mybatis源代码分析：mybatis延迟加载机制改进

在上一篇博客《mybatis源代码分析：深入了解mybatis延迟加载机制》讲诉了mybatis延迟加载的具体机制及实现原理。

可以看出，如果查询结果对象中有一个属性是需要延迟加载的，那整个结果对象就是一个代理对象，后面对这个对象的访问，都是通过代理对象去访问的，那是否有更好的方法呢？

答案是有的。

Student对象关联Teacher对象，需要对Teacher对象延迟加载。

一种方式就是mybatis当前的这种做法，对Student进行代理，当访问到getTeacher时就进行延迟加载，设置其teacher对象；

还有一种方式就是对teacher对象进行代理，当第一次加载之后，就将Student对象关联的teacher对象替换为真实的对象，而不再使用代理对象，这样后面对Student及Teacher的访问，就都是访问的实际对象，而不是代理对象了。

修改之后的代码：http://download.csdn.net/detail/u014569459/7372195

关键修改点说明：

1.修改org\apache\ibatis\executor\resultset\DefaultResultSetHandler.java类，注销掉里面生成代理对象的代码

  private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, ResultLoaderMap lazyLoader, String columnPrefix) throws SQLException {
    final List<Class<?>> constructorArgTypes = new ArrayList<Class<?>>();
    final List<Object> constructorArgs = new ArrayList<Object>();
    final Object resultObject = createResultObject(rsw, resultMap, constructorArgTypes, constructorArgs, columnPrefix);
    //comment by jerry
//        if (resultObject != null && !typeHandlerRegistry.hasTypeHandler(resultMap.getType())) {
//      final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
//      for (ResultMapping propertyMapping : propertyMappings) {
//        if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) { // issue gcode #109 && issue #149
//          return configuration.getProxyFactory().createProxy(resultObject, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
//        }
//      }
//    }
    return resultObject;
  }

2.修改org\apache\ibatis\executor\loader\cglib\CglibProxyFactory.java类

1）在createProxy方法增加两个参数Object parentObj,String fieldNameInParent，用于访问父对象。

  public Object createProxy(Object parentObj,String fieldNameInParent,Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    return EnhancedResultObjectProxyImpl.createProxy(parentObj,fieldNameInParent,target, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
  }

2）在EnhancedResultObjectProxyImpl类中，增加parentObj和属性，并修改默认构造函数。

    private Object parentObj;
    private String fieldNameInParent;

    private EnhancedResultObjectProxyImpl(Object parentObj,String fieldNameInParent,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;
      this.parentObj = parentObj;
      this.fieldNameInParent = fieldNameInParent;
    }

3）修改intercept函数

        if(parentObj!=null)
        {
            Field field = parentObj.getClass().getDeclaredField(fieldNameInParent);
            Object obj = field.get(parentObj);
            return method.invoke(obj, args);
        }
        else
        {
        	return methodProxy.invokeSuper(enhanced, args);
        }

修改文件列表（共4个）：

1.CglibProxyFactory.java

/*
 *    Copyright 2009-2013 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor.loader.cglib;

import java.lang.reflect.Field;
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;

/**
 * @author Clinton Begin
 */
public class CglibProxyFactory implements ProxyFactory {

  private static final Log log = LogFactory.getLog(CglibProxyFactory.class);
  private static final String FINALIZE_METHOD = "finalize";
  private static final String WRITE_REPLACE_METHOD = "writeReplace";

  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);
    }
  }

  public Object createProxy(Object parentObj,String fieldNameInParent,Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    return EnhancedResultObjectProxyImpl.createProxy(parentObj,fieldNameInParent,target, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
  }
  public Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    return EnhancedResultObjectProxyImpl.createProxy(null,null,target, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
  }

  public Object createDeserializationProxy(Object target, Map<String, ResultLoaderMap.LoadPair> unloadedProperties, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    return EnhancedDeserializationProxyImpl.createProxy(null,null,target, unloadedProperties, objectFactory, constructorArgTypes, constructorArgs);
  }

  public void setProperties(Properties properties) {
  }

  private static Object crateProxy(Class<?> type, Callback callback, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    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
      log.debug(WRITE_REPLACE_METHOD + " method was found on bean " + type + ", make sure it returns this");
    } catch (NoSuchMethodException e) {
      enhancer.setInterfaces(new Class[]{WriteReplaceInterface.class});
    } catch (SecurityException e) {
      // nothing to do here
    }
    Object enhanced = null;
    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;
  }

  private static class EnhancedResultObjectProxyImpl implements MethodInterceptor {

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

    private EnhancedResultObjectProxyImpl(Object parentObj,String fieldNameInParent,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;
      this.parentObj = parentObj;
      this.fieldNameInParent = fieldNameInParent;
    }

    public static Object createProxy(Object parentObj,String fieldNameInParent,Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {

      final Class<?> type = target.getClass();
      EnhancedResultObjectProxyImpl callback = new EnhancedResultObjectProxyImpl(parentObj,fieldNameInParent,type, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
      Object enhanced = crateProxy(type, callback, constructorArgTypes, constructorArgs);
      PropertyCopier.copyBeanProperties(type, target, enhanced);
      return enhanced;
    }

    public Object intercept(Object enhanced, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
      final String methodName = method.getName();
      try {
        synchronized (lazyLoader) {
          if (WRITE_REPLACE_METHOD.equals(methodName)) {
            Object original = null;
            if (constructorArgTypes.isEmpty()) {
              original = objectFactory.create(type);
            } else {
              original = objectFactory.create(type, constructorArgTypes, constructorArgs);
            }
            PropertyCopier.copyBeanProperties(type, enhanced, original);
            if (lazyLoader.size() > 0) {
              return new CglibSerialStateHolder(original, lazyLoader.getProperties(), objectFactory, constructorArgTypes, constructorArgs);
            } else {
              return original;
            }
          } else {
            if (lazyLoader.size() > 0 && !FINALIZE_METHOD.equals(methodName)) {
              if (aggressive || lazyLoadTriggerMethods.contains(methodName)) {
                lazyLoader.loadAll();
              } else if (PropertyNamer.isProperty(methodName)) {
                final String property = PropertyNamer.methodToProperty(methodName);
                if (lazyLoader.hasLoader(property)) {
                  lazyLoader.load(property);
                }
              }
            }
          }
        }

        if(parentObj!=null)
        {
            Field field = parentObj.getClass().getDeclaredField(fieldNameInParent);
            Object obj = field.get(parentObj);
            return method.invoke(obj, args);
        }
        else
        {
        	return methodProxy.invokeSuper(enhanced, args);
        }
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
  }

  private static class EnhancedDeserializationProxyImpl extends AbstractEnhancedDeserializationProxy implements MethodInterceptor {

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

    public static Object createProxy(Object parentObj,String fieldNameInParent,Object target, Map<String, ResultLoaderMap.LoadPair> unloadedProperties, ObjectFactory objectFactory,
            List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      final Class<?> type = target.getClass();
      EnhancedDeserializationProxyImpl callback = new EnhancedDeserializationProxyImpl(parentObj,fieldNameInParent,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);
    }
  }
}

2.JavassistProxyFactory.java

/*
 *    Copyright 2009-2012 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor.loader.javassist;

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

import javassist.util.proxy.MethodHandler;
import javassist.util.proxy.Proxy;
import javassist.util.proxy.ProxyFactory;

import org.apache.ibatis.executor.ExecutorException;
import org.apache.ibatis.executor.loader.AbstractEnhancedDeserializationProxy;
import org.apache.ibatis.executor.loader.AbstractSerialStateHolder;
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;

/**
 * @author Eduardo Macarron
 */
public class JavassistProxyFactory implements org.apache.ibatis.executor.loader.ProxyFactory {

  private static final Log log = LogFactory.getLog(JavassistProxyFactory.class);
  private static final String FINALIZE_METHOD = "finalize";
  private static final String WRITE_REPLACE_METHOD = "writeReplace";

  public JavassistProxyFactory() {
    try {
      Resources.classForName("javassist.util.proxy.ProxyFactory");
    } catch (Throwable e) {
      throw new IllegalStateException("Cannot enable lazy loading because Javassist is not available. Add Javassist to your classpath.", e);
    }
  }

  public Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
    return EnhancedResultObjectProxyImpl.createProxy(null,null,target, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
  }
  public Object createProxy(Object parentObj, String fieldNameInParent,Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
	    return EnhancedResultObjectProxyImpl.createProxy(parentObj,fieldNameInParent,target, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
  }

  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);
  }

  public void setProperties(Properties properties) {
  }

  private static Object crateProxy(Class<?> type, MethodHandler callback, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {

    ProxyFactory enhancer = new ProxyFactory();
    enhancer.setSuperclass(type);

    try {
      type.getDeclaredMethod(WRITE_REPLACE_METHOD);
      // ObjectOutputStream will call writeReplace of objects returned by writeReplace
      log.debug(WRITE_REPLACE_METHOD + " method was found on bean " + type + ", make sure it returns this");
    } catch (NoSuchMethodException e) {
      enhancer.setInterfaces(new Class[]{WriteReplaceInterface.class});
    } catch (SecurityException e) {
      // nothing to do here
    }

    Object enhanced = null;
    Class<?>[] typesArray = constructorArgTypes.toArray(new Class[constructorArgTypes.size()]);
    Object[] valuesArray = constructorArgs.toArray(new Object[constructorArgs.size()]);
    try {
      enhanced = enhancer.create(typesArray, valuesArray);
    } catch (Exception e) {
      throw new ExecutorException("Error creating lazy proxy.  Cause: " + e, e);
    }
    ((Proxy) enhanced).setHandler(callback);
    return enhanced;
  }

  private static class EnhancedResultObjectProxyImpl implements MethodHandler {

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

    private EnhancedResultObjectProxyImpl(Object parentObj, String fieldNameInParent,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;
      this.parentObj = parentObj;
      this.fieldNameInParent = fieldNameInParent;
    }

    public static Object createProxy(Object parentObj, String fieldNameInParent,Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
      final Class<?> type = target.getClass();
      EnhancedResultObjectProxyImpl callback = new EnhancedResultObjectProxyImpl(parentObj, fieldNameInParent,type, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
      Object enhanced = crateProxy(type, callback, constructorArgTypes, constructorArgs);
      PropertyCopier.copyBeanProperties(type, target, enhanced);
      return enhanced;
    }

    public Object invoke(Object enhanced, Method method, Method methodProxy, Object[] args) throws Throwable {
      final String methodName = method.getName();
      try {
        synchronized (lazyLoader) {
          if (WRITE_REPLACE_METHOD.equals(methodName)) {
            Object original = null;
            if (constructorArgTypes.isEmpty()) {
              original = objectFactory.create(type);
            } else {
              original = objectFactory.create(type, constructorArgTypes, constructorArgs);
            }
            PropertyCopier.copyBeanProperties(type, enhanced, original);
            if (lazyLoader.size() > 0) {
              return new JavassistSerialStateHolder(original, lazyLoader.getProperties(), objectFactory, constructorArgTypes, constructorArgs);
            } else {
              return original;
            }
          } else {
            if (lazyLoader.size() > 0 && !FINALIZE_METHOD.equals(methodName)) {
              if (aggressive || lazyLoadTriggerMethods.contains(methodName)) {
                lazyLoader.loadAll();
              } else if (PropertyNamer.isProperty(methodName)) {
                final String property = PropertyNamer.methodToProperty(methodName);
                if (lazyLoader.hasLoader(property)) {
                  lazyLoader.load(property);
                }
              }
            }
          }
        }
        if(parentObj!=null)
        {
            Field field = parentObj.getClass().getDeclaredField(fieldNameInParent);
            Object obj = field.get(parentObj);
            return method.invoke(obj, args);
        }
        else
        {
        	return methodProxy.invoke(enhanced, args);
        }
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
  }

  private static class EnhancedDeserializationProxyImpl extends AbstractEnhancedDeserializationProxy implements MethodHandler {

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

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

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

}

3.ProxyFactory.java

/*
 *    Copyright 2012 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor.loader;

import java.util.List;
import java.util.Properties;

import org.apache.ibatis.reflection.factory.ObjectFactory;
import org.apache.ibatis.session.Configuration;

/**
 * @author Eduardo Macarron
 */
public interface ProxyFactory {

  void setProperties(Properties properties);

  Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs);
  Object createProxy(Object parentObj,String fieldNameInParent,Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs);

}

4.DefaultResultSetHandler.java

/*
 *    Copyright 2009-2014 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor.resultset;

import java.sql.CallableStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;

import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.executor.ExecutorException;
import org.apache.ibatis.executor.loader.ResultLoader;
import org.apache.ibatis.executor.loader.ResultLoaderMap;
import org.apache.ibatis.executor.parameter.ParameterHandler;
import org.apache.ibatis.executor.result.DefaultResultContext;
import org.apache.ibatis.executor.result.DefaultResultHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.Discriminator;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.mapping.ParameterMode;
import org.apache.ibatis.mapping.ResultMap;
import org.apache.ibatis.mapping.ResultMapping;
import org.apache.ibatis.reflection.MetaClass;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.factory.ObjectFactory;
import org.apache.ibatis.session.AutoMappingBehavior;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultContext;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.type.TypeHandler;
import org.apache.ibatis.type.TypeHandlerRegistry;

/**
 * @author Clinton Begin
 * @author Eduardo Macarron
 */
public class DefaultResultSetHandler implements ResultSetHandler {

  private static final Object NO_VALUE = new Object();

  private final Executor executor;
  private final Configuration configuration;
  private final MappedStatement mappedStatement;
  private final RowBounds rowBounds;
  private final ParameterHandler parameterHandler;
  private final ResultHandler resultHandler;
  private final BoundSql boundSql;
  private final TypeHandlerRegistry typeHandlerRegistry;
  private final ObjectFactory objectFactory;

  // nested resultmaps
  private final Map<CacheKey, Object> nestedResultObjects = new HashMap<CacheKey, Object>();
  private final Map<CacheKey, Object> ancestorObjects = new HashMap<CacheKey, Object>();
  private final Map<String, String> ancestorColumnPrefix = new HashMap<String, String>();

  // multiple resultsets
  private final Map<String, ResultMapping> nextResultMaps = new HashMap<String, ResultMapping>();
  private final Map<CacheKey, PendingRelation> pendingRelations = new HashMap<CacheKey, PendingRelation>();

  private static class PendingRelation {
    public MetaObject metaObject;
    public ResultMapping propertyMapping;
  }

  public DefaultResultSetHandler(Executor executor, MappedStatement mappedStatement, ParameterHandler parameterHandler, ResultHandler resultHandler, BoundSql boundSql,
      RowBounds rowBounds) {
    this.executor = executor;
    this.configuration = mappedStatement.getConfiguration();
    this.mappedStatement = mappedStatement;
    this.rowBounds = rowBounds;
    this.parameterHandler = parameterHandler;
    this.boundSql = boundSql;
    this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
    this.objectFactory = configuration.getObjectFactory();
    this.resultHandler = resultHandler;
  }

  //
  // HANDLE OUTPUT PARAMETER
  //

  public void handleOutputParameters(CallableStatement cs) throws SQLException {
    final Object parameterObject = parameterHandler.getParameterObject();
    final MetaObject metaParam = configuration.newMetaObject(parameterObject);
    final List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
    for (int i = 0; i < parameterMappings.size(); i++) {
      final ParameterMapping parameterMapping = parameterMappings.get(i);
      if (parameterMapping.getMode() == ParameterMode.OUT || parameterMapping.getMode() == ParameterMode.INOUT) {
        if (ResultSet.class.equals(parameterMapping.getJavaType())) {
          handleRefCursorOutputParameter((ResultSet) cs.getObject(i + 1), parameterMapping, metaParam);
        } else {
          final TypeHandler<?> typeHandler = parameterMapping.getTypeHandler();
          metaParam.setValue(parameterMapping.getProperty(), typeHandler.getResult(cs, i + 1));
        }
      }
    }
  }

  private void handleRefCursorOutputParameter(ResultSet rs, ParameterMapping parameterMapping, MetaObject metaParam) throws SQLException {
    try {
      final String resultMapId = parameterMapping.getResultMapId();
      final ResultMap resultMap = configuration.getResultMap(resultMapId);
      final DefaultResultHandler resultHandler = new DefaultResultHandler(objectFactory);
      final ResultSetWrapper rsw = new ResultSetWrapper(rs, configuration);
      handleRowValues(rsw, resultMap, resultHandler, new RowBounds(), null);
      metaParam.setValue(parameterMapping.getProperty(), resultHandler.getResultList());
    } finally {
      closeResultSet(rs); // issue #228 (close resultsets)
    }
  }

  //
  // HANDLE RESULT SETS
  //

  public List<Object> handleResultSets(Statement stmt) throws SQLException {
    final List<Object> multipleResults = new ArrayList<Object>();

    int resultSetCount = 0;
    ResultSetWrapper rsw = getFirstResultSet(stmt);

    List<ResultMap> resultMaps = mappedStatement.getResultMaps();
    int resultMapCount = resultMaps.size();
    validateResultMapsCount(rsw, resultMapCount);
    while (rsw != null && resultMapCount > resultSetCount) {
      ResultMap resultMap = resultMaps.get(resultSetCount);
      handleResultSet(rsw, resultMap, multipleResults, null);
      rsw = getNextResultSet(stmt);
      cleanUpAfterHandlingResultSet();
      resultSetCount++;
    }

    String[] resultSets = mappedStatement.getResulSets();
    if (resultSets != null) {
      while (rsw != null && resultSetCount < resultSets.length) {
        ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
        if (parentMapping != null) {
          String nestedResultMapId = parentMapping.getNestedResultMapId();
          ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
          handleResultSet(rsw, resultMap, null, parentMapping);
        }
        rsw = getNextResultSet(stmt);
        cleanUpAfterHandlingResultSet();
        resultSetCount++;
      }
    }

    return collapseSingleResultList(multipleResults);
  }

  private ResultSetWrapper getFirstResultSet(Statement stmt) throws SQLException {
    ResultSet rs = stmt.getResultSet();
    while (rs == null) {
      // move forward to get the first resultset in case the driver
      // doesn't return the resultset as the first result (HSQLDB 2.1)
      if (stmt.getMoreResults()) {
        rs = stmt.getResultSet();
      } else {
        if (stmt.getUpdateCount() == -1) {
          // no more results. Must be no resultset
          break;
        }
      }
    }
    return rs != null ? new ResultSetWrapper(rs, configuration) : null;
  }

  private ResultSetWrapper getNextResultSet(Statement stmt) throws SQLException {
    // Making this method tolerant of bad JDBC drivers
    try {
      if (stmt.getConnection().getMetaData().supportsMultipleResultSets()) {
        // Crazy Standard JDBC way of determining if there are more results
        if (!((!stmt.getMoreResults()) && (stmt.getUpdateCount() == -1))) {
          ResultSet rs = stmt.getResultSet();
          return rs != null ? new ResultSetWrapper(rs, configuration) : null;
        }
      }
    } catch (Exception e) {
      // Intentionally ignored.
    }
    return null;
  }

  private void closeResultSet(ResultSet rs) {
    try {
      if (rs != null) {
        rs.close();
      }
    } catch (SQLException e) {
      // ignore
    }
  }

  private void cleanUpAfterHandlingResultSet() {
    nestedResultObjects.clear();
    ancestorColumnPrefix.clear();
  }

  private void validateResultMapsCount(ResultSetWrapper rsw, int resultMapCount) {
    if (rsw != null && resultMapCount < 1) {
      throw new ExecutorException("A query was run and no Result Maps were found for the Mapped Statement '" + mappedStatement.getId()
          + "'.  It's likely that neither a Result Type nor a Result Map was specified.");
    }
  }

  private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {
    try {
      if (parentMapping != null) {
        handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
      } else {
        if (resultHandler == null) {
          DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
          handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
          multipleResults.add(defaultResultHandler.getResultList());
        } else {
          handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);
        }
      }
    } finally {
      closeResultSet(rsw.getResultSet()); // issue #228 (close resultsets)
    }
  }

  private List<Object> collapseSingleResultList(List<Object> multipleResults) {
    if (multipleResults.size() == 1) {
      @SuppressWarnings("unchecked")
      List<Object> returned = (List<Object>) multipleResults.get(0);
      return returned;
    }
    return multipleResults;
  }

  //
  // HANDLE ROWS FOR SIMPLE RESULTMAP
  //

  private void handleRowValues(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
    if (resultMap.hasNestedResultMaps()) {
      ensureNoRowBounds();
      checkResultHandler();
      handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
    } else {
      handleRowValuesForSimpleResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
    }
  }  

  private void ensureNoRowBounds() {
    if (configuration.isSafeRowBoundsEnabled() && rowBounds != null && (rowBounds.getLimit() < RowBounds.NO_ROW_LIMIT || rowBounds.getOffset() > RowBounds.NO_ROW_OFFSET)) {
      throw new ExecutorException("Mapped Statements with nested result mappings cannot be safely constrained by RowBounds. "
          + "Use safeRowBoundsEnabled=false setting to bypass this check.");
    }
  }

  protected void checkResultHandler() {
    if (resultHandler != null && configuration.isSafeResultHandlerEnabled() && !mappedStatement.isResultOrdered()) {
      throw new ExecutorException("Mapped Statements with nested result mappings cannot be safely used with a custom ResultHandler. "
          + "Use safeResultHandlerEnabled=false setting to bypass this check "
          + "or ensure your statement returns ordered data and set resultOrdered=true on it.");
    }
  } 

  private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
      throws SQLException {
    DefaultResultContext resultContext = new DefaultResultContext();
    skipRows(rsw.getResultSet(), rowBounds);
    while (shouldProcessMoreRows(rsw.getResultSet(), resultContext, rowBounds)) {
      ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(rsw.getResultSet(), resultMap, null);
      Object rowValue = getRowValue(rsw, discriminatedResultMap);
      storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet());
    }
  }

  private void storeObject(ResultHandler resultHandler, DefaultResultContext resultContext, Object rowValue, ResultMapping parentMapping, ResultSet rs) throws SQLException {
    if (parentMapping != null) {
      linkToParent(rs, parentMapping, rowValue);
    } else {
      callResultHandler(resultHandler, resultContext, rowValue);
    }
  }

  private void callResultHandler(ResultHandler resultHandler, DefaultResultContext resultContext, Object rowValue) {
    resultContext.nextResultObject(rowValue);
    resultHandler.handleResult(resultContext);
  }

  private boolean shouldProcessMoreRows(ResultSet rs, ResultContext context, RowBounds rowBounds) throws SQLException {
    return !context.isStopped() && rs.next() && context.getResultCount() < rowBounds.getLimit();
  }

  private void skipRows(ResultSet rs, RowBounds rowBounds) throws SQLException {
    if (rs.getType() != ResultSet.TYPE_FORWARD_ONLY) {
      if (rowBounds.getOffset() != RowBounds.NO_ROW_OFFSET) {
        rs.absolute(rowBounds.getOffset());
      }
    } else {
      for (int i = 0; i < rowBounds.getOffset(); i++) {
        rs.next();
      }
    }
  }

  //
  // GET VALUE FROM ROW FOR SIMPLE RESULT MAP
  //

  private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap) throws SQLException {
    final ResultLoaderMap lazyLoader = new ResultLoaderMap();
    Object resultObject = createResultObject(rsw, resultMap, lazyLoader, null);
    if (resultObject != null && !typeHandlerRegistry.hasTypeHandler(resultMap.getType())) {
      final MetaObject metaObject = configuration.newMetaObject(resultObject);
      boolean foundValues = resultMap.getConstructorResultMappings().size() > 0;
      if (shouldApplyAutomaticMappings(resultMap, !AutoMappingBehavior.NONE.equals(configuration.getAutoMappingBehavior()))) {
        foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, null) || foundValues;
      }
      foundValues = applyPropertyMappings(resultObject,rsw, resultMap, metaObject, lazyLoader, null) || foundValues;
      foundValues = lazyLoader.size() > 0 || foundValues;
      resultObject = foundValues ? resultObject : null;
      return resultObject;
    }
    return resultObject;
  }

  private boolean shouldApplyAutomaticMappings(ResultMap resultMap, boolean def) {
    return resultMap.getAutoMapping() != null ? resultMap.getAutoMapping() : def;
  }

  //
  // PROPERTY MAPPINGS
  //

  private boolean applyPropertyMappings(Object resultObject,ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, ResultLoaderMap lazyLoader, String columnPrefix)
      throws SQLException {
    final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
    boolean foundValues = false;
    final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
    for (ResultMapping propertyMapping : propertyMappings) {
      final String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
      if (propertyMapping.isCompositeResult()
          || (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH)))
          || propertyMapping.getResultSet() != null) {
        Object value = getPropertyMappingValue(rsw.getResultSet(), metaObject, propertyMapping, lazyLoader, columnPrefix);
        //added by jerry
        if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) {
        	value = new dao.domain.Teacher();
        	try {
				value = propertyMapping.getJavaType().newInstance();
	        	value = configuration.getProxyFactory().createProxy(resultObject,propertyMapping.getProperty(),value, lazyLoader, configuration, objectFactory, new ArrayList(), new ArrayList());
			} catch (Exception e) {
				e.printStackTrace();
			}
        }

        final String property = propertyMapping.getProperty(); // issue #541 make property optional
        if (value != NO_VALUE && property != null && (value != null || configuration.isCallSettersOnNulls())) { // issue #377, call setter on nulls
          if (value != null || !metaObject.getSetterType(property).isPrimitive()) {
            metaObject.setValue(property, value);
          }
          foundValues = true;
        }
      }
    }

    return foundValues;
  }

  private Object getPropertyMappingValue(ResultSet rs, MetaObject metaResultObject, ResultMapping propertyMapping, ResultLoaderMap lazyLoader, String columnPrefix)
      throws SQLException {
    if (propertyMapping.getNestedQueryId() != null) {
      return getNestedQueryMappingValue(rs, metaResultObject, propertyMapping, lazyLoader, columnPrefix);
    } else if (propertyMapping.getResultSet() != null) {
      addPendingChildRelation(rs, metaResultObject, propertyMapping);
      return NO_VALUE;
    } else if (propertyMapping.getNestedResultMapId() != null) {
      // the user added a column attribute to a nested result map, ignore it
      return NO_VALUE;
    } else {
      final TypeHandler<?> typeHandler = propertyMapping.getTypeHandler();
      final String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
      return typeHandler.getResult(rs, column);
    }
  }

  private boolean applyAutomaticMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, String columnPrefix) throws SQLException {
    final List<String> unmappedColumnNames = rsw.getUnmappedColumnNames(resultMap, columnPrefix);
    boolean foundValues = false;
    for (String columnName : unmappedColumnNames) {
      String propertyName = columnName;
      if (columnPrefix != null && columnPrefix.length() > 0) {
        // When columnPrefix is specified,
        // ignore columns without the prefix.
        if (columnName.toUpperCase(Locale.ENGLISH).startsWith(columnPrefix)) {
          propertyName = columnName.substring(columnPrefix.length());
        } else {
          continue;
        }
      }
      final String property = metaObject.findProperty(propertyName, configuration.isMapUnderscoreToCamelCase());
      if (property != null && metaObject.hasSetter(property)) {
        final Class<?> propertyType = metaObject.getSetterType(property);
        if (typeHandlerRegistry.hasTypeHandler(propertyType)) {
          final TypeHandler<?> typeHandler = rsw.getTypeHandler(propertyType, columnName);
          final Object value = typeHandler.getResult(rsw.getResultSet(), columnName);
          if (value != null || configuration.isCallSettersOnNulls()) { // issue #377, call setter on nulls
            if (value != null || !propertyType.isPrimitive()) {
              metaObject.setValue(property, value);
            }
            foundValues = true;
          }
        }
      }
    }
    return foundValues;
  }

  // MULTIPLE RESULT SETS

  private void linkToParent(ResultSet rs, ResultMapping parentMapping, Object rowValue) throws SQLException {
    CacheKey parentKey = createKeyForMultipleResults(rs, parentMapping, parentMapping.getColumn(), parentMapping.getForeignColumn());
    PendingRelation parent = pendingRelations.get(parentKey);
    if (parent != null) {
      final Object collectionProperty = instantiateCollectionPropertyIfAppropriate(parent.propertyMapping, parent.metaObject);
      if (rowValue != null) {
        if (collectionProperty != null) {
          final MetaObject targetMetaObject = configuration.newMetaObject(collectionProperty);
          targetMetaObject.add(rowValue);
        } else {
          parent.metaObject.setValue(parent.propertyMapping.getProperty(), rowValue);
        }
      }
    }
  }

  private Object instantiateCollectionPropertyIfAppropriate(ResultMapping resultMapping, MetaObject metaObject) {
    final String propertyName = resultMapping.getProperty();
    Object propertyValue = metaObject.getValue(propertyName);
    if (propertyValue == null) {
      Class<?> type = resultMapping.getJavaType();
      if (type == null) {
        type = metaObject.getSetterType(propertyName);
      }
      try {
        if (objectFactory.isCollection(type)) {
          propertyValue = objectFactory.create(type);
          metaObject.setValue(propertyName, propertyValue);
          return propertyValue;
        }
      } catch (Exception e) {
        throw new ExecutorException("Error instantiating collection property for result '" + resultMapping.getProperty() + "'.  Cause: " + e, e);
      }
    } else if (objectFactory.isCollection(propertyValue.getClass())) {
      return propertyValue;
    }
    return null;
  }

  private void addPendingChildRelation(ResultSet rs, MetaObject metaResultObject, ResultMapping parentMapping) throws SQLException {
    CacheKey cacheKey = createKeyForMultipleResults(rs, parentMapping, parentMapping.getColumn(), parentMapping.getColumn());
    PendingRelation deferLoad = new PendingRelation();
    deferLoad.metaObject = metaResultObject;
    deferLoad.propertyMapping = parentMapping;
    pendingRelations.put(cacheKey, deferLoad);
    ResultMapping previous = nextResultMaps.get(parentMapping.getResultSet());
    if (previous == null) {
      nextResultMaps.put(parentMapping.getResultSet(), parentMapping);
    } else {
      if (!previous.equals(parentMapping)) {
        throw new ExecutorException("Two different properties are mapped to the same resultSet");
      }
    }
  }

  private CacheKey createKeyForMultipleResults(ResultSet rs, ResultMapping resultMapping, String names, String columns) throws SQLException {
    CacheKey cacheKey = new CacheKey();
    cacheKey.update(resultMapping);
    if (columns != null && names != null) {
      String[] columnsArray = columns.split(",");
      String[] namesArray = names.split(",");
      for (int i = 0 ; i < columnsArray.length ; i++) {
        Object value = rs.getString(columnsArray[i]);
        if (value != null) {
          cacheKey.update(namesArray[i]);
          cacheKey.update(value);
        }
      }
    }
    return cacheKey;
  }

  //
  // INSTANTIATION & CONSTRUCTOR MAPPING
  //

  private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, ResultLoaderMap lazyLoader, String columnPrefix) throws SQLException {
    final List<Class<?>> constructorArgTypes = new ArrayList<Class<?>>();
    final List<Object> constructorArgs = new ArrayList<Object>();
    final Object resultObject = createResultObject(rsw, resultMap, constructorArgTypes, constructorArgs, columnPrefix);
    //comment by jerry
//        if (resultObject != null && !typeHandlerRegistry.hasTypeHandler(resultMap.getType())) {
//      final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
//      for (ResultMapping propertyMapping : propertyMappings) {
//        if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) { // issue gcode #109 && issue #149
//          return configuration.getProxyFactory().createProxy(resultObject, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
//        }
//      }
//    }
    return resultObject;
  }

  private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, String columnPrefix)
      throws SQLException {
    final Class<?> resultType = resultMap.getType();
    final List<ResultMapping> constructorMappings = resultMap.getConstructorResultMappings();
    if (typeHandlerRegistry.hasTypeHandler(resultType)) {
      return createPrimitiveResultObject(rsw, resultMap, columnPrefix);
    } else if (constructorMappings.size() > 0) {
      return createParameterizedResultObject(rsw, resultType, constructorMappings, constructorArgTypes, constructorArgs, columnPrefix);
    } else {
      return objectFactory.create(resultType);
    }
  }

  private Object createParameterizedResultObject(ResultSetWrapper rsw, Class<?> resultType, List<ResultMapping> constructorMappings, List<Class<?>> constructorArgTypes,
      List<Object> constructorArgs, String columnPrefix) throws SQLException {
    boolean foundValues = false;
    for (ResultMapping constructorMapping : constructorMappings) {
      final Class<?> parameterType = constructorMapping.getJavaType();
      final String column = constructorMapping.getColumn();
      final Object value;
      if (constructorMapping.getNestedQueryId() != null) {
        value = getNestedQueryConstructorValue(rsw.getResultSet(), constructorMapping, columnPrefix);
      } else if (constructorMapping.getNestedResultMapId() != null) {
        final ResultMap resultMap = configuration.getResultMap(constructorMapping.getNestedResultMapId());
        value = getRowValue(rsw, resultMap);
      } else {
        final TypeHandler<?> typeHandler = constructorMapping.getTypeHandler();
        value = typeHandler.getResult(rsw.getResultSet(), prependPrefix(column, columnPrefix));
      }
      constructorArgTypes.add(parameterType);
      constructorArgs.add(value);
      foundValues = value != null || foundValues;
    }
    return foundValues ? objectFactory.create(resultType, constructorArgTypes, constructorArgs) : null;
  }

  private Object createPrimitiveResultObject(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {
    final Class<?> resultType = resultMap.getType();
    final String columnName;
    if (resultMap.getResultMappings().size() > 0) {
      final List<ResultMapping> resultMappingList = resultMap.getResultMappings();
      final ResultMapping mapping = resultMappingList.get(0);
      columnName = prependPrefix(mapping.getColumn(), columnPrefix);
    } else {
      columnName = rsw.getColumnNames().get(0);
    }
    final TypeHandler<?> typeHandler = rsw.getTypeHandler(resultType, columnName);
    return typeHandler.getResult(rsw.getResultSet(), columnName);
  }

  //
  // NESTED QUERY
  //

  private Object getNestedQueryConstructorValue(ResultSet rs, ResultMapping constructorMapping, String columnPrefix) throws SQLException {
    final String nestedQueryId = constructorMapping.getNestedQueryId();
    final MappedStatement nestedQuery = configuration.getMappedStatement(nestedQueryId);
    final Class<?> nestedQueryParameterType = nestedQuery.getParameterMap().getType();
    final Object nestedQueryParameterObject = prepareParameterForNestedQuery(rs, constructorMapping, nestedQueryParameterType, columnPrefix);
    Object value = null;
    if (nestedQueryParameterObject != null) {
      final BoundSql nestedBoundSql = nestedQuery.getBoundSql(nestedQueryParameterObject);
      final CacheKey key = executor.createCacheKey(nestedQuery, nestedQueryParameterObject, RowBounds.DEFAULT, nestedBoundSql);
      final Class<?> targetType = constructorMapping.getJavaType();
      final ResultLoader resultLoader = new ResultLoader(configuration, executor, nestedQuery, nestedQueryParameterObject, targetType, key, nestedBoundSql);
      value = resultLoader.loadResult();
    }
    return value;
  }

  private Object getNestedQueryMappingValue(ResultSet rs, MetaObject metaResultObject, ResultMapping propertyMapping, ResultLoaderMap lazyLoader, String columnPrefix)
      throws SQLException {
    final String nestedQueryId = propertyMapping.getNestedQueryId();
    final String property = propertyMapping.getProperty();
    final MappedStatement nestedQuery = configuration.getMappedStatement(nestedQueryId);
    final Class<?> nestedQueryParameterType = nestedQuery.getParameterMap().getType();
    final Object nestedQueryParameterObject = prepareParameterForNestedQuery(rs, propertyMapping, nestedQueryParameterType, columnPrefix);
    Object value = NO_VALUE;
    if (nestedQueryParameterObject != null) {
      final BoundSql nestedBoundSql = nestedQuery.getBoundSql(nestedQueryParameterObject);
      final CacheKey key = executor.createCacheKey(nestedQuery, nestedQueryParameterObject, RowBounds.DEFAULT, nestedBoundSql);
      final Class<?> targetType = propertyMapping.getJavaType();
      if (executor.isCached(nestedQuery, key)) {
        executor.deferLoad(nestedQuery, metaResultObject, property, key, targetType);
      } else {
        final ResultLoader resultLoader = new ResultLoader(configuration, executor, nestedQuery, nestedQueryParameterObject, targetType, key, nestedBoundSql);
        if (propertyMapping.isLazy()) {
          lazyLoader.addLoader(property, metaResultObject, resultLoader);
        } else {
          value = resultLoader.loadResult();
        }
      }
    }
    return value;
  }

  private Object prepareParameterForNestedQuery(ResultSet rs, ResultMapping resultMapping, Class<?> parameterType, String columnPrefix) throws SQLException {
    if (resultMapping.isCompositeResult()) {
      return prepareCompositeKeyParameter(rs, resultMapping, parameterType, columnPrefix);
    } else {
      return prepareSimpleKeyParameter(rs, resultMapping, parameterType, columnPrefix);
    }
  }

  private Object prepareSimpleKeyParameter(ResultSet rs, ResultMapping resultMapping, Class<?> parameterType, String columnPrefix) throws SQLException {
    final TypeHandler<?> typeHandler;
    if (typeHandlerRegistry.hasTypeHandler(parameterType)) {
      typeHandler = typeHandlerRegistry.getTypeHandler(parameterType);
    } else {
      typeHandler = typeHandlerRegistry.getUnknownTypeHandler();
    }
    return typeHandler.getResult(rs, prependPrefix(resultMapping.getColumn(), columnPrefix));
  }

  private Object prepareCompositeKeyParameter(ResultSet rs, ResultMapping resultMapping, Class<?> parameterType, String columnPrefix) throws SQLException {
    final Object parameterObject = instantiateParameterObject(parameterType);
    final MetaObject metaObject = configuration.newMetaObject(parameterObject);
    boolean foundValues = false;
    for (ResultMapping innerResultMapping : resultMapping.getComposites()) {
      final Class<?> propType = metaObject.getSetterType(innerResultMapping.getProperty());
      final TypeHandler<?> typeHandler = typeHandlerRegistry.getTypeHandler(propType);
      final Object propValue = typeHandler.getResult(rs, prependPrefix(innerResultMapping.getColumn(), columnPrefix));
      if (propValue != null) { // issue #353 & #560 do not execute nested query if key is null
        metaObject.setValue(innerResultMapping.getProperty(), propValue);
        foundValues = true;
      }
    }
    return foundValues ? parameterObject : null;
  }

  private Object instantiateParameterObject(Class<?> parameterType) {
    if (parameterType == null) {
      return new HashMap<Object, Object>();
    } else {
      return objectFactory.create(parameterType);
    }
  }

  //
  // DISCRIMINATOR
  //

  public ResultMap resolveDiscriminatedResultMap(ResultSet rs, ResultMap resultMap, String columnPrefix) throws SQLException {
    Set<String> pastDiscriminators = new HashSet<String>();
    Discriminator discriminator = resultMap.getDiscriminator();
    while (discriminator != null) {
      final Object value = getDiscriminatorValue(rs, discriminator, columnPrefix);
      final String discriminatedMapId = discriminator.getMapIdFor(String.valueOf(value));
      if (configuration.hasResultMap(discriminatedMapId)) {
        resultMap = configuration.getResultMap(discriminatedMapId);
        Discriminator lastDiscriminator = discriminator;
        discriminator = resultMap.getDiscriminator();
        if (discriminator == lastDiscriminator || !pastDiscriminators.add(discriminatedMapId)) {
          break;
        }
      } else {
        break;
      }
    }
    return resultMap;
  }

  private Object getDiscriminatorValue(ResultSet rs, Discriminator discriminator, String columnPrefix) throws SQLException {
    final ResultMapping resultMapping = discriminator.getResultMapping();
    final TypeHandler<?> typeHandler = resultMapping.getTypeHandler();
    return typeHandler.getResult(rs, prependPrefix(resultMapping.getColumn(), columnPrefix));
  }

  private String prependPrefix(String columnName, String prefix) {
    if (columnName == null || columnName.length() == 0 || prefix == null || prefix.length() == 0) {
      return columnName;
    }
    return prefix + columnName;
  }

  //
  // HANDLE NESTED RESULT MAPS
  //

  private void handleRowValuesForNestedResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
    final DefaultResultContext resultContext = new DefaultResultContext();
    skipRows(rsw.getResultSet(), rowBounds);
    Object rowValue = null;
    while (shouldProcessMoreRows(rsw.getResultSet(), resultContext, rowBounds)) {
      final ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(rsw.getResultSet(), resultMap, null);
      final CacheKey rowKey = createRowKey(discriminatedResultMap, rsw, null);
      Object partialObject = nestedResultObjects.get(rowKey);
      if (mappedStatement.isResultOrdered()) { // issue #577 && #542
        if (partialObject == null && rowValue != null) {
          nestedResultObjects.clear();
          storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet());
        }
        rowValue = getRowValue(rsw, discriminatedResultMap, rowKey, rowKey, null, partialObject);
      } else {
        rowValue = getRowValue(rsw, discriminatedResultMap, rowKey, rowKey, null, partialObject);
        if (partialObject == null) {
          storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet());
        }
      }
    }
    if (rowValue != null && mappedStatement.isResultOrdered()) {
      storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet());
    }
  }

  //
  // GET VALUE FROM ROW FOR NESTED RESULT MAP
  //

  private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, CacheKey combinedKey, CacheKey absoluteKey, String columnPrefix, Object partialObject) throws SQLException {
    final String resultMapId = resultMap.getId();
    Object resultObject = partialObject;
    if (resultObject != null) {
      final MetaObject metaObject = configuration.newMetaObject(resultObject);
      putAncestor(absoluteKey, resultObject, resultMapId, columnPrefix);
      applyNestedResultMappings(rsw, resultMap, metaObject, columnPrefix, combinedKey, false);
      ancestorObjects.remove(absoluteKey);
    } else {
      final ResultLoaderMap lazyLoader = new ResultLoaderMap();
      resultObject = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);
      if (resultObject != null && !typeHandlerRegistry.hasTypeHandler(resultMap.getType())) {
        final MetaObject metaObject = configuration.newMetaObject(resultObject);
        boolean foundValues = resultMap.getConstructorResultMappings().size() > 0;
        if (shouldApplyAutomaticMappings(resultMap, AutoMappingBehavior.FULL.equals(configuration.getAutoMappingBehavior()))) {
          foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;
        }
        foundValues = applyPropertyMappings(resultObject,rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;
        putAncestor(absoluteKey, resultObject, resultMapId, columnPrefix);
        foundValues = applyNestedResultMappings(rsw, resultMap, metaObject, columnPrefix, combinedKey, true) || foundValues;
        ancestorObjects.remove(absoluteKey);
        foundValues = lazyLoader.size() > 0 || foundValues;
        resultObject = foundValues ? resultObject : null;
      }
      if (combinedKey != CacheKey.NULL_CACHE_KEY) nestedResultObjects.put(combinedKey, resultObject);
    }
    return resultObject;
  }

  private void putAncestor(CacheKey rowKey, Object resultObject, String resultMapId, String columnPrefix) {
    if (!ancestorColumnPrefix.containsKey(resultMapId)) {
      ancestorColumnPrefix.put(resultMapId, columnPrefix);
    }
    ancestorObjects.put(rowKey, resultObject);
  }

  //
  // NESTED RESULT MAP (JOIN MAPPING)
  //

  private boolean applyNestedResultMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, String parentPrefix, CacheKey parentRowKey, boolean newObject) {
    boolean foundValues = false;
    for (ResultMapping resultMapping : resultMap.getPropertyResultMappings()) {
      final String nestedResultMapId = resultMapping.getNestedResultMapId();
      if (nestedResultMapId != null && resultMapping.getResultSet() == null) {
        try {
          final String columnPrefix = getColumnPrefix(parentPrefix, resultMapping);
          final ResultMap nestedResultMap = getNestedResultMap(rsw.getResultSet(), nestedResultMapId, columnPrefix);
          CacheKey rowKey = null;
          Object ancestorObject = null;
          if (ancestorColumnPrefix.containsKey(nestedResultMapId)) {
            rowKey = createRowKey(nestedResultMap, rsw, ancestorColumnPrefix.get(nestedResultMapId));
            ancestorObject = ancestorObjects.get(rowKey);
          }
          if (ancestorObject != null) {
            if (newObject) metaObject.setValue(resultMapping.getProperty(), ancestorObject);
          } else {
            rowKey = createRowKey(nestedResultMap, rsw, columnPrefix);
            final CacheKey combinedKey = combineKeys(rowKey, parentRowKey);
            Object rowValue = nestedResultObjects.get(combinedKey);
            boolean knownValue = (rowValue != null);
            final Object collectionProperty = instantiateCollectionPropertyIfAppropriate(resultMapping, metaObject);
            if (anyNotNullColumnHasValue(resultMapping, columnPrefix, rsw.getResultSet())) {
              rowValue = getRowValue(rsw, nestedResultMap, combinedKey, rowKey, columnPrefix, rowValue);
              if (rowValue != null && !knownValue) {
                if (collectionProperty != null) {
                  final MetaObject targetMetaObject = configuration.newMetaObject(collectionProperty);
                  targetMetaObject.add(rowValue);
                } else {
                  metaObject.setValue(resultMapping.getProperty(), rowValue);
                }
                foundValues = true;
              }
            }
          }
        } catch (SQLException e) {
          throw new ExecutorException("Error getting nested result map values for '" + resultMapping.getProperty() + "'.  Cause: " + e, e);
        }
      }
    }
    return foundValues;
  }

  private String getColumnPrefix(String parentPrefix, ResultMapping resultMapping) {
    final StringBuilder columnPrefixBuilder = new StringBuilder();
    if (parentPrefix != null) columnPrefixBuilder.append(parentPrefix);
    if (resultMapping.getColumnPrefix() != null) columnPrefixBuilder.append(resultMapping.getColumnPrefix());
    final String columnPrefix = columnPrefixBuilder.length() == 0 ? null : columnPrefixBuilder.toString().toUpperCase(Locale.ENGLISH);
    return columnPrefix;
  }

  private boolean anyNotNullColumnHasValue(ResultMapping resultMapping, String columnPrefix, ResultSet rs) throws SQLException {
    Set<String> notNullColumns = resultMapping.getNotNullColumns();
    boolean anyNotNullColumnHasValue = true;
    if (notNullColumns != null && !notNullColumns.isEmpty()) {
      anyNotNullColumnHasValue = false;
      for (String column: notNullColumns) {
        rs.getObject(prependPrefix(column, columnPrefix));
        if (!rs.wasNull()) {
          anyNotNullColumnHasValue = true;
          break;
        }
      }
    }
    return anyNotNullColumnHasValue;
  }

  private ResultMap getNestedResultMap(ResultSet rs, String nestedResultMapId, String columnPrefix) throws SQLException {
    ResultMap nestedResultMap = configuration.getResultMap(nestedResultMapId);
    nestedResultMap = resolveDiscriminatedResultMap(rs, nestedResultMap, columnPrefix);
    return nestedResultMap;
  }

  //
  // UNIQUE RESULT KEY
  //

  private CacheKey createRowKey(ResultMap resultMap, ResultSetWrapper rsw, String columnPrefix) throws SQLException {
    final CacheKey cacheKey = new CacheKey();
    cacheKey.update(resultMap.getId());
    List<ResultMapping> resultMappings = getResultMappingsForRowKey(resultMap);
    if (resultMappings.size() == 0) {
      if (Map.class.isAssignableFrom(resultMap.getType())) {
        createRowKeyForMap(rsw, cacheKey);
      } else {
        createRowKeyForUnmappedProperties(resultMap, rsw, cacheKey, columnPrefix);
      }
    } else {
      createRowKeyForMappedProperties(resultMap, rsw, cacheKey, resultMappings, columnPrefix);
    }
    return cacheKey;
  }

  private CacheKey combineKeys(CacheKey rowKey, CacheKey parentRowKey) {
    if (rowKey.getUpdateCount() > 1 && parentRowKey.getUpdateCount() > 1) {
      CacheKey combinedKey;
      try {
        combinedKey = rowKey.clone();
      } catch (CloneNotSupportedException e) {
        throw new ExecutorException("Error cloning cache key.  Cause: " + e, e);
      }
      combinedKey.update(parentRowKey);
      return combinedKey;
    }
    return CacheKey.NULL_CACHE_KEY;
  }

  private List<ResultMapping> getResultMappingsForRowKey(ResultMap resultMap) {
    List<ResultMapping> resultMappings = resultMap.getIdResultMappings();
    if (resultMappings.size() == 0) {
      resultMappings = resultMap.getPropertyResultMappings();
    }
    return resultMappings;
  }

  private void createRowKeyForMappedProperties(ResultMap resultMap, ResultSetWrapper rsw, CacheKey cacheKey, List<ResultMapping> resultMappings, String columnPrefix) throws SQLException {
    for (ResultMapping resultMapping : resultMappings) {
      if (resultMapping.getNestedResultMapId() != null && resultMapping.getResultSet() == null) { // Issue #392
        final ResultMap nestedResultMap = configuration.getResultMap(resultMapping.getNestedResultMapId());
        createRowKeyForMappedProperties(nestedResultMap, rsw, cacheKey, nestedResultMap.getConstructorResultMappings(),
            prependPrefix(resultMapping.getColumnPrefix(), columnPrefix));
      } else if (resultMapping.getNestedQueryId() == null) {
        final String column = prependPrefix(resultMapping.getColumn(), columnPrefix);
        final TypeHandler<?> th = resultMapping.getTypeHandler();
        List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
        if (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH))) { // Issue #114
          final Object value = th.getResult(rsw.getResultSet(), column);
          if (value != null) {
            cacheKey.update(column);
            cacheKey.update(value);
          }
        }
      }
    }
  }

  private void createRowKeyForUnmappedProperties(ResultMap resultMap, ResultSetWrapper rsw, CacheKey cacheKey, String columnPrefix) throws SQLException {
    final MetaClass metaType = MetaClass.forClass(resultMap.getType());
    List<String> unmappedColumnNames = rsw.getUnmappedColumnNames(resultMap, columnPrefix);
    for (String column : unmappedColumnNames) {
      String property = column;
      if (columnPrefix != null && columnPrefix.length() > 0) {
        // When columnPrefix is specified,
        // ignore columns without the prefix.
        if (column.toUpperCase(Locale.ENGLISH).startsWith(columnPrefix)) {
          property = column.substring(columnPrefix.length());
        } else {
          continue;
        }
      }
      if (metaType.findProperty(property, configuration.isMapUnderscoreToCamelCase()) != null) {
        String value = rsw.getResultSet().getString(column);
        if (value != null) {
          cacheKey.update(column);
          cacheKey.update(value);
        }
      }
    }
  }

  private void createRowKeyForMap(ResultSetWrapper rsw, CacheKey cacheKey) throws SQLException {
    List<String> columnNames = rsw.getColumnNames();
    for (String columnName : columnNames) {
      final String value = rsw.getResultSet().getString(columnName);
      if (value != null) {
        cacheKey.update(columnName);
        cacheKey.update(value);
      }
    }
  }

}