SpringMVC的实现与Web环境
2019-04-17 本文已影响0人
appreciate_2018
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IOC容器在web环境初始化过程
SpringMVC是建立在IOC容器的基础上的,SpringIOC是一个独立的模块,需要在web环境中引入SpringIOC并启动。通常我们会在web.xml配置。
<servlet>
<servlet-name>spring</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>spring</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath*:applicationContext.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
DispatcherServlet:Springmvc的前端控制器:初始化mvc组件与分发请求。
ContextLoaderListener：负责监听IOC容器在web环境初始化的整个过程。
context-param：SpringIOC读取bean的路径。
ContextLoaderListener创建的上下文为根上下文,同时还有一个输入MVC的子上下文。
public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
public ContextLoaderListener() {
}
public ContextLoaderListener(WebApplicationContext context) {
super(context);
}
public void contextInitialized(ServletContextEvent event) {
this.initWebApplicationContext(event.getServletContext());
}
public void contextDestroyed(ServletContextEvent event) {
this.closeWebApplicationContext(event.getServletContext());
ContextCleanupListener.cleanupAttributes(event.getServletContext());
}
}
ContextLoaderListener继承了ContextLoader并实现了ServletContextListener，这个监听器是启动根IOC容器并把它载入web容器的主要模块，首先从servlet事件中得到servletContext，然后可以读取配置在web.xml中的各个相关值，接着Contextloader会实例化WebapplicationContext,并完成载入跟初始化过程，这个被初始化的上下文为根上下文。获取根上下文的方法:
WebApplicationContext w = WebApplicationContextUtils.getWebApplicationContext(ServletContext sc);
ServletContextListener是ServlettListener的监听者，当服务启动或结束时，会调用相对应的回调方法
public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
public ContextLoaderListener() {
}
public ContextLoaderListener(WebApplicationContext context) {
super(context);
}
public void contextInitialized(ServletContextEvent event) {
this.initWebApplicationContext(event.getServletContext());
}
public void contextDestroyed(ServletContextEvent event) {
this.closeWebApplicationContext(event.getServletContext());
ContextCleanupListener.cleanupAttributes(event.getServletContext());
}
}
在initWebApplicationContext中,根上下文创建成功时，会存在web容器的ServletContext中供需要时使用。而当根上下文创建好时，Web容器开始初始化DispatcherServlet，DispatcherServlet会建立自己当上下文来持有SpringMVC的bean对象。
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DispatcherServlet的初始化过程
DispatcherServlet的继承关系（引用spring技术内幕）.png
DispatcherServlet的处理过程（引用spring技术内幕）.png
通过时序图可看到DispatcherServlet初始化是在httpServletBean完成的
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
//从初始化参数，配置bean属性
try {
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
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) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
throw ex;
}
//调用子类来初始化bean
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis();
try {
//初始化web上下文
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
catch (RuntimeException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
if (this.logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}
protected WebApplicationContext initWebApplicationContext() {
//获取根上下文
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) {
//使用根上下文为mvc上下文的双亲上下文
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
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
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.
onRefresh(wac);
}
if (this.publishContext) {
// 把当前上下文放到servletContext中
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}
springMVC的上下文则是在initFrameworkServlet()初始化的,主要是将根上下文传递给它，然后利用反射来实例化上下文对象。最终调用IOC容器的refresh()方法来完成容器的初始化。
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DispatcherServlet具体做了什么事？
由上面的时序图中可看到在DispatcherServlet中,主要做了两件事：
1.initStrategies():初始化MVC。
2.doDispatch():对http请求进行分发。
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
主要对initHandlerMapping初始化进行分析,HandlerMapping主要是为http请求找到相对应的Controller控制器，在initHandlerMappings中把bean配置文件中配置好的HandlerMapping载入到IOC容器中。
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
// 从所有的上下文中获取HandlerMapping
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
//保存HandlerMapping到list中
this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
//对HandlerMapping并排序
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
//从上下文信息里根据handler名称来获取HandlerMapping
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.
}
}
//通过注册确保我们至少有一个HandlerMapping
//如果未找到其他映射，则为默认的HandlerMapping。
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isDebugEnabled()) {
logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
}
}
}
HandlerMapping接口主要维护着handler跟url的映射关系，我们来分析下HandlerMapping的主要实现。
public interface HandlerMapping {
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}
HandlerMapping里只有一个方法getHandler(),这个方法返回了一个HandlerExecutionChain，这个HandlerExecutionChain持有一个拦截器链跟handler，通过拦截器链来对handler进行增强功能。HandlerExecutionChain里定义对handler跟interceptors需要在定义HandlerMapping时配置好，那么我们来分析一下这个注册的过程。
@Override
public void initApplicationContext() throws BeansException {
super.initApplicationContext();
registerHandlers(this.urlMap);
}
protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
if (urlMap.isEmpty()) {
logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
}
else {
for (Map.Entry<String, Object> entry : urlMap.entrySet()) {
String url = entry.getKey();
Object handler = entry.getValue();
// Prepend with slash if not already present.
if (!url.startsWith("/")) {
url = "/" + url;
}
// Remove whitespace from handler bean name.
if (handler instanceof String) {
handler = ((String) handler).trim();
}
//调用基类来完成注册
registerHandler(url, handler);
}
}
}
具体的注册是在基类AbstractUrlHandlerMapping里完成的
protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
Assert.notNull(urlPath, "URL path must not be null");
Assert.notNull(handler, "Handler object must not be null");
Object resolvedHandler = handler;
// 如果是用bean名称定义，那么直接从容器中获取
if (!this.lazyInitHandlers && handler instanceof String) {
String handlerName = (String) handler;
if (getApplicationContext().isSingleton(handlerName)) {
resolvedHandler = getApplicationContext().getBean(handlerName);
}
}
Object mappedHandler = this.handlerMap.get(urlPath);
if (mappedHandler != null) {
if (mappedHandler != resolvedHandler) {
throw new IllegalStateException(
"Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
"]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
}
}
else {
if (urlPath.equals("/")) {
if (logger.isInfoEnabled()) {
logger.info("Root mapping to " + getHandlerDescription(handler));
}
setRootHandler(resolvedHandler);
}
else if (urlPath.equals("/*")) {
if (logger.isInfoEnabled()) {
logger.info("Default mapping to " + getHandlerDescription(handler));
}
setDefaultHandler(resolvedHandler);
}
else {
//将url跟controller设置到handlerMap中
this.handlerMap.put(urlPath, resolvedHandler);
if (logger.isInfoEnabled()) {
logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
}
}
}
}
//存放url跟controller
private final Map<String, Object> handlerMap = new LinkedHashMap<String, Object>();
这个时候已经为SpringMVC分发http请求准备好了基础数据,根据handlerMap中的url映射到具体的handler，我们来看一下HandlerMapping是如何完成请求映射的。是如何找到handler的。
Override
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
//具体实现在AbstractUrlHandlerMapping类的getHandlerInternal()里面,
@Override
protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
//从request中获取url
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
//将url跟handler进行匹配
Object handler = lookupHandler(lookupPath, request);
if (handler == null) {
// We need to care for the default handler directly, since we need to
// expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
Object rawHandler = null;
if ("/".equals(lookupPath)) {
rawHandler = getRootHandler();
}
if (rawHandler == null) {
rawHandler = getDefaultHandler();
}
if (rawHandler != null) {
// Bean name or resolved handler?
if (rawHandler instanceof String) {
String handlerName = (String) rawHandler;
rawHandler = getApplicationContext().getBean(handlerName);
}
validateHandler(rawHandler, request);
handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
}
}
if (handler != null && logger.isDebugEnabled()) {
logger.debug("Mapping [" + lookupPath + "] to " + handler);
}
else if (handler == null && logger.isTraceEnabled()) {
logger.trace("No handler mapping found for [" + lookupPath + "]");
}
return handler;
}
protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
// Direct match?
Object handler = this.handlerMap.get(urlPath);
if (handler != null) {
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
return buildPathExposingHandler(handler, urlPath, urlPath, null);
}
// Pattern match?
List<String> matchingPatterns = new ArrayList<String>();
for (String registeredPattern : this.handlerMap.keySet()) {
if (getPathMatcher().match(registeredPattern, urlPath)) {
matchingPatterns.add(registeredPattern);
}
else if (useTrailingSlashMatch()) {
if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) {
matchingPatterns.add(registeredPattern +"/");
}
}
}
String bestPatternMatch = null;
Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
if (!matchingPatterns.isEmpty()) {
Collections.sort(matchingPatterns, patternComparator);
if (logger.isDebugEnabled()) {
logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
}
bestPatternMatch = matchingPatterns.get(0);
}
if (bestPatternMatch != null) {
handler = this.handlerMap.get(bestPatternMatch);
if (handler == null) {
Assert.isTrue(bestPatternMatch.endsWith("/"));
handler = this.handlerMap.get(bestPatternMatch.substring(0, bestPatternMatch.length() - 1));
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath);
// There might be multiple 'best patterns', let's make sure we have the correct URI template variables
// for all of them
Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();
for (String matchingPattern : matchingPatterns) {
if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) {
Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
uriTemplateVariables.putAll(decodedVars);
}
}
if (logger.isDebugEnabled()) {
logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
}
return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables);
}
// No handler found...
return null;
}
具体的http分发是由dispatcherServlet的doDispatch()来做的,我们直接看代码
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
//先设置视图模型
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 根据请求获取Handler.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 利用HandlerAdapter检查handler的合法性
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 真正完成handler的调用
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
springMVC的流程（图片引用spring技术内幕）
