SpringSpring IOC原理及源码解析之scope=requestsession
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一、容器
1. 容器
抛出一个议点:BeanFactory是IOC容器,而ApplicationContex则是Spring容器。
什么是容器?Collection和Container这两个单词都有存放什么东西的意思,但是放在程序猿的世界,却注定是千差万别。Collection,集合,存放obj instanceof Class为true的一类对象,重点在于存放;Container,容器,可以存放各种各样的obj,但不仅仅是存放,他被称为容器,更重要的是他能管理存放对象的生命周期和依赖。
容器:用于存放对象,并能对存放对象进行生命周期管理和依赖管理。
2. Spring IOC容器是BeanFactory
Spring IOC容器是BeanFactory,也正是基于【容器】的论点。
在逻辑和源码分析之前,先做一些铺垫。对于使用Spring的程序猿来说,常用是ApplicationContext接口及其实现子类,ClasPathXmlApplicationContext、FilesystemXmlApplicationContext、XmlWebApplicationContext和AnnotationConfigWebApplicationContext,对于这四个类来说,他们都有一个共同的抽象父类AbstractRefreshableApplicationContext,而正是在该抽象父类中完成对BeanFactory的装饰。
public abstract class AbstractRefreshableApplicationContext extends AbstractApplicationContext { private Boolean allowBeanDefinitionOverriding; private Boolean allowCircularReferences; /** Bean factory for this context */ private DefaultListableBeanFactory beanFactory;
所有通过ApplicationContext接入使用Spring服务的,都是使用该bean工厂,而且最重要的是这个bean工厂实现了所有BeanFactory的接口、抽象类,拥有完整的Spring IOC逻辑。
二、Spring IOC逻辑
- BeanFactory在Spring容器初始化的时候创建,默认创建的是DefaultListableBeanFactory对象;
- Bean的配置信息在Spring容器初始化的时候被加载,并被解析成BeanDefinition存放在DefaultListableBeanFactory的ConcurrentHashMap中,此时无论是单例、非单例Bean都没有被创建;
- BeanFactory:直接通过BeanFactory来接入使用Spring,无论是单例、非单例的Bean都不会在Spring初始化的时候被创建,而是在第一次getBean的是时候才被创建,此时单例bean会被缓存,而非单例的bean不会被缓存;
- ApplicationContext:直接通过ApplicationContext来介入使用Spring,单例并且非lazy-init的Bean在Spring初始化的时候被创建并缓存,非单例、lazy-init的Bean在第一次getBean的时候被创建(Spring容器初始化的refresh方法中,finishBeanFactoryInitialization(beanFactory)方法完成);
- 所有Bean的依赖注入在getBean逻辑中完成,当然是在getBean实例化对象之后;
- 对于web环境下scope为request、session、globalsession的Bean来说,通过RequestContextListener侦听器侦听Request的建立和销毁,从而进行Bean生命周期的管理,具体是RequestContextHolder中通过ThreadLocal将ServletRequestAttributes与当前线程绑定,ServletRequestAttributes构造方法传入HttpServletRequest进行绑定,所有Bean第一次获取的时候会被缓存到ServletRequestAttributes中(因为传入了request,实际上最终存入了request的map容器中),之后直接从ServletRequestAttributes中获取不再进行创建;
三、源码分析
1. BeanFactory的创建
第一节已经说过ApplicationContext常用的的四个子类都有一个公共的抽象父类AbstractRefreshableApplicationContext,在该类中对BeanFactory进行装饰,一个更重要的点是AbstractRefreshableApplicationContext的父类是AbstractApplicationContext,其refresh方法定义了整个Spring容器启动的过程。
也就是说,无论你采用哪一种ApplicationContext接入Spring容器,最终都会进入AbstractApplicationContext的refresh方法,完成Spring的启动。
源码分析是基于Spring IOC中提出的五点逻辑,发现一篇写的很全面的文章,因此决定不再写了,贴出来共享。
《Spring:源码解读Spring IOC原理》
作为连接文章中未提及的web部分,本文予以补充,进行原理和源码的分析。
2. web Scope(request、session、globalsession)
如上文继承关系所述内容,无论是哪一种ApplicationContext,最终都是通过AbstractBeanFactory.getBean(String)来获取Bean,节选部分代码。
@Override public Object get(String name, ObjectFactory<?> objectFactory) { RequestAttributes attributes = RequestContextHolder.currentRequestAttributes(); Object scopedObject = attributes.getAttribute(name, getScope()); if (scopedObject == null) { scopedObject = objectFactory.getObject(); attributes.setAttribute(name, scopedObject, getScope()); } return scopedObject; }
// 从BeanDefinition中获取scope配置内容 String scopeName = mbd.getScope();
// this.scopes是一个Map<String, Scope>,用于存放Scope对象实例
// 这里如果是request则获取到RequestScope
// 如果是Session则获取到SessionScope final Scope scope = this.scopes.get(scopeName);
if (scope == null){throw new IllegalStateException("No Scope registered for scope ‘" + scopeName + "‘");}try {// 这里是重点// 通过Scope.get(String, ObjectFactory)接入到Spring IOC容器中 Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() { @Override public Object getObject() throws BeansException { beforePrototypeCreation(beanName); try { return createBean(beanName, mbd, args); } finally { afterPrototypeCreation(beanName); } } }); bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd); } catch (IllegalStateException ex) { throw new BeanCreationException(beanName, "Scope ‘" + scopeName + "‘ is not active for the current thread; " + "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", ex); }
关于Scope的类结构如下图所示。
AbstractRequestAttributeScope定义了get(beanName, ObjectFactory)方法,通过该方法接入Spring IOC容器,源码如下所示。
public Object get(String name, ObjectFactory<?> objectFactory) { // 这里很重要 // RequestContextHolder中通过ThreadLocal将RequestAttributes实例和当前线程绑定 // RequestAttributes在构造的时候需要传入HttpServletRequest,稍后会有源码分析和总结 RequestAttributes attributes = RequestContextHolder.currentRequestAttributes(); // 从当前线程绑定的RequestAttributes中获取对象(实际上是从HttpServletRequest的Map) // 如果已经实例化过了,则不再实例化 // 否则进入Spring IOC过程获取对象 Object scopedObject = attributes.getAttribute(name, getScope()); if (scopedObject == null) { scopedObject = objectFactory.getObject() attributes.setAttribute(name, scopedObject, getScope()); } return scopedObject; }
现在存在的疑问是RequestAttributes、RequestContextHolder是个什么鬼?从哪里来?
要想使用Spring web scope,在web.xml中要配置一个侦听器RequestContextListener,所有谜题的答案都在这里。
public class RequestContextListener implements ServletRequestListener { private static final String REQUEST_ATTRIBUTES_ATTRIBUTE = RequestContextListener.class.getName() + ".REQUEST_ATTRIBUTES"; @Override public void requestInitialized(ServletRequestEvent requestEvent) { if (!(requestEvent.getServletRequest() instanceof HttpServletRequest)) { throw new IllegalArgumentException( "Request is not an HttpServletRequest: " + requestEvent.getServletRequest()); } HttpServletRequest request = (HttpServletRequest) requestEvent.getServletRequest(); ServletRequestAttributes attributes = new ServletRequestAttributes(request); request.setAttribute(REQUEST_ATTRIBUTES_ATTRIBUTE, attributes); LocaleContextHolder.setLocale(request.getLocale()); RequestContextHolder.setRequestAttributes(attributes); } @Override public void requestDestroyed(ServletRequestEvent requestEvent) { ServletRequestAttributes attributes = null; Object reqAttr = requestEvent.getServletRequest().getAttribute(REQUEST_ATTRIBUTES_ATTRIBUTE); if (reqAttr instanceof ServletRequestAttributes) { attributes = (ServletRequestAttributes) reqAttr; } RequestAttributes threadAttributes = RequestContextHolder.getRequestAttributes(); if (threadAttributes != null) { // We‘re assumably within the original request thread... LocaleContextHolder.resetLocaleContext(); RequestContextHolder.resetRequestAttributes(); if (attributes == null && threadAttributes instanceof ServletRequestAttributes) { attributes = (ServletRequestAttributes) threadAttributes; } } if (attributes != null) { attributes.requestCompleted(); } } }
这句代码RequestContextHolder.setRequestAttributes(attributes)是将Spring web scope与Spring IOC结合的关键。
public abstract class RequestContextHolder {
// 将ServletRequestAttributes与当前线程绑定
private static final ThreadLocal<RequestAttributes> requestAttributesHolder = new NamedThreadLocal<RequestAttributes>("Request attributes");
private static final ThreadLocal<RequestAttributes> inheritableRequestAttributesHolder = new NamedInheritableThreadLocal<RequestAttributes>("Request context");
// 1 第一步 public static void setRequestAttributes(RequestAttributes attributes) { setRequestAttributes(attributes, false); }
// 2 第二步,inheritable=false public static void setRequestAttributes(RequestAttributes attributes, boolean inheritable)
{ if (attributes == null) { resetRequestAttributes(); }
else {
if (inheritable) { inheritableRequestAttributesHolder.set(attributes); requestAttributesHolder.remove(); }
else {
// 3 第三步,将ServletRequestAttributes与当前线程绑定 requestAttributesHolder.set(attributes); inheritableRequestAttributesHolder.remove(); } } } //其他源码,略 }
至此,整个过程结束。session的过程几乎和request一致,只是生命周期不一样,多了一把锁。总结一下上述源码分析的内容。
总结:Spring Bean所有scope定义为request、session、globalsession的Bean都不会主动初始化,当第一次通过Spring IOC来getBean的时候才会实例化并进行依赖注入,但是在实例化的时候需要借助于RequestContextHolder(ThreadLocal模式)来将Bean与当前线程中的HttpServletRequest来进行绑定,并在scope的生命周期中缓存在相应的域对象中(request或session)。
最后补充一点,ServletRequestAttributes的getAttribute和setAttribute。在getBean的时候,会先从ServletRequestAttributes.getAttribute中获取Bean,如果获取到则返回,否则进行IOC实例化,并调用ServletRequestAttributes.setArrtibute进行缓存,实际上在setAttribute方法中是调用request.setAttribute来完成。
public class ServletRequestAttributes extends AbstractRequestAttributes {
public static final String DESTRUCTION_CALLBACK_NAME_PREFIX = ServletRequestAttributes.class.getName() + ".DESTRUCTION_CALLBACK.";
private final HttpServletRequest request; private HttpServletResponse response;
private volatile HttpSession session;
private final Map<String, Object> sessionAttributesToupdate = new ConcurrentHashMap<String, Object>(1);
// 1 ServletRequestAttributes对象的创建,必须要一个HttpServletRequest实例
public ServletRequestAttributes(HttpServletRequest request) {
Assert.notNull(request, "Request must not be null"); this.request = request; }
public ServletRequestAttributes(HttpServletRequest request, HttpServletResponse response) { this(request); this.response = response; }
// 转调request.getAttribute或session.getAttribute
public Object getAttribute(String name, int scope) { if (scope == SCOPE_REQUEST) { if (!isRequestActive()) { throw new IllegalStateException( "Cannot ask for request attribute - request is not active anymore!"); } return this.request.getAttribute(name); } else { HttpSession session = getSession(false); if (session != null) { try { Object value =session.getAttribute(name); if (value != null) { this.sessionAttributesToUpdate.put(name, value); } return value; } catch (IllegalStateException ex) { // Session invalidated - shouldn‘t usually happen. } } return null; } }
// 转调reqeust.setAttribute或session。setAttribute public void setAttribute(String name, Object value, int scope) { if (scope == SCOPE_REQUEST) { if (!isRequestActive()) { throw new IllegalStateException( "Cannot set request attribute - request is not active anymore!"); } this.request.setAttribute(name, value); } else { HttpSession session = getSession(true); this.sessionAttributesToUpdate.remove(name); session.setAttribute(name, value); } }
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