Spring 学习第一天

1、web.xml 配置

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

2、tomcat 启动后会进行listener加载初始化

/**
* Initialize the root web application context.
*/
public void contextInitialized(ServletContextEvent event) {
//createContextLoader 已经作废
this.contextLoader = createContextLoader();
//如果 contextLoader 是null 把当前对象给它 此处判断可以直接去掉
if (this.contextLoader == null) {
this.contextLoader = this;
}
//开始初始化 WebApplicationContext
this.contextLoader.initWebApplicationContext(event.getServletContext());
}

3、initWebApplicationContext 方法负责初始化 Context

/**
* Initialize Spring's web application context for the given servlet context,
* using the application context provided at construction time, or creating a new one
* according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and
* "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.
* @param servletContext current servlet context
* @return the new WebApplicationContext
* @see #ContextLoader(WebApplicationContext)
* @see #CONTEXT_CLASS_PARAM
* @see #CONFIG_LOCATION_PARAM
*/
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
//String ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE = WebApplicationContext.class.getName() + ".ROOT";
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
//上面的判断条件不为空则证明容器中已经有一个 根节点为。root的属性 说明初始化过来所以会抛出异常
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) {
// 此处创建context
this.context = createWebApplicationContext(servletContext);
}

if (this.context instanceof ConfigurableWebApplicationContext) {
// 如果context是 ConfigurableWebApplicationContext类型的 则直接把 context强制转换
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
// 判断cwac 是否Active
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) {
// cwac 的父属性如果为null 则找到他的父亲并给给父属性赋值
// 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);
}
// 此处是比较重点的一个方法  先学习该方法 下面的内容以后再看 先把代码给省略的一部分
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
//以下部分先不学习
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;
}
}

4、先看下configureAndRefreshWebApplicationContext方法 主要是配置和刷新 context

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
//这是个protected属性的方法
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
//public static final String CONTEXT_ID_PARAM = "contextId";
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
//String APPLICATION_CONTEXT_ID_PREFIX = WebApplicationContext.class.getName() + ":";
if (sc.getMajorVersion() == 2 && sc.getMinorVersion() < 5) {
// Servlet <= 2.4: resort to name specified in web.xml, if any.
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getServletContextName()));
}
else {

wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
}
// 给ServletContext赋值
wac.setServletContext(sc);
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);
}
// 用于自定义ContextLoader时，扩充自定义Context
customizeContext(sc, wac);
// 完成context构造过程。 重新刷新容器
wac.refresh();
}

转载于:https://www.geek-share.com/detail/2675105705.html