spring容器监听器

Posted 2020-10-08 BINGJJFLY

web.xml配置文件

<context-param>
　　<param-name>contextConfigLocation</param-name>
　　<param-value>
　　　　classpath:spring/spring-*.xml
　　</param-value>
</context-param>

<listener>
　　<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

ContextLoaderListener上下文加载监听器

　　
　　/**
　　 * servlet容器创建时创建spring容器
　　 */
　　@Override
    public void contextInitialized(ServletContextEvent event) {
        initWebApplicationContext(event.getServletContext());
    }


    /**
     * servlet容器销毁时注销spring容器
     */
    @Override
    public void contextDestroyed(ServletContextEvent event) {
        closeWebApplicationContext(event.getServletContext());
        ContextCleanupListener.cleanupAttributes(event.getServletContext());
    }

创建spring容器

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");
        }
        long startTime = System.currentTimeMillis();

        try {// 创建上下文，后文详解#1
            if (this.context == null) {
                this.context = createWebApplicationContext(servletContext);
            }
            if (this.context instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
                if (!cwac.isActive()) {
                    if (cwac.getParent() == null) {
                        ApplicationContext parent = loadParentContext(servletContext);
                        cwac.setParent(parent);
                    }
　　　　　　　　　　　　// 刷新上下文包括解析、注册、实例化bean等，后文详解#2
                    configureAndRefreshWebApplicationContext(cwac, servletContext);
                }
            }
　　　　　　　// 将创建好的上下文放到application作用域中
            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;
        }
    }

书接前文#1

protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
　　　　　// 获得具体的上下文类即XmlWebApplicationContext
        Class<?> contextClass = determineContextClass(sc);
        if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
            throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
                    "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
        }
　　　　　// 实例化XmlWebApplicationContext对象，构造函数反射
        return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    }

书接前文#2

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
        if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
            String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
            if (idParam != null) {
                wac.setId(idParam);
            }
            else {
                wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
                        ObjectUtils.getDisplayString(sc.getContextPath()));
            }
        }

        wac.setServletContext(sc);
　　　　　// 获得<context-param>标签中的内容
        String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
        if (configLocationParam != null) {
            wac.setConfigLocation(configLocationParam);
        }

        ConfigurableEnvironment env = wac.getEnvironment();
        if (env instanceof ConfigurableWebEnvironment) {
            ((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
        }
　　　　  // 检查有没有自定义的上下文
        customizeContext(sc, wac);
　　　　 // 刷新上下文
        wac.refresh();
    }

接下来是销毁spring容器

public void closeWebApplicationContext(ServletContext servletContext) {
        servletContext.log("Closing Spring root WebApplicationContext");
        try {
            if (this.context instanceof ConfigurableWebApplicationContext) {
　　　　　　　　　　// 这里包括广播shutdown事件，销毁bean，销毁BeanFactory等
                ((ConfigurableWebApplicationContext) this.context).close();
            }
        }
        finally {
            ClassLoader ccl = Thread.currentThread().getContextClassLoader();
            if (ccl == ContextLoader.class.getClassLoader()) {
                currentContext = null;
            }
            else if (ccl != null) {
                currentContextPerThread.remove(ccl);
            }
　　　　　　　 // application作用域中去除上下文
            servletContext.removeAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
            if (this.parentContextRef != null) {
                this.parentContextRef.release();
            }
        }
    }

static void cleanupAttributes(ServletContext sc) {
        Enumeration<String> attrNames = sc.getAttributeNames();
        while (attrNames.hasMoreElements()) {
            String attrName = attrNames.nextElement();
            if (attrName.startsWith("org.springframework.")) {
                Object attrValue = sc.getAttribute(attrName);
　　　　　　　　　 // 对于实现了DisposableBean接口的bean，容器销毁时执行destroy方法
                if (attrValue instanceof DisposableBean) {
                    try {
                        ((DisposableBean) attrValue).destroy();
                    }
                    catch (Throwable ex) {
                        logger.error("Couldn\'t invoke destroy method of attribute with name \'" + attrName + "\'", ex);
                    }
                }
            }
        }
    }