目的: 主要是瞭解配置文件方式的父子容器創建
入口:
ContextLoaderListener.java
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
在進入這個入口之前,我們看看ContextLoaderListener實現了ServletContextListener接口
ServletContextListener.java
public interface ServletContextListener extends java.util.EventListener {
void contextInitialized(javax.servlet.ServletContextEvent servletContextEvent);
void contextDestroyed(javax.servlet.ServletContextEvent servletContextEvent);
}
方法調用鏈: StandardContext.startInternal()->listenerStart()->ServletContextListener.contextInitialized()
,本人之前寫過Tomcat源碼分析-啓動start過程,裏面粗略講述了start過程。
回到之前提到的入口
initWebApplicationContext(event.getServletContext());
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
//從一行代碼便可以看出,初始化容器之後會放入servletContext之中。
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");
}
long startTime = System.currentTimeMillis();
try {
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
if (this.context == null) {
//通過策略獲取具體創建的context類型並且反射創建
this.context = createWebApplicationContext(servletContext);
}
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);
}
//配置並且刷新容器
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");
}
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;
}
}
createWebApplicationContext(servletContext)
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);
}
configureAndRefreshWebApplicationContext(cwac, servletContext)
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
wac.setServletContext(sc);
//取出contextConfigLocation對應的參數作爲配置文件
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
customizeContext(sc, wac);
wac.refresh();
}
入口
方法調用鏈
HttpServletBean.init()->FrameworkServlet.initServletBean()->FrameworkServlet.initWebApplicationContext()
initWebApplicationContext()有一些細節還沒弄明白。
protected WebApplicationContext initWebApplicationContext() {
//重點,這裏把之前放進去的WebApplicationContext 取出來了。
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
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) {
// 設置父容器
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// 從context 中取
wac = findWebApplicationContext();
}
if (wac == null) {
// 創建一個新的
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac);
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}
由於在上面的initWebApplicationContext()方法中,Springboot的容器已經傳入並且是webApplicationContext類型的 ,所以不需要再創建一個MVC容器。所以只有一個容器,沒有父子容器的概念了。
在調試代碼發現了一系列的xxxInitializer,從網上找了下文章瞭解了它的作用。發現主要就是通過xxxInitializer擴展context,避免使用web.xml.
StandardContext類的startInternal()方法中的如下片段。
// Call ServletContainerInitializers
for (Map.Entry<ServletContainerInitializer, Set<Class<?>>> entry :
initializers.entrySet()) {
try {
entry.getKey().onStartup(entry.getValue(),
getServletContext());
} catch (ServletException e) {
log.error(sm.getString("standardContext.sciFail"), e);
ok = false;
break;
}
}
這其中還有一個SPI機制,大家有興趣可以去了解一下
