Spring的refresh()方法相关异常解析
spring是一个开放源代码的设计层面框架,他解决的是业务逻辑层和其他各层的松耦合问题,因此它将面向接口的编程思想贯穿整个系统应用。spring是于2003 年兴起的一个轻量级的java 开发框架,由rod johnson创建。简单来说,spring是一个分层的javase/eefull-stack(一站式) 轻量级开源框架。
如果是经常使用spring,特别有自己新建applicationcontext对象的经历的人,肯定见过这么几条异常消息:
1.lifecycleprocessornotinitialized-call'refresh'beforeinvokinglifecyclemethodsviathecontext:......
2.beanfactorynotinitializedoralreadyclosed-call'refresh'beforeaccessingbeansviatheapplicationcontext
3.applicationeventmulticasternotinitialized-call'refresh'beforemulticastingeventsviathecontext:......
第一条消息是说lifecycleprocessor对象没有初始化,在调用context的生命周期方法之前必须调用'refresh'方法
第二条消息是说beanfactory对象没有初始化或已经关闭了,使用applicationcontext获取bean之前必须调用'refresh'方法
第三条消息是说applicationeventmulticaster对象没有初始化,在context广播事件之前必须调用'refresh'方法
这几条异常消息都与refresh方法有关,那抛出这些异常的原因到底是什么,为什么在这么多情况下一定要先调用refresh方法(定义在abstractapplicationcontext类中),在此这前我们先看看refresh方法中又干了些什么?
public void refresh() throws beansexception, illegalstateexception { synchronized (this.startupshutdownmonitor) { //刷新之前的准备工作,包括设置启动时间,是否激活标识位,初始化属性源(property source)配置 preparerefresh(); //由子类去刷新beanfactory(如果还没创建则创建),并将beanfactory返回 configurablelistablebeanfactory beanfactory = obtainfreshbeanfactory(); //准备beanfactory以供applicationcontext使用 preparebeanfactory(beanfactory); try { //子类可通过格式此方法来对beanfactory进行修改 postprocessbeanfactory(beanfactory); //实例化并调用所有注册的beanfactorypostprocessor对象 invokebeanfactorypostprocessors(beanfactory); //实例化并调用所有注册的beanpostprocessor对象 registerbeanpostprocessors(beanfactory); //初始化messagesource initmessagesource(); //初始化事件广播器 initapplicationeventmulticaster(); //子类覆盖此方法在刷新过程做额外工作 onrefresh(); //注册应用监听器applicationlistener registerlisteners(); //实例化所有non-lazy-init bean finishbeanfactoryinitialization(beanfactory); //刷新完成工作,包括初始化lifecycleprocessor,发布刷新完成事件等 finishrefresh(); } catch (beansexception ex) { // destroy already created singletons to avoid dangling resources. destroybeans(); // reset 'active' flag. cancelrefresh(ex); // propagate exception to caller. throw ex; } } }
与此三条异常消息相关的方法分别为:
finishrefresh();obtainfreshbeanfactory();initapplicationeventmulticaster();
protected void finishrefresh() { // //初始化lifecycleprocessor initlifecycleprocessor(); // propagate refresh to lifecycle processor first. getlifecycleprocessor().onrefresh(); // publish the final event. publishevent(new contextrefreshedevent(this)); // participate in livebeansview mbean, if active. livebeansview.registerapplicationcontext(this); }
如果没有调用finishrefresh方法,则lifecycleprocessor成员为null。
protected configurablelistablebeanfactory obtainfreshbeanfactory() { refreshbeanfactory();//刷新beanfactory,如果beanfactory为null,则创建 configurablelistablebeanfactory beanfactory = getbeanfactory(); if (logger.isdebugenabled()) { logger.debug("bean factory for " + getdisplayname() + ": " + beanfactory); } return beanfactory; }
refreshbeanfactory()为一抽象方法,真正实现在abstractrefreshableapplicationcontext类中:
@override protected final void refreshbeanfactory() throws beansexception { if (hasbeanfactory()) {//如果beanfactory已经不为null,则销毁beanfactory中的bean后自行关闭 destroybeans(); closebeanfactory(); } try { defaultlistablebeanfactory beanfactory = createbeanfactory();//创建beanfactory beanfactory.setserializationid(getid()); customizebeanfactory(beanfactory); loadbeandefinitions(beanfactory); synchronized (this.beanfactorymonitor) { this.beanfactory = beanfactory;//对beanfactory成员进行赋值 } } catch (ioexception ex) { throw new applicationcontextexception("i/o error parsing bean definition source for " + getdisplayname(), ex); } }
如果没有调用obtainfreshbeanfactory()方法则beanfactory成员为null。
protected void initapplicationeventmulticaster() { configurablelistablebeanfactory beanfactory = getbeanfactory(); if (beanfactory.containslocalbean(application_event_multicaster_bean_name)) { this.applicationeventmulticaster = beanfactory.getbean(application_event_multicaster_bean_name, applicationeventmulticaster.class); if (logger.isdebugenabled()) { logger.debug("using applicationeventmulticaster [" + this.applicationeventmulticaster + "]"); } } else { this.applicationeventmulticaster = new simpleapplicationeventmulticaster(beanfactory); beanfactory.registersingleton(application_event_multicaster_bean_name, this.applicationeventmulticaster); if (logger.isdebugenabled()) { logger.debug("unable to locate applicationeventmulticaster with name '" + application_event_multicaster_bean_name + "': using default [" + this.applicationeventmulticaster + "]"); } } }
而这三个方法调用都在refresh()方法中,由上面的分析可知,如果没有调用refresh方法,则上下文中的lifecycleprocessor,beanfactory,applicationeventmulticaster成员都会为null。至此可以来详细分析这三条异常消息的缘由了。
下面是针对上面三条异常消息的三段测试代码,顺序相对应:
1. public static void main(string[] args) { classpathxmlapplicationcontext applicationcontext = new classpathxmlapplicationcontext(); applicationcontext.setconfiglocation("application-context.xml"); applicationcontext.start(); applicationcontext.close(); } 2. public static void main(string[] args) { classpathxmlapplicationcontext applicationcontext = new classpathxmlapplicationcontext(); applicationcontext.setconfiglocation("application-context.xml"); applicationcontext.getbean("xtayfjpk"); applicationcontext.close(); } 3. public static void main(string[] args) { genericapplicationcontext parent = new genericapplicationcontext(); annotationconfigwebapplicationcontext context = new annotationconfigwebapplicationcontext(); context.setparent(parent); context.refresh(); context.start(); context.close(); }
对于第一条异常消息,异常堆栈出错在applicationcontext.start();下面是start()方法源码:
public void start() { getlifecycleprocessor().start(); publishevent(new contextstartedevent(this)); }
可以看到start()方法中要先获取lifecycleprocessor对象,而默认构造方法中并没用调用refresh方法,所以lifecycleprocessor为null,故而在getlifecycleprocessor()方法中抛出了此异常消息。这其中提到了生命周期方法,其实就是定义在org.springframework.context.lifecycle接口中的start(),stop(),isrunning()三个方法,如果是刚开始学习spring的话,创建classpathxmlapplicationcontext对象时应该是这样的:classpathxmlapplicationcontextapplicationcontext=newclasspathxmlapplicationcontext("application-context.xml");这样直接调用start()方法却又不会出现异常,这是为什么呢?这是因为classpathxmlapplicationcontext(stringconfiglocation)这个构造方法最终调用的是:
public classpathxmlapplicationcontext(string[] configlocations, boolean refresh, applicationcontext parent) throws beansexception { super(parent); setconfiglocations(configlocations); if (refresh) {//refresh传递值为true,这样就自动调用了refresh方法进行了刷新 refresh(); } }
第二条异常消息,异常堆栈出错在applicationcontext.getbean("xtayfjpk"),applicationcontext.getbean()方法调用的是上下文中beanfactory的getbean()方法实现的,获取beanfactory对象的代码在其基类configurablelistablebeanfactory中的getbeanfactory()方法中:
@override public final configurablelistablebeanfactory getbeanfactory() { synchronized (this.beanfactorymonitor) { if (this.beanfactory == null) { throw new illegalstateexception("beanfactory not initialized or already closed - " + "call 'refresh' before accessing beans via the applicationcontext"); } return this.beanfactory; } }
由于classpathxmlapplicationcontext的默认构造方法没有调用refresh()方法,所以beanfactory为null,因此抛出异常。
第三条异常消息,异常堆栈出错在context.refresh(),但是如果没有设置父上下文的话context.setparent(parent),例子代码是不会出现异常的。这是因为在refresh方法中的finishrefresh()方法调用了publishevent方法:
public void publishevent(applicationevent event) { assert.notnull(event, "event must not be null"); if (logger.istraceenabled()) { logger.trace("publishing event in " + getdisplayname() + ": " + event); } getapplicationeventmulticaster().multicastevent(event); if (this.parent != null) { this.parent.publishevent(event); } }
从上面可以看到:如果父上下文不为null,则还需要调用父容器的pushlishevent方法,而且在该方法中调用了getapplicationeventmulticaster()方法以获取一个事件广播器,问题就出现在这里:
private applicationeventmulticaster getapplicationeventmulticaster() throws illegalstateexception { if (this.applicationeventmulticaster == null) {//如果为null则抛异常 throw new illegalstateexception("applicationeventmulticaster not initialized - " + "call 'refresh' before multicasting events via the context: " + this); } return this.applicationeventmulticaster; }
而applicationeventmulticaster就是在refresh方法中的initapplicationeventmulticaster方法在实例化的,则于父上下文没有调用过refresh方法所以父上下文的applicationeventmulticaster成员为null,因此抛出异常。
综上所述,其实这三条异常消息的根本原因只有一个,就是当一个上下文对象创建后没有调用refresh()方法。在spring中applicationcontext实现类有很多,有些实现类在创建的过程中自动调用了refresh()方法,而有些又没有,如果没有则需要自己手动调用refresh()方法。一般说来实现webapplicationcontext接口的实现类以及使用默认构造方法创建上下文对象时不会自动refresh()方法,其它情况则会自动调用。
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