前言
在创建容器过程中或当请求来的时候，容器会调用一次DispatcherServlet的init方法，init只会被调用一次。
一、执行时机
容器在创建过程中初始化，会执行createServlet( )
public void createServlet() throws ServletException {
if (permanentlyUnavailable) {
return;
}
try {
//这里校验LoadOnStartup参数
if (!started && servletInfo.getLoadOnStartup() != null && servletInfo.getLoadOnStartup() >= 0) {
//这里执行初始化
instanceStrategy.start();
started = true;
}
} catch (UnavailableException e) {
if (e.isPermanent()) {
permanentlyUnavailable = true;
stop();
}
}
}
在WebMvcProperties的内部类Servlet中的定义，默认值是-1，DispatcherServlet会在请求来时执行一次初始化
private int loadOnStartup = -1;
因此要想在创建容器的过程中初始化DispatcherServlet，这需要设置该参数的值大于等于0。
spring.mvc.servlet.load-on-startup=1
二、执行流程
1、首先进入GenericServlet的init( )
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
2、进入HttpServletBean的init( )
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();
}
3、进入FrameworkServlet的initServletBean( )
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 {
//初始化WebApplicationContext
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");
}
}
4、initWebApplicationContext( )
protected WebApplicationContext initWebApplicationContext() {
//获取WebApplicationContext
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
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) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
//不存在时查找
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
//不存在时创建
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
synchronized (this.onRefreshMonitor) {
//刷新
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
5、进入DispatcherServlet的onRefresh( )
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
6、initStrategies(context)
初始化9种策略
protected void initStrategies(ApplicationContext context) {
//文件上传相关
initMultipartResolver(context);
//本地化语言相关
initLocaleResolver(context);
//主题相关
initThemeResolver(context);
//处理器映射器相关
initHandlerMappings(context);
//处理器适配器相关
initHandlerAdapters(context);
//处理器异常处理相关
initHandlerExceptionResolvers(context);
//请求到视图名翻译相关
initRequestToViewNameTranslator(context);
//视图解析器相关
initViewResolvers(context);
//FlashMap相关
initFlashMapManager(context);
}
三、策略初始化
1、initMultipartResolver(context)
private void initMultipartResolver(ApplicationContext context) {
try {
//从spring容器中获取
this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
if (logger.isDebugEnabled()) {
logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");
}
}
catch (NoSuchBeanDefinitionException ex) {
// Default is no multipart resolver.
//不存在时设置为null，不支持文件上传请求
this.multipartResolver = null;
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +
"': no multipart request handling provided");
}
}
}
2、initLocaleResolver(context)
private void initLocaleResolver(ApplicationContext context) {
try {
//从spring容器中获取
this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);
if (logger.isDebugEnabled()) {
logger.debug("Using LocaleResolver [" + this.localeResolver + "]");
}
}
catch (NoSuchBeanDefinitionException ex) {
// We need to use the default.
//获取默认的
this.localeResolver = getDefaultStrategy(context, LocaleResolver.class);
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate LocaleResolver with name '" + LOCALE_RESOLVER_BEAN_NAME +
"': using default [" + this.localeResolver + "]");
}
}
}
protected <T> T getDefaultStrategy(ApplicationContext context, Class<T> strategyInterface) {
List<T> strategies = getDefaultStrategies(context, strategyInterface);
//只能有一个
if (strategies.size() != 1) {
throw new BeanInitializationException(
"DispatcherServlet needs exactly 1 strategy for interface [" + strategyInterface.getName() + "]");
}
return strategies.get(0);
}
protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
String key = strategyInterface.getName();
//从缓存中获取
String value = defaultStrategies.getProperty(key);
if (value != null) {
String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
List<T> strategies = new ArrayList<>(classNames.length);
for (String className : classNames) {
try {
Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
//创建bean
Object strategy = createDefaultStrategy(context, clazz);
strategies.add((T) strategy);
}
catch (ClassNotFoundException ex) {
throw new BeanInitializationException(
"Could not find DispatcherServlet's default strategy class [" + className +
"] for interface [" + key + "]", ex);
}
catch (LinkageError err) {
throw new BeanInitializationException(
"Unresolvable class definition for DispatcherServlet's default strategy class [" +
className + "] for interface [" + key + "]", err);
}
}
return strategies;
}
else {
return new LinkedList<>();
}
}
defaultStrategies，是从DispatcherServlet.properties配置文件中读取的
private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
用同样的方式初始化ThemeResolver、RequestToViewNameTranslator、FlashMapManager策略组件。
3、initHandlerMappings(context)
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
//是否去检测所有的HandlerMapping
if (this.detectAllHandlerMappings) {
// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
//从spring容器中获取所有的HandlerMapping
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<>(matchingBeans.values());
// We keep HandlerMappings in sorted order.
//根据@Order进行排序
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
//只用名称为handlerMapping的bean
HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerMapping later.
}
}
// Ensure we have at least one HandlerMapping, by registering
// a default HandlerMapping if no other mappings are found.
if (this.handlerMappings == null) {
//没有找到handlerMapping，则使用DispatcherServlet.properties缺省的配置
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isDebugEnabled()) {
logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
}
}
}
用同样的方式初始化 HandlerAdapter、HandlerExceptionResolver、ViewResolver策略组件
四、DispatcherServlet.properties
缺省的8个策略组件都是在这个文件中配置的
# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.
org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver
org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver
org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver
org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver
org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager