mybatis工作原理及流程 mybatis延迟加载原理( 二 ) _云知道

延迟加载代理对象创建
DefaultResultSetHandler
//#mark 创建结果对象 private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, ResultLoaderMap lazyLoader, String columnPrefix) throws SQLException { this.useConstructorMappings = false; // reset previous mapping result final List<Class<?>> constructorArgTypes = new ArrayList<Class<?>>(); final List<Object> constructorArgs = new ArrayList<Object>(); //#mark 创建返回的结果映射的真实对象 Object resultObject = createResultObject(rsw, resultMap, constructorArgTypes, constructorArgs, columnPrefix); if (resultObject != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) { final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings(); for (ResultMapping propertyMapping : propertyMappings) { // issue gcode #109 && issue #149 判断属性有没配置嵌套查询，如果有就创建代理对象 if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) { //#mark 创建延迟加载代理对象 resultObject = configuration.getProxyFactory().createProxy(resultObject, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs); break; } } } this.useConstructorMappings = resultObject != null && !constructorArgTypes.isEmpty(); // set current mapping result return resultObject; }代理功能实现

【mybatis工作原理及流程 mybatis延迟加载原理】由于Javasisst和Cglib的代理实现基本相同，这里主要介绍Javasisst

ProxyFactory接口定义
public interface ProxyFactory {
void setProperties(Properties properties);
/**
* 创建代理
* @param target 目标结果对象
* @param lazyLoader 延迟加载对象
* @param configuration 配置
* @param objectFactory 对象工厂
* @param constructorArgTypes 构造参数类型
* @param constructorArgs 构造参数值
* @return
*/
Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs);
}
JavasisstProxyFactory实现
public class JavassistProxyFactory implements org.apache.ibatis.executor.loader.ProxyFactory {/** * 接口实现 * @param target 目标结果对象 * @param lazyLoader 延迟加载对象 * @param configuration 配置 * @param objectFactory 对象工厂 * @param constructorArgTypes 构造参数类型 * @param constructorArgs 构造参数值 * @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.../** * 代理对象实现，核心逻辑执行 */ private static class EnhancedResultObjectProxyImpl implements MethodHandler {/** * 创建代理对象 * @param type * @param callback * @param constructorArgTypes * @param constructorArgs * @return */ static Object crateProxy(Class<?> type, MethodHandler callback, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) { ProxyFactory enhancer = new ProxyFactory(); enhancer.setSuperclass(type); try { //通过获取对象方法，判断是否存在该方法 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) { //没找到该方法，实现接口 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 { //创建新的代理对象 enhanced = enhancer.create(typesArray, valuesArray); } catch (Exception e) { throw new ExecutorException("Error creating lazy proxy. Cause: " + e, e); } //设置代理执行器 ((Proxy) enhanced).setHandler(callback); return enhanced; }/** * 代理对象执行 * @param enhanced 原对象 * @param method 原对象方法 * @param methodProxy 代理方法 * @param args 方法参数 * @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)) {//忽略暂未找到具体作用 Object original; 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 { //延迟加载数量大于0 if (lazyLoader.size() > 0 && !FINALIZE_METHOD.equals(methodName)) { //aggressive 一次加载性所有需要要延迟加载属性或者包含触发延迟加载方法 if (aggressive || lazyLoadTriggerMethods.contains(methodName)) { log.debug("==> laze lod trigger method:" + methodName + ",proxy method:" + methodProxy.getName() + " class:" + enhanced.getClass()); //一次全部加载 lazyLoader.loadAll(); } else if (PropertyNamer.isSetter(methodName)) { //判断是否为set方法， set方法不需要延迟加载 final String property = PropertyNamer.methodToProperty(methodName); lazyLoader.remove(property); } else if (PropertyNamer.isGetter(methodName)) { final String property = PropertyNamer.methodToProperty(methodName); if (lazyLoader.hasLoader(property)) { //延迟加载单个属性 lazyLoader.load(property); log.debug("load one :" + methodName); } } } } } return methodProxy.invoke(enhanced, args); } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } } }