昨天讲到DispatcherServlet因为继承了FrameworkServlet、HttpServletBean、HttpServlet,因此可以通过Servlet的API对请求进行一些处理与响应。
DispatcherServlet的初始化在ContextLoaderListener完成对根上下文的初始化之后才会执行。
具体的初始化时间取决于web.xml中servlet关于load-on-startup的配置。
当load-on-startup为负数或者没有配置时,在第一次request请求时加载;
当load-on-startup不为负数时,代表DispatcherServlet在ContextLoaderListener完成根上下文的初始化之后即加载。
下面来看DispatcherServlet具体的初始化源码:
HttpServletBean重写了其父类HttpServlet的init方法:
public final void init() throws ServletException {
// Set bean properties from init parameters.
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
// Let subclasses do whatever initialization they like.
initServletBean();
}
HttpServletBean的init方法,读取Servlet的初始化参数,然后调用initServletBean来初始化Servlet的Bean对象。
这个initServletBean是一个钩子方法,由子类去实现。
在这里调用到子类
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
if (logger.isInfoEnabled()) {
logger.info("Initializing Servlet '" + getServletName() + "'");
}
long startTime = System.currentTimeMillis();
try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
logger.error("Context initialization failed", ex);
throw ex;
}
if (logger.isDebugEnabled()) {
String value = this.enableLoggingRequestDetails ?
"shown which may lead to unsafe logging of potentially sensitive data" :
"masked to prevent unsafe logging of potentially sensitive data";
logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
"': request parameters and headers will be " + value);
}
if (logger.isInfoEnabled()) {
logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
}
}
initServletBean中实现了DispatcherServlet中上下文的实现,设置上下文的根上下文,并使ServletContext持有这个DispatcherServlet上下文。
initWebApplicationContext中的onRefresh()方式用来在初始化spring mvc需要的bean
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
/**
* Initialize the strategy objects that this servlet uses.
* <p>May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
//这里配置path 与 handler ,也是什么请求,走什么样的处理器
//而处理器,是一系列拦截器+Controller组成
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}