本文介绍: SpringMVC中的拦截器用于拦截控制器方法的执行SpringMVC中的拦截器需要实现HandlerInterceptorSpringMVC的拦截器必须在SpringMVC的配置文件中进行配置：</</</</
十、拦截器
1、拦截器的配置
SpringMVC中的拦截器用于拦截控制器方法的执行
SpringMVC中的拦截器需要实现HandlerInterceptor
SpringMVC的拦截器必须在SpringMVC的配置文件中进行配置：
<bean class="com.atguigu.interceptor.FirstInterceptor"></bean>
<ref bean="firstInterceptor"></ref>
<!-- 以上两种配置方式都是对DispatcherServlet所处理的所有的请求进行拦截 -->
<mvc:interceptor>
<mvc:mapping path="/**"/>
<mvc:exclude-mapping path="/testRequestEntity"/>
<ref bean="firstInterceptor"></ref>
</mvc:interceptor>
<!--
以上配置方式可以通过ref或bean标签设置拦截器，通过mvc:mapping设置需要拦截的请求，通过mvc:exclude-mapping设置需要排除的请求，即不需要拦截的请求
-->
2、拦截器的三个抽象方法
SpringMVC中的拦截器有三个抽象方法：
preHandle：控制器方法执行之前执行preHandle()，其boolean类型的返回值表示是否拦截或放行，返回true为放行，即调用控制器方法；返回false表示拦截，即不调用控制器方法
postHandle：控制器方法执行之后执行postHandle()
afterComplation：处理完视图和模型数据，渲染视图完毕之后执行afterComplation()
3、多个拦截器的执行顺序
a>若每个拦截器的preHandle()都返回true
此时多个拦截器的执行顺序和拦截器在SpringMVC的配置文件的配置顺序有关：
preHandle()会按照配置的顺序执行，而postHandle()和afterComplation()会按照配置的反序执行
b>若某个拦截器的preHandle()返回了false
preHandle()返回false和它之前的拦截器的preHandle()都会执行，postHandle()都不执行，返回false的拦截器之前的拦截器的afterComplation()会执行
十一、异常处理器
1、基于配置的异常处理
SpringMVC提供了一个处理控制器方法执行过程中所出现的异常的接口：HandlerExceptionResolver
HandlerExceptionResolver接口的实现类有：DefaultHandlerExceptionResolver和SimpleMappingExceptionResolver
SpringMVC提供了自定义的异常处理器SimpleMappingExceptionResolver，使用方式：
<bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
<property name="exceptionMappings">
<props>
<!--
properties的键表示处理器方法执行过程中出现的异常
properties的值表示若出现指定异常时，设置一个新的视图名称，跳转到指定页面
-->
<prop key="java.lang.ArithmeticException">error</prop>
</props>
</property>
<!--
exceptionAttribute属性设置一个属性名，将出现的异常信息在请求域中进行共享
-->
<property name="exceptionAttribute" value="ex"></property>
</bean>
2、基于注解的异常处理
//@ControllerAdvice将当前类标识为异常处理的组件
@ControllerAdvice
public class ExceptionController {
//@ExceptionHandler用于设置所标识方法处理的异常
@ExceptionHandler(ArithmeticException.class)
//ex表示当前请求处理中出现的异常对象
public String handleArithmeticException(Exception ex, Model model){
model.addAttribute("ex", ex);
return "error";
}
}
十二、注解配置SpringMVC
使用配置类和注解代替web.xml和SpringMVC配置文件的功能
1、创建初始化类，代替web.xml
在Servlet3.0环境中，容器会在类路径中查找实现javax.servlet.ServletContainerInitializer接口的类，如果找到的话就用它来配置Servlet容器。
Spring提供了这个接口的实现，名为SpringServletContainerInitializer，这个类反过来又会查找实现WebApplicationInitializer的类并将配置的任务交给它们来完成。Spring3.2引入了一个便利的WebApplicationInitializer基础实现，名为AbstractAnnotationConfigDispatcherServletInitializer，当我们的类扩展了AbstractAnnotationConfigDispatcherServletInitializer并将其部署到Servlet3.0容器的时候，容器会自动发现它，并用它来配置Servlet上下文。
public class WebInit extends AbstractAnnotationConfigDispatcherServletInitializer {
/**
* 指定spring的配置类
* @return
*/
@Override
protected Class<?>[] getRootConfigClasses() {
return new Class[]{SpringConfig.class};
}
/**
* 指定SpringMVC的配置类
* @return
*/
@Override
protected Class<?>[] getServletConfigClasses() {
return new Class[]{WebConfig.class};
}
/**
* 指定DispatcherServlet的映射规则，即url-pattern
* @return
*/
@Override
protected String[] getServletMappings() {
return new String[]{"/"};
}
/**
* 添加过滤器
* @return
*/
@Override
protected Filter[] getServletFilters() {
CharacterEncodingFilter encodingFilter = new CharacterEncodingFilter();
encodingFilter.setEncoding("UTF-8");
encodingFilter.setForceRequestEncoding(true);
HiddenHttpMethodFilter hiddenHttpMethodFilter = new HiddenHttpMethodFilter();
return new Filter[]{encodingFilter, hiddenHttpMethodFilter};
}
}
2、创建SpringConfig配置类，代替spring的配置文件
@Configuration
public class SpringConfig {
//ssm整合之后，spring的配置信息写在此类中
}
3、创建WebConfig配置类，代替SpringMVC的配置文件
@Configuration
//扫描组件
@ComponentScan("com.atguigu.mvc.controller")
//开启MVC注解驱动
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
//使用默认的servlet处理静态资源
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
configurer.enable();
}
//配置文件上传解析器
@Bean
public CommonsMultipartResolver multipartResolver(){
return new CommonsMultipartResolver();
}
//配置拦截器
@Override
public void addInterceptors(InterceptorRegistry registry) {
FirstInterceptor firstInterceptor = new FirstInterceptor();
registry.addInterceptor(firstInterceptor).addPathPatterns("/**");
}
//配置视图控制
/*@Override
public void addViewControllers(ViewControllerRegistry registry) {
registry.addViewController("/").setViewName("index");
}*/
//配置异常映射
/*@Override
public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
SimpleMappingExceptionResolver exceptionResolver = new SimpleMappingExceptionResolver();
Properties prop = new Properties();
prop.setProperty("java.lang.ArithmeticException", "error");
//设置异常映射
exceptionResolver.setExceptionMappings(prop);
//设置共享异常信息的键
exceptionResolver.setExceptionAttribute("ex");
resolvers.add(exceptionResolver);
}*/
//配置生成模板解析器
@Bean
public ITemplateResolver templateResolver() {
WebApplicationContext webApplicationContext = ContextLoader.getCurrentWebApplicationContext();
// ServletContextTemplateResolver需要一个ServletContext作为构造参数，可通过WebApplicationContext 的方法获得
ServletContextTemplateResolver templateResolver = new ServletContextTemplateResolver(
webApplicationContext.getServletContext());
templateResolver.setPrefix("/WEB-INF/templates/");
templateResolver.setSuffix(".html");
templateResolver.setCharacterEncoding("UTF-8");
templateResolver.setTemplateMode(TemplateMode.HTML);
return templateResolver;
}
//生成模板引擎并为模板引擎注入模板解析器
@Bean
public SpringTemplateEngine templateEngine(ITemplateResolver templateResolver) {
SpringTemplateEngine templateEngine = new SpringTemplateEngine();
templateEngine.setTemplateResolver(templateResolver);
return templateEngine;
}
//生成视图解析器并未解析器注入模板引擎
@Bean
public ViewResolver viewResolver(SpringTemplateEngine templateEngine) {
ThymeleafViewResolver viewResolver = new ThymeleafViewResolver();
viewResolver.setCharacterEncoding("UTF-8");
viewResolver.setTemplateEngine(templateEngine);
return viewResolver;
}
}
4、测试功能
@RequestMapping("/")
public String index(){
return "index";
}
十三、SpringMVC执行流程
1、SpringMVC常用组件
- DispatcherServlet：前端控制器，不需要工程师开发，由框架提供
作用：统一处理请求和响应，整个流程控制的中心，由它调用其它组件处理用户的请求
- HandlerMapping：处理器映射器，不需要工程师开发，由框架提供
作用：根据请求的url、method等信息查找Handler，即控制器方法
- Handler：处理器，需要工程师开发
作用：在DispatcherServlet的控制下Handler对具体的用户请求进行处理
- HandlerAdapter：处理器适配器，不需要工程师开发，由框架提供
作用：通过HandlerAdapter对处理器（控制器方法）进行执行
- ViewResolver：视图解析器，不需要工程师开发，由框架提供
作用：进行视图解析，得到相应的视图，例如：ThymeleafView、InternalResourceView、RedirectView
- View：视图
作用：将模型数据通过页面展示给用户
2、DispatcherServlet初始化过程
DispatcherServlet 本质上是一个 Servlet，所以天然的遵循 Servlet 的生命周期。所以宏观上是 Servlet 生命周期来进行调度。
a>初始化WebApplicationContext
所在类：org.springframework.web.servlet.FrameworkServlet
protected WebApplicationContext initWebApplicationContext() {
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
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
// 创建WebApplicationContext
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WebApplicationContext
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
// 将IOC容器在应用域共享
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
b>创建WebApplicationContext
所在类：org.springframework.web.servlet.FrameworkServlet
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
Class<?> contextClass = getContextClass();
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
// 通过反射创建 IOC 容器对象
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
// 设置父容器
wac.setParent(parent);
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
configureAndRefreshWebApplicationContext(wac);
return wac;
}
c>DispatcherServlet初始化策略
FrameworkServlet创建WebApplicationContext后，刷新容器，调用onRefresh(wac)，此方法在DispatcherServlet中进行了重写，调用了initStrategies(context)方法，初始化策略，即初始化DispatcherServlet的各个组件
所在类：org.springframework.web.servlet.DispatcherServlet
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
3、DispatcherServlet调用组件处理请求
a>processRequest()
FrameworkServlet重写HttpServlet中的service()和doXxx()，这些方法中调用了processRequest(request, response)
所在类：org.springframework.web.servlet.FrameworkServlet
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = buildLocaleContext(request);
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
initContextHolders(request, localeContext, requestAttributes);
try {
// 执行服务，doService()是一个抽象方法，在DispatcherServlet中进行了重写
doService(request, response);
}
catch (ServletException | IOException ex) {
failureCause = ex;
throw ex;
}
catch (Throwable ex) {
failureCause = ex;
throw new NestedServletException("Request processing failed", ex);
}
finally {
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
logResult(request, response, failureCause, asyncManager);
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
b>doService()
所在类：org.springframework.web.servlet.DispatcherServlet
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
logRequest(request);
// Keep a snapshot of the request attributes in case of an include,
// to be able to restore the original attributes after the include.
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap<>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}
// Make framework objects available to handlers and view objects.
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
if (this.flashMapManager != null) {
FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
}
RequestPath requestPath = null;
if (this.parseRequestPath && !ServletRequestPathUtils.hasParsedRequestPath(request)) {
requestPath = ServletRequestPathUtils.parseAndCache(request);
}
try {
// 处理请求和响应
doDispatch(request, response);
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
if (requestPath != null) {
ServletRequestPathUtils.clearParsedRequestPath(request);
}
}
}
c>doDispatch()
所在类：org.springframework.web.servlet.DispatcherServlet
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
/*
mappedHandler：调用链
包含handler、interceptorList、interceptorIndex
handler：浏览器发送的请求所匹配的控制器方法
interceptorList：处理控制器方法的所有拦截器集合
interceptorIndex：拦截器索引，控制拦截器afterCompletion()的执行
*/
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
// 通过控制器方法创建相应的处理器适配器，调用所对应的控制器方法
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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
// 调用拦截器的preHandle()
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
// 由处理器适配器调用具体的控制器方法，最终获得ModelAndView对象
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
// 调用拦截器的postHandle()
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);
}
// 后续处理：处理模型数据和渲染视图
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);
}
}
}
}
d>processDispatchResult()
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
@Nullable Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
// 处理模型数据和渲染视图
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("No view rendering, null ModelAndView returned.");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
// Exception (if any) is already handled..
// 调用拦截器的afterCompletion()
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
4、SpringMVC的执行流程
-
用户向服务器发送请求，请求被SpringMVC 前端控制器 DispatcherServlet捕获。
-
DispatcherServlet对请求URL进行解析，得到请求资源标识符（URI），判断请求URI对应的映射：
a) 不存在
i. 再判断是否配置了mvc:default-servlet-handler
ii. 如果没配置，则控制台报映射查找不到，客户端展示404错误
iii. 如果有配置，则访问目标资源（一般为静态资源，如：JS,CSS,HTML），找不到客户端也会展示404错误
b) 存在则执行下面的流程
-
根据该URI，调用HandlerMapping获得该Handler配置的所有相关的对象（包括Handler对象以及Handler对象对应的拦截器），最后以HandlerExecutionChain执行链对象的形式返回。
-
DispatcherServlet 根据获得的Handler，选择一个合适的HandlerAdapter。
-
如果成功获得HandlerAdapter，此时将开始执行拦截器的preHandler(…)方法【正向】
-
提取Request中的模型数据，填充Handler入参，开始执行Handler（Controller)方法，处理请求。在填充Handler的入参过程中，根据你的配置，Spring将帮你做一些额外的工作：
a) HttpMessageConveter： 将请求消息（如Json、xml等数据）转换成一个对象，将对象转换为指定的响应信息
b) 数据转换：对请求消息进行数据转换。如String转换成Integer、Double等
c) 数据格式化：对请求消息进行数据格式化。 如将字符串转换成格式化数字或格式化日期等
d) 数据验证： 验证数据的有效性（长度、格式等），验证结果存储到BindingResult或Error中
-
Handler执行完成后，向DispatcherServlet 返回一个ModelAndView对象。
-
此时将开始执行拦截器的postHandle(…)方法【逆向】。
-
根据返回的ModelAndView（此时会判断是否存在异常：如果存在异常，则执行HandlerExceptionResolver进行异常处理）选择一个适合的ViewResolver进行视图解析，根据Model和View，来渲染视图。
-
渲染视图完毕执行拦截器的afterCompletion(…)方法【逆向】。
-
将渲染结果返回给客户端。
原文地址:https://blog.csdn.net/qq_39236499/article/details/134586909
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