Mybatis源码-CglibProxyFactory(cglib工厂类)

Cglib 代理工厂类，为了实现延迟加载属性

1、源码（Cglib代理工厂类）

import java.lang.reflect.Method;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

import org.apache.ibatis.executor.loader.AbstractEnhancedDeserializationProxy;
import org.apache.ibatis.executor.loader.AbstractSerialStateHolder;
import org.apache.ibatis.executor.loader.ProxyFactory;
import org.apache.ibatis.executor.loader.ResultLoaderMap;
import org.apache.ibatis.executor.loader.WriteReplaceInterface;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;
import org.apache.ibatis.reflection.ExceptionUtil;
import org.apache.ibatis.reflection.factory.ObjectFactory;
import org.apache.ibatis.reflection.property.PropertyCopier;
import org.apache.ibatis.reflection.property.PropertyNamer;
import org.apache.ibatis.session.Configuration;

/**
 * cglib代理工厂类，实现延迟加载属性
 * @author Clinton Begin
 */
public class CglibProxyFactory implements ProxyFactory {

  /**
   * finalize方法
   */
  private static final String FINALIZE_METHOD = "finalize";
  /**
   * writeReplace方法
   */
  private static final String WRITE_REPLACE_METHOD = "writeReplace";

  /**
   * 加载Enhancer，这个是Cglib的入口
   */
  public CglibProxyFactory() {
    try {
      Resources.classForName("net.sf.cglib.proxy.Enhancer");
    } catch (Throwable e) {
      throw new IllegalStateException("Cannot enable lazy loading because CGLIB is not available. Add CGLIB to your classpath.", e);
    }
  }

  /**
   * 创建代理对象
   * @param target 目标对象
   * @param lazyLoader 延迟加载器
   * @param configuration 配置类
   * @param objectFactory 对象工厂
   * @param constructorArgTypes 构造函数类型[]
   * @param constructorArgs  构造函数的值[]
   * @return
   */
  @Override
  public Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    return EnhancedResultObjectProxyImpl.createProxy(target, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
  }

  /**
   * 创建一个反序列化代理
   * @param target 目标
   * @param unloadedProperties
   * @param objectFactory 对象工厂
   * @param constructorArgTypes 构造函数类型数组
   * @param constructorArgs 构造函数值
   * @return
   */
  public Object createDeserializationProxy(Object target, Map<String, ResultLoaderMap.LoadPair> unloadedProperties, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    return EnhancedDeserializationProxyImpl.createProxy(target, unloadedProperties, objectFactory, constructorArgTypes, constructorArgs);
  }

  @Override
  public void setProperties(Properties properties) {
      // Not Implemented
  }

  /**
   * 返回代理对象， 这个代理对象在调用任何方法都会调用本类的intercept方法
   * Enhancer 认为这个就是自定义类的工厂，比如这个类需要实现什么接口
   * @param type 目标类型
   * @param callback 结果对象代理实现类，当中有invoke回调方法
   * @param constructorArgTypes 构造函数类型数组
   * @param constructorArgs 构造函数对应字段的值数组
   * @return
   */
  static Object crateProxy(Class<?> type, Callback callback, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    // enhancer 配置调节代理对象的一些参数
    // 设置回调方法
    // 设置超类
    //判断当传入目标类型是否有writeReplace方法，没有则配置一个有writeReplace方法的接口（序列化写出）
    Enhancer enhancer = new Enhancer();
    enhancer.setCallback(callback);
    enhancer.setSuperclass(type);
    try {
      type.getDeclaredMethod(WRITE_REPLACE_METHOD);
      // ObjectOutputStream will call writeReplace of objects returned by writeReplace
      if (LogHolder.log.isDebugEnabled()) {
        LogHolder.log.debug(WRITE_REPLACE_METHOD + " method was found on bean " + type + ", make sure it returns this");
      }
    } catch (NoSuchMethodException e) {
      //这个enhancer增加一个WriteReplaceInterface接口
      enhancer.setInterfaces(new Class[]{WriteReplaceInterface.class});
    } catch (SecurityException e) {
      // nothing to do here
    }
    //根据构造函数创建一个对象
    //无参构造
    //有参构造
    Object enhanced;
    if (constructorArgTypes.isEmpty()) {
      enhanced = enhancer.create();
    } else {
      Class<?>[] typesArray = constructorArgTypes.toArray(new Class[constructorArgTypes.size()]);
      Object[] valuesArray = constructorArgs.toArray(new Object[constructorArgs.size()]);
      enhanced = enhancer.create(typesArray, valuesArray);
    }
    return enhanced;
  }

  /**
   * 结果对象代理实现类，
   * 它实现方法拦截器的intercept方法
   */
  private static class EnhancedResultObjectProxyImpl implements MethodInterceptor {

    private final Class<?> type;
    private final ResultLoaderMap lazyLoader;
    private final boolean aggressive;
    private final Set<String> lazyLoadTriggerMethods;
    private final ObjectFactory objectFactory;
    private final List<Class<?>> constructorArgTypes;
    private final List<Object> constructorArgs;

    /**
     * 代理对象创建
     * @param type 目标class类型
     * @param lazyLoader 延迟加载器
     * @param configuration 配置信息
     * @param objectFactory 对象工厂
     * @param constructorArgTypes 构造函数类型数组
     * @param constructorArgs 构造函数值数组
     */
    private EnhancedResultObjectProxyImpl(Class<?> type, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      this.type = type;
      this.lazyLoader = lazyLoader;
      this.aggressive = configuration.isAggressiveLazyLoading();
      this.lazyLoadTriggerMethods = configuration.getLazyLoadTriggerMethods();
      this.objectFactory = objectFactory;
      this.constructorArgTypes = constructorArgTypes;
      this.constructorArgs = constructorArgs;
    }

    /**
     * 创建代理对象, 将源对象值赋值给代理对象
     * @param target 目标对象
     * @param lazyLoader 延迟加载器
     * @param configuration 配置对象
     * @param objectFactory 对象工厂
     * @param constructorArgTypes 构造函数类型数组
     * @param constructorArgs 构造函数值数组
     * @return
     */
    public static Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      //获取目标的类型
      //创建一个结果对象代理实现类（它实现cglib的MethodInterface接口，完成回调作用invoke方法）
      final Class<?> type = target.getClass();
      EnhancedResultObjectProxyImpl callback = new EnhancedResultObjectProxyImpl(type, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
      Object enhanced = crateProxy(type, callback, constructorArgTypes, constructorArgs);
      PropertyCopier.copyBeanProperties(type, target, enhanced);
      return enhanced;
    }

    /**
     * 回调方法
     * @param enhanced 代理对象
     * @param method 方法
     * @param args 方法参数
     * @param methodProxy 代理方法
     * @return
     * @throws Throwable
     */
    @Override
    public Object intercept(Object enhanced, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
      //获取方法名
      final String methodName = method.getName();
      try {
        // 同步获取延迟加载对象
        // 如果是执行writeReplace方法(序列化写出）
        // 实例化一个目标对象的实例
        synchronized (lazyLoader) {
          if (WRITE_REPLACE_METHOD.equals(methodName)) {
            Object original;
            if (constructorArgTypes.isEmpty()) {
              original = objectFactory.create(type);
            } else {
              original = objectFactory.create(type, constructorArgTypes, constructorArgs);
            }
            // 将enhanced中的属性复制到orignal对象中
            // 如果延迟加载数量>0,
            PropertyCopier.copyBeanProperties(type, enhanced, original);
            if (lazyLoader.size() > 0) {
              return new CglibSerialStateHolder(original, lazyLoader.getProperties(), objectFactory, constructorArgTypes, constructorArgs);
            } else {
              return original;
            }
          } else {
            //不是writeReplace方法
            // 延迟加载长度大于0， 且不是finalize方法
            // configuration配置延迟加载参数，延迟加载触发的方法包含这个方法
            // 延迟加载所有数据
            if (lazyLoader.size() > 0 && !FINALIZE_METHOD.equals(methodName)) {
              if (aggressive || lazyLoadTriggerMethods.contains(methodName)) {
                lazyLoader.loadAll();
                // setter方法，直接移除
              } else if (PropertyNamer.isSetter(methodName)) {
                final String property = PropertyNamer.methodToProperty(methodName);
                lazyLoader.remove(property);
                // getter方法， 加载该属性
              } else if (PropertyNamer.isGetter(methodName)) {
                final String property = PropertyNamer.methodToProperty(methodName);
                if (lazyLoader.hasLoader(property)) {
                  lazyLoader.load(property);
                }
              }
            }
          }
        }
        return methodProxy.invokeSuper(enhanced, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
  }

  /**
   * 他继承抽象反序列化代理和实现了方法拦截
   */
  private static class EnhancedDeserializationProxyImpl extends AbstractEnhancedDeserializationProxy implements MethodInterceptor {

    private EnhancedDeserializationProxyImpl(Class<?> type, Map<String, ResultLoaderMap.LoadPair> unloadedProperties, ObjectFactory objectFactory,
            List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      super(type, unloadedProperties, objectFactory, constructorArgTypes, constructorArgs);
    }

    /**
     * 创建代理对象
     * @param target
     * @param unloadedProperties
     * @param objectFactory
     * @param constructorArgTypes
     * @param constructorArgs
     * @return
     */
    public static Object createProxy(Object target, Map<String, ResultLoaderMap.LoadPair> unloadedProperties, ObjectFactory objectFactory,
            List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      final Class<?> type = target.getClass();
      EnhancedDeserializationProxyImpl callback = new EnhancedDeserializationProxyImpl(type, unloadedProperties, objectFactory, constructorArgTypes, constructorArgs);
      Object enhanced = crateProxy(type, callback, constructorArgTypes, constructorArgs);
      PropertyCopier.copyBeanProperties(type, target, enhanced);
      return enhanced;
    }

    @Override
    public Object intercept(Object enhanced, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
      final Object o = super.invoke(enhanced, method, args);
      return o instanceof AbstractSerialStateHolder ? o : methodProxy.invokeSuper(o, args);
    }

    @Override
    protected AbstractSerialStateHolder newSerialStateHolder(Object userBean, Map<String, ResultLoaderMap.LoadPair> unloadedProperties, ObjectFactory objectFactory,
            List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      return new CglibSerialStateHolder(userBean, unloadedProperties, objectFactory, constructorArgTypes, constructorArgs);
    }
  }

  private static class LogHolder {
    private static final Log log = LogFactory.getLog(CglibProxyFactory.class);
  }

}

1.1、总结

1. 通过cglib创建代理对象，然后实现延迟加载数据，填充某个属性
2. 创建代理对象，每次代理调用方法实现，首先会调用MethodInterceptor的intercept方法