因为通过javassist和cglib代理实现的，所以说到底最主要的就是JavasisstProxyFactory类中的invoke方法和里面的load方法。
其实读一读，里面的逻辑就是跟配置中定义的规则一样的
因为github上的mybatis中文版中这部分注释比较少，所以从网上寻找博客，截取了代码注释片段记录下。
JavasisstProxyFactory
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);
}
}
}
load方法
/**
* 执行懒加载查询，获取数据并且set到userObject中返回
* @param userObject
* @throws SQLException
*/
public void load(final Object userObject) throws SQLException {
//合法性校验
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.");
}
//获取mappedstatement并且校验
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构建metaobject,并且重新构建resultloader对象
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, new ClosedExecutor(), old.mappedStatement,
old.parameterObject, old.targetType, old.cacheKey, old.boundSql);
}
//获取数据库查询结果并且set到结果对象返回
this.metaResultObject.setValue(property, this.resultLoader.loadResult());
}
参考地址：
https://www.cnblogs.com/qixidi/p/10251126.html
https://blog.csdn.net/mingtian625/article/details/47358003
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