Mybatis源碼-CglibProxyFactory(cglib工廠類)

Cglib 代理工廠類，爲了實現延遲加載屬性

1、源碼（Cglib代理工廠類）

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代理工廠類，實現延遲加載屬性
 * @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";

  /**
   * 加載Enhancer，這個是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);
    }
  }

  /**
   * 創建代理對象
   * @param target 目標對象
   * @param lazyLoader 延遲加載器
   * @param configuration 配置類
   * @param objectFactory 對象工廠
   * @param constructorArgTypes 構造函數類型[]
   * @param constructorArgs  構造函數的值[]
   * @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);
  }

  /**
   * 創建一個反序列化代理
   * @param target 目標
   * @param unloadedProperties
   * @param objectFactory 對象工廠
   * @param constructorArgTypes 構造函數類型數組
   * @param constructorArgs 構造函數值
   * @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
  }

  /**
   * 返回代理對象， 這個代理對象在調用任何方法都會調用本類的intercept方法
   * Enhancer 認爲這個就是自定義類的工廠，比如這個類需要實現什麼接口
   * @param type 目標類型
   * @param callback 結果對象代理實現類，當中有invoke回調方法
   * @param constructorArgTypes 構造函數類型數組
   * @param constructorArgs 構造函數對應字段的值數組
   * @return
   */
  static Object crateProxy(Class<?> type, Callback callback, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    // enhancer 配置調節代理對象的一些參數
    // 設置回調方法
    // 設置超類
    //判斷當傳入目標類型是否有writeReplace方法，沒有則配置一個有writeReplace方法的接口（序列化寫出）
    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) {
      //這個enhancer增加一個WriteReplaceInterface接口
      enhancer.setInterfaces(new Class[]{WriteReplaceInterface.class});
    } catch (SecurityException e) {
      // nothing to do here
    }
    //根據構造函數創建一個對象
    //無參構造
    //有參構造
    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;
  }

  /**
   * 結果對象代理實現類，
   * 它實現方法攔截器的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;

    /**
     * 代理對象創建
     * @param type 目標class類型
     * @param lazyLoader 延遲加載器
     * @param configuration 配置信息
     * @param objectFactory 對象工廠
     * @param constructorArgTypes 構造函數類型數組
     * @param constructorArgs 構造函數值數組
     */
    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;
    }

    /**
     * 創建代理對象, 將源對象值賦值給代理對象
     * @param target 目標對象
     * @param lazyLoader 延遲加載器
     * @param configuration 配置對象
     * @param objectFactory 對象工廠
     * @param constructorArgTypes 構造函數類型數組
     * @param constructorArgs 構造函數值數組
     * @return
     */
    public static Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      //獲取目標的類型
      //創建一個結果對象代理實現類（它實現cglib的MethodInterface接口，完成回調作用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;
    }

    /**
     * 回調方法
     * @param enhanced 代理對象
     * @param method 方法
     * @param args 方法參數
     * @param methodProxy 代理方法
     * @return
     * @throws Throwable
     */
    @Override
    public Object intercept(Object enhanced, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
      //獲取方法名
      final String methodName = method.getName();
      try {
        // 同步獲取延遲加載對象
        // 如果是執行writeReplace方法(序列化寫出）
        // 實例化一個目標對象的實例
        synchronized (lazyLoader) {
          if (WRITE_REPLACE_METHOD.equals(methodName)) {
            Object original;
            if (constructorArgTypes.isEmpty()) {
              original = objectFactory.create(type);
            } else {
              original = objectFactory.create(type, constructorArgTypes, constructorArgs);
            }
            // 將enhanced中的屬性複製到orignal對象中
            // 如果延遲加載數量>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
            // 延遲加載長度大於0， 且不是finalize方法
            // configuration配置延遲加載參數，延遲加載觸發的方法包含這個方法
            // 延遲加載所有數據
            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， 加載該屬性
              } 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);
      }
    }
  }

  /**
   * 他繼承抽象反序列化代理和實現了方法攔截
   */
  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);
    }

    /**
     * 創建代理對象
     * @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、總結

1. 通過cglib創建代理對象，然後實現延遲加載數據，填充某個屬性
2. 創建代理對象，每次代理調用方法實現，首先會調用MethodInterceptor的intercept方法