因為通過javassist和cglib代理實現的，所以說到底最主要的就是JavasisstProxyFactory類中的invoke方法和裡面的load方法。

其實讀一讀，裡面的邏輯就是跟配置中定義的規則一樣的
因為github上的mybatis中文版中這部分註釋比較少，所以從網上尋找部落格，截取了程式碼註釋片段記錄下。
JavasisstProxyFactory

public class JavassistProxyFactory implements org.apache.ibatis.executor.loader.ProxyFactory {

 
 /**
 * 介面實現
 * @param target 目標結果物件
 * @param lazyLoader 延遲載入物件
 * @param configuration 配置
 * @param objectFactory 物件工廠
 * @param constructorArgTypes 構造引數型別
 * @param constructorArgs 構造引數值
 * @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);
 }

 //省略...
 
 /**
 * 代理物件實現，核心邏輯執行
 */
 private static class EnhancedResultObjectProxyImpl implements MethodHandler {
 
 /**
 * 建立代理物件
 * @param type
 * @param callback
 * @param constructorArgTypes
 * @param constructorArgs
 * @return
 */
 static Object crateProxy(Class<?> type,MethodHandler callback,List<Object> constructorArgs) {

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

 try {
  //通過獲取物件方法，判斷是否存在該方法
  type.getDeclaredMethod(WRITE_REPLACE_METHOD);
  // ObjectOutputStream will call writeReplace of objects returned by writeReplace
  if (log.isDebugEnabled()) {
  log.debug(WRITE_REPLACE_METHOD + " method was found on bean " + type + ",make sure it returns this");
  }
 } catch (NoSuchMethodException e) {
  //沒找到該方法，實現介面
  enhancer.setInterfaces(new Class[]{WriteReplaceInterface.class});
 } catch (SecurityException e) {
  // nothing to do here
 }

 Object enhanced;
 Class<?>[] typesArray = constructorArgTypes.toArray(new Class[constructorArgTypes.size()]);
 Object[] valuesArray = constructorArgs.toArray(new Object[constructorArgs.size()]);
 try {
  //建立新的代理物件
  enhanced = enhancer.create(typesArray,valuesArray);
 } catch (Exception e) {
  throw new ExecutorException("Error creating lazy proxy. Cause: " + e,e);
 }
 //設定代理執行器
 ((Proxy) enhanced).setHandler(callback);
 return enhanced;
 }
 
 
  /**
  * 代理物件執行
  * @param enhanced 原物件
  * @param method 原物件方法
  * @param methodProxy 代理方法
  * @param args 方法引數
  * @return
  * @throws Throwable
  */
 @Override
 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)) { 
   //忽略暫未找到具體作用
   Object original;
   if (constructorArgTypes.isEmpty()) {
    original = objectFactory.create(type);
   } else {
    original = objectFactory.create(type,constructorArgs);
   }
   PropertyCopier.copyBeanProperties(type,enhanced,original);
   if (lazyLoader.size() > 0) {
    return new JavassistSerialStateHolder(original,lazyLoader.getProperties(),constructorArgs);
   } else {
    return original;
   }
   } else {
    //延遲載入數量大於0
   if (lazyLoader.size() > 0 && !FINALIZE_METHOD.equals(methodName)) {
    //aggressive 一次載入性所有需要要延遲載入屬性或者包含觸發延遲載入方法
    if (aggressive || lazyLoadTriggerMethods.contains(methodName)) {
    log.debug("==> laze lod trigger method:" + methodName + ",proxy method:" + methodProxy.getName() + " class:" + enhanced.getClass());
    //一次全部載入
    lazyLoader.loadAll();
    } else if (PropertyNamer.isSetter(methodName)) {
    //判斷是否為set方法，set方法不需要延遲載入
    final String property = PropertyNamer.methodToProperty(methodName);
    lazyLoader.remove(property);
    } else if (PropertyNamer.isGetter(methodName)) {
    final String property = PropertyNamer.methodToProperty(methodName);
    if (lazyLoader.hasLoader(property)) {
     //延遲載入單個屬性
     lazyLoader.load(property);
     log.debug("load one :" + methodName);
    }
    }
   }
   }
  }
  return methodProxy.invoke(enhanced,args);
  } catch (Throwable t) {
  throw ExceptionUtil.unwrapThrowable(t);
  }
 }
 }

load方法

/**
  * 執行懶載入查詢，獲取資料並且set到userObject中返回
  * @param userObject
  * @throws SQLException
  */
 public void load(final Object userObject) throws SQLException {
  
  //合法性校驗
  if (this.metaResultObject == null || this.resultLoader == null) {
  if (this.mappedParameter == null) {
   throw new ExecutorException("Property [" + this.property + "] cannot be loaded because "
     + "required parameter of mapped statement ["
     + this.mappedStatement + "] is not serializable.");
  }
  
  //獲取mappedstatement並且校驗
  final Configuration config = this.getConfiguration();
  final MappedStatement ms = config.getMappedStatement(this.mappedStatement);
  if (ms == null) {
   throw new ExecutorException("Cannot lazy load property [" + this.property
     + "] of deserialized object [" + userObject.getClass()
     + "] because configuration does not contain statement ["
     + this.mappedStatement + "]");
  }
 
  //使用userObject構建metaobject,並且重新構建resultloader物件
  this.metaResultObject = config.newMetaObject(userObject);
  this.resultLoader = new ResultLoader(config,new ClosedExecutor(),ms,this.mappedParameter,metaResultObject.getSetterType(this.property),null,null);
  }
 
  /* We are using a new executor because we may be (and likely are) on a new thread
  * and executors aren't thread safe. (Is this sufficient?)
  *
  * A better approach would be making executors thread safe. */
  if (this.serializationCheck == null) {
  final ResultLoader old = this.resultLoader;
  this.resultLoader = new ResultLoader(old.configuration,old.mappedStatement,old.parameterObject,old.targetType,old.cacheKey,old.boundSql);
  }
 
  //獲取資料庫查詢結果並且set到結果物件返回
  this.metaResultObject.setValue(property,this.resultLoader.loadResult());
 }

參考地址：
https://www.cnblogs.com/qixidi/p/10251126.html
https://blog.csdn.net/mingtian625/article/details/47358003

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