spring有三种启动方式,使用ContextLoaderServlet,ContextLoaderListener和ContextLoaderPlugIn.

港控/mmm° 2022-08-27 12:51 108阅读 0赞

spring有三种启动方式,使用ContextLoaderServlet,ContextLoaderListener和ContextLoaderPlugIn.  
看一下ContextLoaderListener的源码,这是一个ServletContextListener  
/\*\*  
  \* Initialize the root web application context.  
  \*/  
 public void contextInitialized(ServletContextEvent event) \{  
  this.contextLoader = createContextLoader();  
  this.contextLoader.initWebApplicationContext(event.getServletContext());  
 \}  
   
  /\*\*  
  \* Create the ContextLoader to use. Can be overridden in subclasses.  
  \* @return the new ContextLoader  
  \*/  
 protected ContextLoader createContextLoader() \{  
  return new ContextLoader();  
 \}

contextLoader的源码  
 public WebApplicationContext initWebApplicationContext(ServletContext servletContext)  
   throws BeansException \{

long startTime = System.currentTimeMillis();  
  if (logger.isInfoEnabled()) \{  
   logger.info("Root WebApplicationContext: initialization started");  
  \}  
  servletContext.log("Loading Spring root WebApplicationContext");

try \{  
   // Determine parent for root web application context, if any.  
   ApplicationContext parent = loadParentContext(servletContext);

WebApplicationContext wac = createWebApplicationContext(servletContext, parent);  
   servletContext.setAttribute(  
     WebApplicationContext.ROOT\_WEB\_APPLICATION\_CONTEXT\_ATTRIBUTE, wac);

if (logger.isInfoEnabled()) \{  
    logger.info("Using context class \[" + wac.getClass().getName() +  
      "\] for root WebApplicationContext");  
   \}  
   if (logger.isDebugEnabled()) \{  
    logger.debug("Published root WebApplicationContext \[" + wac +  
      "\] 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 wac;  
  \}  
  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;  
  \}  
 \}  
 注意WebApplicationContext.ROOT\_WEB\_APPLICATION\_CONTEXT\_ATTRIBUTE,这里面放了WebApplicationContext,需要使用时从ServletContext取出  
 可以使用WebApplicationContextUtils得到WebApplicationContext  
 public static WebApplicationContext getWebApplicationContext(ServletContext sc) \{  
  Object attr = sc.getAttribute(WebApplicationContext.ROOT\_WEB\_APPLICATION\_CONTEXT\_ATTRIBUTE);  
  if (attr == null) \{  
   return null;  
  \}  
  if (attr instanceof RuntimeException) \{  
   throw (RuntimeException) attr;  
  \}  
  if (attr instanceof Error) \{  
   throw (Error) attr;  
  \}  
  if (!(attr instanceof WebApplicationContext)) \{  
   throw new IllegalStateException("Root context attribute is not of type WebApplicationContext: " + attr);  
  \}  
  return (WebApplicationContext) attr;  
 \}  
 关键的问题在于struts如何启动的spring的,ContextLoaderPlugIn的源码  
   
 // Publish the context as a servlet context attribute.  
  String attrName = getServletContextAttributeName();  
  getServletContext().setAttribute(attrName, wac);  
   
 public String getServletContextAttributeName() \{  
  return SERVLET\_CONTEXT\_PREFIX + getModulePrefix();  
 \}  
 不同加载的Key竟然不同,原因就是WebApplicationContext放在那里的问题,可spring调用的时候会根据WebApplicationContext里面定义的那个名字去找的,问题出在这里

在struts-config.xml中配置  
    <plug-in className="org.springframework.web.struts.ContextLoaderPlugIn">  
      <set-property property="contextConfigLocation" value="/WEB-INF/applicationContext.xml" />  
    </plug-in>

原理是这样的,Struts虽然只能有一个ActionServlet实例,但是对于不同的子应用分别能有自己的RequestProcessor实例每个RequestProcessor实例分别对应不同的struts配置文件。  
   子应用的ProcessorClass类必须重写一般就是继承RequestProcessor类，然后再其配置文件的controller元素中的<processorClass>属性中作出修改。那么当  
  getRequestProcessor(getModuleConfig(request)).process(request,response);就能根据request选择相应的moduleconfig,再根据其<processorClass>属性选择相应的RequestProcessor子类来处理相应的请求了。