标签:tle ceo tomcat源码 closed character 配置信息 event init 设计模式
首先回归一下web.xml的常用配置,看一个示例:
<context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath*:spring/applicationcontext-*.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <filter> <filter-name>encodingFilter</filter-name> <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class> <init-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value> </init-param> <init-param> <param-name>forceEncoding</param-name> <param-value>true</param-value> </init-param> </filter> <filter-mapping> <filter-name>encodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <servlet> <servlet-name>springmvc</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath*:spring/springmvc-context.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>springmvc</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping>
了解web.xml的作用之前必须要了解web容器(也称为是servlet容器)这个概念,常用的web容器有Tomcat、Jetty、JBoss等。
使用web容器,就不得不清楚什么是ServletContext。ServletContext中的信息都是由容器提供的,在web容器启动时,它作为为公共环境容器存放公共信息,为各个Servlet提供信息,也可以作为各个Servlet之间通信的桥梁。
将应用部署到web容器中,启动web容器后,web容器会读取web.xml中的配置信息,对ServletContext进行信息补充。
好了,回到本文主题。
web.xml中的配置文件中ContextLoaderListener作为监听器,会监听web容器相关事件,在web容器启动或者关闭时触发执行响应程序。具体地,ContextLoaderListener继承ContextLoader类并实现了ServletContextListener接口。
public class ContextLoaderListener extends ContextLoader implements ServletContextListener { public ContextLoaderListener() { } public ContextLoaderListener(WebApplicationContext context) { super(context); } public void contextInitialized(ServletContextEvent event) { this.initWebApplicationContext(event.getServletContext()); } public void contextDestroyed(ServletContextEvent event) { this.closeWebApplicationContext(event.getServletContext()); ContextCleanupListener.cleanupAttributes(event.getServletContext()); } }
ServletContextListener接口中只有初始化和销毁的两个方法::
public interface ServletContextListener extends EventListener { /** ** Notification that the web application initialization ** process is starting. ** All ServletContextListeners are notified of context ** initialization before any filter or servlet in the web ** application is initialized. */ public void contextInitialized ( ServletContextEvent sce ); /** ** Notification that the servlet context is about to be shut down. ** All servlets and filters have been destroy()ed before any ** ServletContextListeners are notified of context ** destruction. */ public void contextDestroyed ( ServletContextEvent sce ); }
也就是监听ServletContext的状态,ServletContext属于容器对象,在用于在容器开启或关闭时触发事件,执行contextInitialized/contextDestroyed 。如果想了解程序执行原由可以先了解事件监听设计模式。查阅Tomcat源码,tomcat触发ServletContext初始化监听事件的源码如下:
...(部分略) Object instances[] = getApplicationLifecycleListeners(); for (int i = 0; i < instances.length; i++) { if (!(instances[i] instanceof ServletContextListener)) continue; ServletContextListener listener = (ServletContextListener) instances[i]; try { if (noPluggabilityListeners.contains(listener)) { listener.contextInitialized(tldEvent); } else { listener.contextInitialized(event); } } catch (Throwable t) { } } ...(部分略)
也就是,遍历所有ServletContextListener,调用监听方法。
关于功能主要看initWebApplicationContext()方法,ContextLoaderListener继承ContextLoader,ContextLoader中的initWebApplicationContext()方法中会创建WebApplicationContext上下文对象,并将这个对象设置到servletContext中:
ContextLoaderListener加载过程:
initWebApplicationContext调用createWebApplicationContext方法;
-->createWebApplicationContext 调用determineContextClass方法
--> defaultStrategies中加载配置文件:
defaultStrategies.getProperty(WebApplicationContext.class.getName())
ContextLoader 类中有段静态代码:
static { try { ClassPathResource resource = new ClassPathResource( "ContextLoader.properties", ContextLoader.class); defaultStrategies = PropertiesLoaderUtils.loadProperties(resource); } catch (IOException ex) { throw new IllegalStateException( "Could not load ‘ContextLoader.properties‘: " + ex.getMessage()); } currentContextPerThread = new ConcurrentHashMap(1); }
ContextLoader.properties 文件内容如下:
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext
可知,默认加载的WebApplicationContext是XmlWebApplicationContext
题外话,如果你不想使用默认的,在web.xml中配置contextClass即可
protected Class<?> determineContextClass(ServletContext servletContext) { String contextClassName = servletContext.getInitParameter("contextClass"); if(contextClassName != null) { try { return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader()); ...(略)
也就是这种形式:
<context-param>
<param-name>contextClass</param-name>
<param-value>webApplicationContext类全路径名称</param-value>
<context-param>
到org.springframework.web.context.support
包下查询webApplicationContext。
这一步主要是调用configureAndRefreshWebApplicationContext,可知在上一步中创建了WebApplicationContext对象(ConfigurableApplicationContext类型),也就是创建了IOC容器对象,接着就要给这个对象进行配置参数的设置了。
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) { String configLocationParam; if(ObjectUtils.identityToString(wac).equals(wac.getId())) { configLocationParam = sc.getInitParameter("contextId"); if(configLocationParam != null) { wac.setId(configLocationParam); } else { wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath())); } } wac.setServletContext(sc); configLocationParam = sc.getInitParameter("contextConfigLocation"); if(configLocationParam != null) { wac.setConfigLocation(configLocationParam); } ConfigurableEnvironment env = wac.getEnvironment(); if(env instanceof ConfigurableWebEnvironment) { ((ConfigurableWebEnvironment)env).initPropertySources(sc, (ServletConfig)null); } this.customizeContext(sc, wac); wac.refresh(); }
可知,首先会给WebApplicationContext对象设置ServletContext全局信息,然后读取><param-name>contextConfigLocation</param-name>对应的.xml中的配置信息,例如:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath*:spring/applicationcontext-*.xml</param-value>
</context-param>
这些applicationcontext-*.xml配置文件中的信息之后再执行ConfigurableApplicationContext.refresh()方法就会被加载到IOC容器中。
IOC容器的初始化过程,参考下一篇文章。
springmvc web.xml配置之ContextLoaderListener
标签:tle ceo tomcat源码 closed character 配置信息 event init 设计模式
原文地址:https://www.cnblogs.com/chenjunjie12321/p/9357534.html