            try {
                                gen = loader.loadClass(getClassName());
                            } catch (ClassNotFoundException e) {
                                // ignore
                            }
                        }
                        if (gen == null) {
                            byte[] b = strategy.generate(this);
                            String className = ClassNameReader.getClassName(new ClassReader(b));
                            getClassNameCache(loader).add(className);
                            gen = ReflectUtils.defineClass(className, b, loader);
                        }
                       
                        if (useCache) {
                            cache2.put(key, new WeakReference(gen));
                        }
                        return firstInstance(gen);
                    } finally {
                        CURRENT.set(save);
                    }
                }
            }
            return firstInstance(gen);
        } catch (RuntimeException e) {
            throw e;
        } catch (Error e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        }
    }

熟悉cglib动态代理源码的都知道，此处代码就是cglib操作字节码生成动态代理类的主要实现方法。

所以beanCopier 实际上是BeanCopier的代理类，该代理类实现了 copy（）方法，即如何复制相同名称的属性。

以下是生成的动态代理类：

// Decompiled by DJ v3.7.7.81 Copyright 2004 Atanas Neshkov  Date: 2013/10/17 22:01:37
// Home Page : http://members.fortunecity.com/neshkov/dj.html  - Check often for new version!
// Decompiler options: packimports(3) 
// Source File Name:   <generated>

package proxy;

import net.sf.cglib.beans.BeanCopier;
import net.sf.cglib.core.Converter;

// Referenced classes of package proxy:
//            Dadly, Dad

public class Dadly$$BeanCopierByCGLIB$$a6acdbb5 extends BeanCopier
{

    public void copy(Object obj, Object obj1, Converter converter)
    {
        (Dadly)obj1;
        (Dad)obj;
        JVM INSTR dup2 ;
        getAge();
        setAge();
        JVM INSTR dup2 ;
        getName();
        setName();
    }

    public Dadly$$BeanCopierByCGLIB$$a6acdbb5()
    {
    }
}

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