ProxyFactory是创建代理类的工厂接口，其中的setProperties方法用来对工厂进行属性设置，但是mybatis内置的两个实现类都没有实现该接口，所以不支持属性设置。createProxy方法用来创建一个代理对象
public interface ProxyFactory {
// 设置工厂属性
default void setProperties(Properties properties) {
}
// 创建代理对象
Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs);
}ProxyFactory接口有2个实现类，CglibProxyFactory和JavassistProxyFactor类。这两个实现类整体结构高度一致，内部类、方法设置都一样，只是实现原理不同。CglibProxyFactory基于cglib实现，JavassistProxyFactor基于javassist实现。
接下来以CglibProxyFactory类为源码进行分析：
CglibProxyFactory类中提供了两个创建代理对象的方法。其中createProxy方法重写了一个普通的代理对象，createDeserializationProxy方法用来创建一个反序列化的代理对象。
public class CglibProxyFactory implements ProxyFactory {
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);
}
}
// 创建一个代理
@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);
}
// 创建一个反序列化的代理
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);
}
private static class EnhancedResultObjectProxyImpl implements MethodInterceptor {
// 被代理类
private final Class<?> type;
// 要懒加载的属性Map
private final ResultLoaderMap lazyLoader;
// 是否是激进懒加载
private final boolean aggressive;
// 能够触发懒加载的方法名“equals”, “clone”, “hashCode”, “toString”。这四个方法名在Configuration中被初始化。
private final Set<String> lazyLoadTriggerMethods;
// 对象工厂
private final ObjectFactory objectFactory;
// 被代理类构造函数的参数类型列表
private final List<Class<?>> constructorArgTypes;
// 被代理类构造函数的参数列表
private final List<Object> constructorArgs;
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;
}
public static Object createProxy(Object target, ResultLoaderMap lazyLoader, Configuration configuration, ObjectFactory objectFactory, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {
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;
}
@Override
public Object intercept(Object enhanced, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
// 取出被代理类中此次被调用的方法的名称
final String methodName = method.getName();
try {
synchronized (lazyLoader) { // 防止属性的并发加载
if (WRITE_REPLACE_METHOD.equals(methodName)) { // 被调用的是writeReplace方法
// 创建一个原始对象
Object original;
if (constructorArgTypes.isEmpty()) {
original = objectFactory.create(type);
} else {
original = objectFactory.create(type, constructorArgTypes, constructorArgs);
}
// 将被代理对象的属性拷贝进入新创建的对象
PropertyCopier.copyBeanProperties(type, enhanced, original);
if (lazyLoader.size() > 0) { // 存在懒加载属性
// 则此时返回的信息要更多，不仅仅是原对象，还有相关的懒加载的设置等信息。因此使用CglibSerialStateHolder进行一次封装
return new CglibSerialStateHolder(original, lazyLoader.getProperties(), objectFactory, constructorArgTypes, constructorArgs);
} else {
// 没有未懒加载的属性了，那直接返回原对象进行序列化
return original;
}
} else {
if (lazyLoader.size() > 0 && !FINALIZE_METHOD.equals(methodName)) { // 存在懒加载属性且被调用的不是finalize方法
if (aggressive || lazyLoadTriggerMethods.contains(methodName)) { // 设置了激进懒加载或者被调用的方法是能够触发全局懒加载的方法
// 完成所有属性的懒加载
lazyLoader.loadAll();
} else if (PropertyNamer.isSetter(methodName)) { // 调用了属性写方法
// 则先清除该属性的懒加载设置。该属性不需要被懒加载了
final String property = PropertyNamer.methodToProperty(methodName);
lazyLoader.remove(property);
} else if (PropertyNamer.isGetter(methodName)) { // 调用了属性读方法
final String property = PropertyNamer.methodToProperty(methodName);
// 如果该属性是尚未加载的懒加载属性，则进行懒加载
if (lazyLoader.hasLoader(property)) {
lazyLoader.load(property);
}
}
}
}
}
// 触发被代理类的相应方法。能够进行到这里的是除去writeReplace方法外的方法，例如读写方法、toString方法等
return methodProxy.invokeSuper(enhanced, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
}
}代理类最核心的方法是intercept方法,当被代理对象的其他方法被调用时，intercept方法的处理方式是：
如果设置了激进懒加载或者被调用的是触发全局加载的方法，则直接加载所有未加载的属性。
如果被调用的是属性写方法，则将该方法从懒加载列表中删除，因为此时数据库中的数据已经不是最新的，没有必要再去加载，然后进行属性的写入操作。
如果被调用的是读方法，则该属性尚未被懒加载的情况下，则加载该属性，如果该属性已经被懒加载过，则直接读取该属性。
ResultLoaderMap类：
被代理对象可能会有多个属性可以被懒加载，这些尚未完成加载的属性是在ResultLoaderMap类的实例中存储的。ResultLoaderMap类主要就是一个map类，该类key为属性名的大写，value为LoadPair对象。LoadPair类是ResultLoaderMap类的内部类，它能实现对应属性的懒加载功能。
public static class LoadPair implements Serializable {
private static final long serialVersionUID = 20130412;
// 用来根据反射得到数据库连接的方法名
private static final String FACTORY_METHOD = "getConfiguration";
// 判断是否经过了序列化的标志位，因为该属性被设置了transient，经过一次序列化和反序列化后会变为null
private final transient Object serializationCheck = new Object();
// 输出结果对象的封装
private transient MetaObject metaResultObject;
// 用以加载未加载属性的加载器
private transient ResultLoader resultLoader;
// 日志记录器
private transient Log log;
// 用来获取数据库连接的工厂
private Class<?> configurationFactory;
// 未加载的属性的属性名
private String property;
// 能够加载未加载属性的SQL的编号
private String mappedStatement;
// 能够加载未加载属性的SQL的参数
private Serializable mappedParameter;
private LoadPair(final String property, MetaObject metaResultObject, ResultLoader resultLoader) {
this.property = property;
this.metaResultObject = metaResultObject;
this.resultLoader = resultLoader;
if (metaResultObject != null && metaResultObject.getOriginalObject() instanceof Serializable) {
final Object mappedStatementParameter = resultLoader.parameterObject;
if (mappedStatementParameter instanceof Serializable) {
this.mappedStatement = resultLoader.mappedStatement.getId();
this.mappedParameter = (Serializable) mappedStatementParameter;
this.configurationFactory = resultLoader.configuration.getConfigurationFactory();
} else {
Log log = this.getLogger();
if (log.isDebugEnabled()) {
log.debug("Property [" + this.property + "] of ["
+ metaResultObject.getOriginalObject().getClass() + "] cannot be loaded "
+ "after deserialization. Make sure it's loaded before serializing "
+ "forenamed object.");
}
}
}
}
public void load() throws SQLException {
if (this.metaResultObject == null) {
throw new IllegalArgumentException("metaResultObject is null");
}
if (this.resultLoader == null) {
throw new IllegalArgumentException("resultLoader is null");
}
this.load(null);
}
public void load(final Object userObject) throws SQLException {
if (this.metaResultObject == null || this.resultLoader == null) { // 输出结果对象的封装不存在或者输出结果加载器不存在
// 判断用以加载属性的对应的SQL语句存在
if (this.mappedParameter == null) {
throw new ExecutorException("Property [" + this.property + "] cannot be loaded because "
+ "required parameter of mapped statement ["
+ this.mappedStatement + "] is not serializable.");
}
final Configuration config = this.getConfiguration();
// 取出用来加载结果的SQL语句
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 + "]");
}
// 创建结果对象的包装
this.metaResultObject = config.newMetaObject(userObject);
// 创建结果加载器
this.resultLoader = new ResultLoader(config, new ClosedExecutor(), ms, this.mappedParameter,
metaResultObject.getSetterType(this.property), null, null);
}
// 只要经历过持久化，则可能在别的线程中了。为这次惰性加载创建的新线程ResultLoader
if (this.serializationCheck == null) {
// 取出原来的ResultLoader中的必要信息，然后创建一个新的
// 这是因为load函数可能在不同的时间多次执行（第一次加载属性A，又过了好久加载属性B）。
// 而该对象的各种属性是跟随对象的，加载属性B时还保留着加载属性A时的状态，即ResultLoader是加载属性A时设置的
// 则此时ResultLoader中的Executor在ResultLoader中被替换成了一个能运行的Executor，而不是ClosedExecutor
// 能运行的Executor的状态可能不是close，这将导致它被复用，从而引发多线程问题
// 是不是被两次执行的一个关键点就是有没有经过序列化，因为执行完后会被序列化并持久化
final ResultLoader old = this.resultLoader;
this.resultLoader = new ResultLoader(old.configuration, new ClosedExecutor(), old.mappedStatement,
old.parameterObject, old.targetType, old.cacheKey, old.boundSql);
}
this.metaResultObject.setValue(property, this.resultLoader.loadResult());
}
private Configuration getConfiguration() {
if (this.configurationFactory == null) {
throw new ExecutorException("Cannot get Configuration as configuration factory was not set.");
}
Object configurationObject;
try {
final Method factoryMethod = this.configurationFactory.getDeclaredMethod(FACTORY_METHOD);
if (!Modifier.isStatic(factoryMethod.getModifiers())) {
throw new ExecutorException("Cannot get Configuration as factory method ["
+ this.configurationFactory + "]#["
+ FACTORY_METHOD + "] is not static.");
}
if (!factoryMethod.isAccessible()) {
configurationObject = AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
try {
factoryMethod.setAccessible(true);
return factoryMethod.invoke(null);
} finally {
factoryMethod.setAccessible(false);
}
});
} else {
configurationObject = factoryMethod.invoke(null);
}
} catch (final ExecutorException ex) {
throw ex;
} catch (final NoSuchMethodException ex) {
throw new ExecutorException("Cannot get Configuration as factory class ["
+ this.configurationFactory + "] is missing factory method of name ["
+ FACTORY_METHOD + "].", ex);
} catch (final PrivilegedActionException ex) {
throw new ExecutorException("Cannot get Configuration as factory method ["
+ this.configurationFactory + "]#["
+ FACTORY_METHOD + "] threw an exception.", ex.getCause());
} catch (final Exception ex) {
throw new ExecutorException("Cannot get Configuration as factory method ["
+ this.configurationFactory + "]#["
+ FACTORY_METHOD + "] threw an exception.", ex);
}
if (!(configurationObject instanceof Configuration)) {
throw new ExecutorException("Cannot get Configuration as factory method ["
+ this.configurationFactory + "]#["
+ FACTORY_METHOD + "] didn't return [" + Configuration.class + "] but ["
+ (configurationObject == null ? "null" : configurationObject.getClass()) + "].");
}
return Configuration.class.cast(configurationObject);
}
private Log getLogger() {
if (this.log == null) {
this.log = LogFactory.getLog(this.getClass());
}
return this.log;
}
}
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