Spring源码分析

在Java EE项目中，Spring的载入时通过监听器实现的，无论是在SSH还是SSM，在web.xml都会有这样的配置

<!-- 载入spring配置 --><context-param><param-name>contextConfigLocation</param-name><param-value>classpath*:cn/resources/applicationContext.xml        </param-value></context-param><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener>

进入ContextLoaderListener这个类

 public class ContextLoaderListener/*     */   extends ContextLoader/*     */   implements ServletContextListener/*     */ {/*     */   public ContextLoaderListener() {}/*     */   /*     */   public ContextLoaderListener(WebApplicationContext context)/*     */   {/*  98 */     super(context);/*     */   }/*     */   /*     */ /*     */ /*     */ /*     */ /*     */   public void contextInitialized(ServletContextEvent event)/*     */   {/* 107 */     initWebApplicationContext(event.getServletContext());/*     */   }/*     */   /*     */ /*     */ /*     */ /*     */ /*     */   public void contextDestroyed(ServletContextEvent event)/*     */   {/* 116 */     closeWebApplicationContext(event.getServletContext());/* 117 */     ContextCleanupListener.cleanupAttributes(event.getServletContext());/*     */   }/*     */ }

contextInitialized与contextDestroyed分别对应着初始化与销毁，我们来看看初始化

public WebApplicationContext initWebApplicationContext(ServletContext servletContext)/*     */   {/* 296 */     if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {/* 297 */       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!");/*     */     }/*     */     /*     */ /*     */ /* 302 */     Log logger = LogFactory.getLog(ContextLoader.class);/* 303 */     servletContext.log("Initializing Spring root WebApplicationContext");/* 304 */     if (logger.isInfoEnabled()) {/* 305 */       logger.info("Root WebApplicationContext: initialization started");/*     */     }/* 307 */     long startTime = System.currentTimeMillis();/*     */     /*     */ /*     */     try/*     */     {/* 312 */       if (this.context == null) {/* 313 */         this.context = createWebApplicationContext(servletContext);/*     */       }/* 315 */       if ((this.context instanceof ConfigurableWebApplicationContext)) {/* 316 */         ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)this.context;/* 317 */         if (!cwac.isActive())/*     */         {/*     */ /* 320 */           if (cwac.getParent() == null)/*     */           {/*     */ /* 323 */             ApplicationContext parent = loadParentContext(servletContext);/* 324 */             cwac.setParent(parent);/*     */           }/* 326 */           configureAndRefreshWebApplicationContext(cwac, servletContext);/*     */         }/*     */       }/* 329 */       servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);/*     */       /* 331 */       ClassLoader ccl = Thread.currentThread().getContextClassLoader();/* 332 */       if (ccl == ContextLoader.class.getClassLoader()) {/* 333 */         currentContext = this.context;/*     */       }/* 335 */       else if (ccl != null) {/* 336 */         currentContextPerThread.put(ccl, this.context);/*     */       }/*     */       /* 339 */       if (logger.isDebugEnabled()) {/* 340 */         logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");/*     */       }/*     */       /* 343 */       if (logger.isInfoEnabled()) {/* 344 */         long elapsedTime = System.currentTimeMillis() - startTime;/* 345 */         logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");/*     */       }/*     */       /* 348 */       return this.context;/*     */     }/*     */     catch (RuntimeException ex) {/* 351 */       logger.error("Context initialization failed", ex);/* 352 */       servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);/* 353 */       throw ex;/*     */     }/*     */     catch (Error err) {/* 356 */       logger.error("Context initialization failed", err);/* 357 */       servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);/* 358 */       throw err;/*     */     }/*     */   }