Scope实现原理

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spring3.x

内置Scope分类
Singleton 每个IOC容器对一个bean定义创建唯一实例
Prototype 对一个bean定义，每次请求容器都会创建新的实例
Request 对一个bean定义，一次web请求会创建一个实例
Session 对一个bean定义，一次web会话创建一个实例
Global Session 对一个bean定义，一次porlet会话创建一个实例
后三种只在Web环境下使用，AbstractApplicationContext refresh入口

AbstractRefreshableWebApplicationContext会注册这三种BEAN

WebApplicationContextUtils具体代码

当使用AbstractRefreshableWebApplicationContext并不会注册这三种Bean.
这三种Scope父类方法调用RequestContextHolder

在RequestContextHolder实现中，RequestAttribute为空，则抛出错误

RequestAttribute的实现ServletRequestAttributes中，封装了HTTP对象和Scope的Bean获取，设置和销毁方法

所以在WEB环境下，如果使用SPRING MVC,则在 DispatcherServlet, or DispatcherPortlet已经初始化RequestAttribute对象，否则必须做相关配置以初始化。
使用servlet2.4+容器，web.xml配置如下

<web-app>
...
<listener>
  <listener-class>
      org.springframework.web.context.request.RequestContextListener
  </listener-class>
</listener>
...
</web-app>

servlet2.3,web配置如下

<web-app>
..
<filter>
  <filter-name>requestContextFilter</filter-name>
  <filter-class>org.springframework.web.filter.RequestContextFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>requestContextFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>
...
</web-app>

RequestContextFilter初始化RequestAtrributes

Scope只有在getBean中有效
Spring不仅负责Bean的实例化，而且还管理依赖关系，根据依赖仅仅会在第一次请求时创建和装配好bean。因此：如果在bean定义中只是指定了scope，则除了singleton，其他的scope定义的bean实例的含义是无效的，必须钩入向Spring容器请求，也就是调用getBean方法。换句话说，我们必须改变依赖关系的注入。可以想到使用代理作为被注入的对象，当调用代理方法时，会实时的getBean 请求容器。实现这种机制的是 <aop:scoped-proxy/>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:aop="http://www.springframework.org/schema/aop"
     xsi:schemaLocation="http://www.springframework.org/schema/beans
         http://www.springframework.org/schema/beans/spring-beans.xsd
         http://www.springframework.org/schema/aop
         http://www.springframework.org/schema/aop/spring-aop.xsd">

  <!-- an HTTP Session-scoped bean exposed as a proxy -->
  <bean id="userPreferences" class="com.foo.UserPreferences" scope="session">

        <!-- instructs the container to proxy the surrounding bean -->
        <aop:scoped-proxy/>
  </bean>

  <!-- a singleton-scoped bean injected with a proxy to the above bean -->
  <bean id="userService" class="com.foo.SimpleUserService">

      <!-- a reference to the proxied userPreferences bean -->
      <property name="userPreferences" ref="userPreferences"/>

  </bean>
</beans>

我们插入了<aop:scoped-proxy/>元素在被注入的userPreferences定义中，为什么scope等于request,session, global session,或自定义的scope bean需要这样？对比下面的定义

<bean id="userPreferences" class="com.foo.UserPreferences" scope="session"/>

<bean id="userManager" class="com.foo.UserManager">
  <property name="userPreferences" ref="userPreferences"/>
</bean>

上面的例子中userManager被注入了一个scope等于HTTP session的bean userPreferences.userManager是单例的，它只会在每个容器中初始化一次，他所依赖的Bean也只会初始化一次。就是说userManager只会在一个userPreferences上操作，就是在第一次初始化的userPreferences上。
把生命周期短的注入到生命周期长的bean，可能不是想要的结果，就比如把session scope的bean注入到一个单例Bean中。你需要单例Bean负责Http session bean的特定于Http Session生命周期。因此容器创建了userPreferences的代理对象，把它注入到userManager，但userManager并不知道userPreferences是个代理对象。当userManager调用userPreferences实例的方法时，其实调用的是代理对象的方法。代理对象会请求真正的Bean并调用之上的方法。
同时可以选择创建代理的方式 JDK接口或CGLIB类方式，MethodInjection之中有讨论。默认情况下会使用CGLIB方式，如果想使用JDK动态代理，则作如下配置。

<!-- DefaultUserPreferences implements the UserPreferences interface -->
<bean id="userPreferences" class="com.foo.DefaultUserPreferences" scope="session">
  <aop:scoped-proxy proxy-target-class="false"/>
</bean>

<bean id="userManager" class="com.foo.UserManager">
  <property name="userPreferences" ref="userPreferences"/>
</bean>

ScopedProxyFactoryBean实现<aop:scoped-proxy/>
spring-beans DTD 或者 XSD的解析者DefaultBeanDefinitionDocumentReader
解析根元素及代理BeanDefinitionParserDelegate解析其他的子元素
根元素有beans，alias，import

/**
	 * Parse the elements at the root level in the document:
	 * "import", "alias", "bean".
	 * @param root the DOM root element of the document
	 */
	protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		if (delegate.isDefaultNamespace(root)) {
			NodeList nl = root.getChildNodes();
			for (int i = 0; i < nl.getLength(); i++) {
				Node node = nl.item(i);
				if (node instanceof Element) {
					Element ele = (Element) node;
					if (delegate.isDefaultNamespace(ele)) {
						parseDefaultElement(ele, delegate);
					}
					else {
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}

	private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
		if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
			importBeanDefinitionResource(ele);
		}
		else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
			processAliasRegistration(ele);
		}
		else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
			processBeanDefinition(ele, delegate);
		}
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
	}

子元素的解析者BeanDefinitionParserDelegate，当一个bean定义解析好之后，要进一步进行可能的自定义属性或内置元素的解析，进入decorateIfRequired方法。

NamespaceHandler命名空间处理器，比如<aop:.../>将使用AOPNamespaceHandler.
DefaultNamespaceHandlerResolver将会在所有的JAR包中查找META-INF/spring.handlers并读入，在JAR spring-aop下有META-INF/spring.handlers
内容为
http\://www.springframework.org/schema/aop=org.springframework.aop.config.AopNamespaceHandler
在JAR spring-bean下有META-INF/spring.handlers，内容为
http\://www.springframework.org/schema/c=org.springframework.beans.factory.xml.SimpleConstructorNamespaceHandler
http\://www.springframework.org/schema/p=org.springframework.beans.factory.xml.SimplePropertyNamespaceHandler
http\://www.springframework.org/schema/util=org.springframework.beans.factory.xml.UtilNamespaceHandler
载入资源代码

AopNamespaceHandler实现中可以看到config用于事务处理的；aspectj-autoproxy用于aspectj自动代理的；scoped-proxy用于Scope bean处理的；所以<aop:scoped-proxy/>将由ScopedProxyBeanDefinitionDecorator处理

ScopedProxyBeanDefinitionDecorator最终代理ScopedProxyUtils.createScopedProxy
1.创建一个ScopedProxyFactoryBean对应的代理RootBeanDefinition
2.占有了Scope bean的标识符，可能的候选者（当以类型装配查找时）
3.Scope bean的名字为标识符变成 "scopedTarget." + ID ,同时丧失候选资格

String originalBeanName = definition.getBeanName();
		BeanDefinition targetDefinition = definition.getBeanDefinition();

		// Create a scoped proxy definition for the original bean name,
		// "hiding" the target bean in an internal target definition.
		RootBeanDefinition proxyDefinition = new RootBeanDefinition(ScopedProxyFactoryBean.class);
		proxyDefinition.setOriginatingBeanDefinition(definition.getBeanDefinition());
		proxyDefinition.setSource(definition.getSource());
		proxyDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);

		String targetBeanName = getTargetBeanName(originalBeanName);
		proxyDefinition.getPropertyValues().add("targetBeanName", targetBeanName);

		if (proxyTargetClass) {
			targetDefinition.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
			// ScopedFactoryBean's "proxyTargetClass" default is TRUE, so we don't need to set it explicitly here.
		}
		else {
			proxyDefinition.getPropertyValues().add("proxyTargetClass", Boolean.FALSE);
		}

		// Copy autowire settings from original bean definition.
		proxyDefinition.setAutowireCandidate(targetDefinition.isAutowireCandidate());
		proxyDefinition.setPrimary(targetDefinition.isPrimary());
		if (targetDefinition instanceof AbstractBeanDefinition) {
			proxyDefinition.copyQualifiersFrom((AbstractBeanDefinition) targetDefinition);
		}

		// The target bean should be ignored in favor of the scoped proxy.
		targetDefinition.setAutowireCandidate(false);
		targetDefinition.setPrimary(false);

		// Register the target bean as separate bean in the factory.
		registry.registerBeanDefinition(targetBeanName, targetDefinition);

		// Return the scoped proxy definition as primary bean definition
		// (potentially an inner bean).
		return new BeanDefinitionHolder(proxyDefinition, originalBeanName, definition.getAliases());

ScopedProxyFactoryBean实现
1.setProxyTargetClass设置代理方式,true为CGliB代理，false为JDK代理
2.scopedTargetSource = new SimpleBeanTargetSource()代理方法每调用一次，就会向Spring容器发送getBean请求
3.添加AopInfrastructureBean接口，生成代理对象；说明代理对象类型并不适合自动代理机制
4.添加DelegatingIntroductionInterceptor introduction借口，并暴露DefaultScopedObject对象，生成代理；所以可以编程式把代理对象转化ScopedObject对象而从scope中进行获取和移除bean

/*
 * Copyright 2002-2009 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.springframework.aop.scope;

import java.lang.reflect.Modifier;

import org.springframework.aop.framework.AopInfrastructureBean;
import org.springframework.aop.framework.ProxyConfig;
import org.springframework.aop.framework.ProxyFactory;
import org.springframework.aop.support.DelegatingIntroductionInterceptor;
import org.springframework.aop.target.SimpleBeanTargetSource;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.FactoryBeanNotInitializedException;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.util.ClassUtils;

/**
 * Convenient proxy factory bean for scoped objects.
 * 
 * <p>Proxies created using this factory bean are thread-safe singletons
 * and may be injected into shared objects, with transparent scoping behavior.
 *
 * <p>Proxies returned by this class implement the {@link ScopedObject} interface.
 * This presently allows for removing the corresponding object from the scope,
 * seamlessly creating a new instance in the scope on next access.
 * 
 * <p>Please note that the proxies created by this factory are
 * <i>class-based</i> proxies by default. This can be customized
 * through switching the "proxyTargetClass" property to "false".
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 2.0
 * @see #setProxyTargetClass
 */
public class ScopedProxyFactoryBean extends ProxyConfig implements FactoryBean<Object>, BeanFactoryAware {

	/** The TargetSource that manages scoping */
	private final SimpleBeanTargetSource scopedTargetSource = new SimpleBeanTargetSource();

	/** The name of the target bean */
	private String targetBeanName;

	/** The cached singleton proxy */
	private Object proxy;


	/**
	 * Create a new ScopedProxyFactoryBean instance.
	 */
	public ScopedProxyFactoryBean() {
		setProxyTargetClass(true);
	}


	/**
	 * Set the name of the bean that is to be scoped.
	 */
	public void setTargetBeanName(String targetBeanName) {
		this.targetBeanName = targetBeanName;
		this.scopedTargetSource.setTargetBeanName(targetBeanName);
	}

	public void setBeanFactory(BeanFactory beanFactory) {
		if (!(beanFactory instanceof ConfigurableBeanFactory)) {
			throw new IllegalStateException("Not running in a ConfigurableBeanFactory: " + beanFactory);
		}
		ConfigurableBeanFactory cbf = (ConfigurableBeanFactory) beanFactory;

		this.scopedTargetSource.setBeanFactory(beanFactory);

		ProxyFactory pf = new ProxyFactory();
		pf.copyFrom(this);
		pf.setTargetSource(this.scopedTargetSource);

		Class beanType = beanFactory.getType(this.targetBeanName);
		if (beanType == null) {
			throw new IllegalStateException("Cannot create scoped proxy for bean '" + this.targetBeanName +
					"': Target type could not be determined at the time of proxy creation.");
		}
		if (!isProxyTargetClass() || beanType.isInterface() || Modifier.isPrivate(beanType.getModifiers())) {
			pf.setInterfaces(ClassUtils.getAllInterfacesForClass(beanType, cbf.getBeanClassLoader()));
		}

		// Add an introduction that implements only the methods on ScopedObject.
		ScopedObject scopedObject = new DefaultScopedObject(cbf, this.scopedTargetSource.getTargetBeanName());
		pf.addAdvice(new DelegatingIntroductionInterceptor(scopedObject));

		// Add the AopInfrastructureBean marker to indicate that the scoped proxy
		// itself is not subject to auto-proxying! Only its target bean is.
		pf.addInterface(AopInfrastructureBean.class);

		this.proxy = pf.getProxy(cbf.getBeanClassLoader());
	}


	public Object getObject() {
		if (this.proxy == null) {
			throw new FactoryBeanNotInitializedException();
		}
		return this.proxy;
	}

	public Class<?> getObjectType() {
		if (this.proxy != null) {
			return this.proxy.getClass();
		}
		if (this.scopedTargetSource != null) {
			return this.scopedTargetSource.getTargetClass();
		}
		return null;
	}

	public boolean isSingleton() {
		return true;
	}

}

自定义scope
编写了Scope实现之后，要将他注册到Spring容器中，下面是核心注册方法
void registerScope(String scopeName, Scope scope);
这个方法在ConfigurableBeanFactory中声明，大多数ApplicationContext都实现了它。
方法中的第一个参数是scope的名字，用于配置bean指定scope时使用，第二个参数是具体实现。
编程式的注册

Scope threadScope = new SimpleThreadScope();
beanFactory.registerScope("thread", threadScope);

xml配置

<bean id="..." class="..." scope="thread">

声明式注册
xml配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:aop="http://www.springframework.org/schema/aop"
     xsi:schemaLocation="http://www.springframework.org/schema/beans
         http://www.springframework.org/schema/beans/spring-beans.xsd
         http://www.springframework.org/schema/aop
         http://www.springframework.org/schema/aop/spring-aop.xsd">

  <bean class="org.springframework.beans.factory.config.CustomScopeConfigurer">
      <property name="scopes">
          <map>
              <entry key="thread">
                  <bean class="org.springframework.context.support.SimpleThreadScope"/>
              </entry>
          </map>
      </property>
  </bean>

  <bean id="bar" class="x.y.Bar" scope="thread">
      <property name="name" value="Rick"/>
      <aop:scoped-proxy/>
  </bean>

  <bean id="foo" class="x.y.Foo">
      <property name="bar" ref="bar"/>
  </bean>

</beans>

实现
AbstractApplicationContext入口 refresh

显然所有的BeanFactoryPostProcessor会在此处被调用，包括注册Scope的CustomScopeConfigurer，因为它是一个BeanFactoryPostProcessor实例。

	@SuppressWarnings("unchecked")
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		if (this.scopes != null) {
			for (Map.Entry<String, Object> entry : this.scopes.entrySet()) {
				String scopeKey = entry.getKey();
				Object value = entry.getValue();
				if (value instanceof Scope) {
					beanFactory.registerScope(scopeKey, (Scope) value);
				}
				else if (value instanceof Class) {
					Class scopeClass = (Class) value;
					Assert.isAssignable(Scope.class, scopeClass);
					beanFactory.registerScope(scopeKey, (Scope) BeanUtils.instantiateClass(scopeClass));
				}
				else if (value instanceof String) {
					Class scopeClass = ClassUtils.resolveClassName((String) value, this.beanClassLoader);
					Assert.isAssignable(Scope.class, scopeClass);
					beanFactory.registerScope(scopeKey, (Scope) BeanUtils.instantiateClass(scopeClass));
				}
				else {
					throw new IllegalArgumentException("Mapped value [" + value + "] for scope key [" +
							scopeKey + "] is not an instance of required type [" + Scope.class.getName() +
							"] or a corresponding Class or String value indicating a Scope implementation");
				}
			}
		}
	}

那不得不提的是BeanFactoryPostProcessor的调用情况
1.可以编程式的添加BeanFactoryPostProcessor和对于BeanFactory是BeanDefinitionRegistry类型的可以声明式的注册BeanFactoryPostProcessor实例
2.BeanFactoryPostProcessor的子类BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法被调用
3.调用顺序为:
     编程式添加的BeanFactoryPostProcessor子类实例的postProcessBeanDefinitionRegistry方法
      声明式注册的BeanFactoryPostProcessor子类实例的postProcessBeanDefinitionRegistry方法
      编程式添加的BeanFactoryPostProcessor子类实例的postProcessBeanFactory方法
      声明式注册的BeanFactoryPostProcessor子类实例的postProcessBeanFactory方法
      编程式添加的BeanFactoryPostProcessor实例的postProcessBeanFactory方法
      声明式注册的BeanFactoryPostProcessor实现PriorityOrdered接口实例的postProcessBeanFactory方法
      声明式注册的BeanFactoryPostProcessor实现Ordered接口实例的postProcessBeanFactory方法
      声明式注册的BeanFactoryPostProcessor没有实现PriorityOrdered或Ordered接口实例的postProcessBeanFactory方法

/**
	 * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
	 * respecting explicit order if given.
	 * <p>Must be called before singleton instantiation.
	 */
	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		// Invoke BeanDefinitionRegistryPostProcessors first, if any.
		Set<String> processedBeans = new HashSet<String>();
		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
			List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
					new LinkedList<BeanDefinitionRegistryPostProcessor>();
			for (BeanFactoryPostProcessor postProcessor : getBeanFactoryPostProcessors()) {
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
					BeanDefinitionRegistryPostProcessor registryPostProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
					registryPostProcessors.add(registryPostProcessor);
				}
				else {
					regularPostProcessors.add(postProcessor);
				}
			}
			Map<String, BeanDefinitionRegistryPostProcessor> beanMap =
					beanFactory.getBeansOfType(BeanDefinitionRegistryPostProcessor.class, true, false);
			List<BeanDefinitionRegistryPostProcessor> registryPostProcessorBeans =
					new ArrayList<BeanDefinitionRegistryPostProcessor>(beanMap.values());
			OrderComparator.sort(registryPostProcessorBeans);
			for (BeanDefinitionRegistryPostProcessor postProcessor : registryPostProcessorBeans) {
				postProcessor.postProcessBeanDefinitionRegistry(registry);
			}
			invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(registryPostProcessorBeans, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
			processedBeans.addAll(beanMap.keySet());
		}
		else {
			// Invoke factory processors registered with the context instance.
			invokeBeanFactoryPostProcessors(getBeanFactoryPostProcessors(), beanFactory);
		}

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let the bean factory post-processors apply to them!
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

		// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
		List<String> orderedPostProcessorNames = new ArrayList<String>();
		List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
		for (String ppName : postProcessorNames) {
			if (processedBeans.contains(ppName)) {
				// skip - already processed in first phase above
			}
			else if (isTypeMatch(ppName, PriorityOrdered.class)) {
				priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
			}
			else if (isTypeMatch(ppName, Ordered.class)) {
				orderedPostProcessorNames.add(ppName);
			}
			else {
				nonOrderedPostProcessorNames.add(ppName);
			}
		}

		// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
		OrderComparator.sort(priorityOrderedPostProcessors);
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

		// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
		List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
		for (String postProcessorName : orderedPostProcessorNames) {
			orderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		OrderComparator.sort(orderedPostProcessors);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

		// Finally, invoke all other BeanFactoryPostProcessors.
		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
		for (String postProcessorName : nonOrderedPostProcessorNames) {
			nonOrderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
	}