spring web项目启动入口
1、首先看一下传统Java Web的配置文件web.xml，网上找的一个，参考地址：https://blog.csdn.net/github_36301064/article/details/53290900
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1"> <servlet> <servlet-name>default</servlet-name> <servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class> <init-param> <param-name>debug</param-name> <param-value>0</param-value> </init-param> <init-param> <param-name>listings</param-name> <param-value>false</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet> <servlet-name>jsp</servlet-name> <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class> <init-param> <param-name>fork</param-name> <param-value>false</param-value> </init-param> <init-param> <param-name>xpoweredBy</param-name> <param-value>false</param-value> </init-param> <load-on-startup>3</load-on-startup> </servlet> <servlet-mapping> <servlet-name>default</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>jsp</servlet-name> <url-pattern>*.jsp</url-pattern> <url-pattern>*.jspx</url-pattern> </servlet-mapping> <session-config> <session-timeout>30</session-timeout> </session-config> <!-- 这里省略了大概4000多行的MIME类型的定义,这里只给出两种MIME类型的定义 --> <mime-mapping> <extension>bmp</extension> <mime-type>image/bmp</mime-type> </mime-mapping> <mime-mapping> <extension>htm</extension> <mime-type>text/html</mime-type> </mime-mapping> <welcome-file-list> <welcome-file>index.html</welcome-file> <welcome-file>index.htm</welcome-file> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app>
2、看一下spring web项目中的web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1"> <context-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/applicationContext.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <servlet> <servlet-name>dispatcher</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/dispatcher-servlet2.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>dispatcher</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <filter> <filter-name>CharacterEncodingFilter</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> </filter> <filter-mapping> <filter-name>CharacterEncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> </web-app>
dispatcher对应的servlet下的init-param可以不设置，默认使用/WEB-INF/dispatcher-servlet.xml
3、Tomcat等web容器启动干了什么，参考：https://blog.csdn.net/lieyanhaipo/article/details/58605545
容器启动的时候会调用 listen-class 的初始化事件，即 org.springframework.web.context.ContextLoaderListener 的初始化方法会被调用，同时 org.springframework.web.context.ContextLoaderListener 必须实现javax.servlet.ServletContextListener（Servlet）接口，
public void contextInitialized(ServletContextEvent sce); 接口中的初始化方法会被调用
public class ContextLoaderListener extends ContextLoader implements ServletContextListener { public ContextLoaderListener() { } public ContextLoaderListener(WebApplicationContext context) { super(context); } @Override public void contextInitialized(ServletContextEvent event) { initWebApplicationContext(event.getServletContext()); } @Override public void contextDestroyed(ServletContextEvent event) { closeWebApplicationContext(event.getServletContext()); ContextCleanupListener.cleanupAttributes(event.getServletContext()); } }
具体的实现在父类ContextLoader中
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) { throw new IllegalStateException( "Cannot initialize context because there is already a root application context present - " + "check whether you have multiple ContextLoader* definitions in your web.xml!"); } Log logger = LogFactory.getLog(ContextLoader.class); servletContext.log("Initializing Spring root WebApplicationContext"); if (logger.isInfoEnabled()) { logger.info("Root WebApplicationContext: initialization started");// spring web启动日志 } long startTime = System.currentTimeMillis(); try { // Store context in local instance variable, to guarantee that // it is available on ServletContext shutdown. if (this.context == null) { this.context = createWebApplicationContext(servletContext);// 创建WebApplicationContext，默认WebApplicationContext为XmlWebApplicationContext } if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; if (!cwac.isActive()) { // The context has not yet been refreshed -> provide services such as // setting the parent context, setting the application context id, etc if (cwac.getParent() == null) { // The context instance was injected without an explicit parent -> // determine parent for root web application context, if any. ApplicationContext parent = loadParentContext(servletContext); cwac.setParent(parent); } configureAndRefreshWebApplicationContext(cwac, servletContext); } } servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context); ClassLoader ccl = Thread.currentThread().getContextClassLoader(); if (ccl == ContextLoader.class.getClassLoader()) { currentContext = this.context; } else if (ccl != null) { currentContextPerThread.put(ccl, this.context); } if (logger.isDebugEnabled()) { logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]"); } if (logger.isInfoEnabled()) { long elapsedTime = System.currentTimeMillis() - startTime; logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");// spring web启动日志 } return this.context; } catch (RuntimeException ex) { logger.error("Context initialization failed", ex); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex); throw ex; } catch (Error err) { logger.error("Context initialization failed", err); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err); throw err; } }
创建上下文代码
protected WebApplicationContext createWebApplicationContext(ServletContext sc) { Class<?> contextClass = determineContextClass(sc); if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { throw new ApplicationContextException("Custom context class [" + contextClass.getName() + "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]"); } return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass); } /** * Return the WebApplicationContext implementation class to use, either the * default XmlWebApplicationContext or a custom context class if specified. * @param servletContext current servlet context * @return the WebApplicationContext implementation class to use * @see #CONTEXT_CLASS_PARAM * @see org.springframework.web.context.support.XmlWebApplicationContext */ protected Class<?> determineContextClass(ServletContext servletContext) { String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);// null if (contextClassName != null) { try { return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader()); } catch (ClassNotFoundException ex) { throw new ApplicationContextException( "Failed to load custom context class [" + contextClassName + "]", ex); } } else { contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName()); try { return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader()); } catch (ClassNotFoundException ex) { throw new ApplicationContextException( "Failed to load default context class [" + contextClassName + "]", ex); } } }
spring-web工程下，resource资源目录下
ContextLoader.properties
# Default WebApplicationContext implementation class for ContextLoader. # Used as fallback when no explicit context implementation has been specified as context-param. # Not meant to be customized by application developers. org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext
默认的WebApplicationContext为XmlWebApplicationContext
private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties"; private static final Properties defaultStrategies; static { // Load default strategy implementations from properties file. // This is currently strictly internal and not meant to be customized // by application developers. try { ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class); defaultStrategies = PropertiesLoaderUtils.loadProperties(resource); } catch (IOException ex) { throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage()); } }
到此为止，WebApplicationContext（XmlWebApplicationContext）创建完毕。