Spring整合SpringMVC

Spring整合SpringMVC的方式是父子容器形式
父容器Spring管理Service、Dao层的Bean
子容器SpringMVC管理Controller的Bean
子容器可以访问父容器的Bean,父容器无法访问子容器的Bean

而SpringBoot是SpringMVC零Xml配置基础上出现的，那SpringMVC的零Xml配置是如何实现的？

就是把web.xml中负责父容器ContextLoaderListener和子容器DispatcherServlet通过其他方式注入进来

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"><!--spring 基于web应用的启动--><listener><listener-class>org.springframework.web.context.c'c'c'c</listener-class></listener><!--全局参数：spring配置文件--><context-param><param-name>contextConfigLocation</param-name><param-value>classpath:spring-core.xml</param-value></context-param><!--配置前端控制器、核心调度器 加载spring容器--><servlet><servlet-name>springmvc</servlet-name><servlet-class>org.springframework.web.servlet.c'c</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:spring-mvc.xml</param-value></init-param><load-on-startup>1</load-on-startup><async-supported>true</async-supported></servlet><!--/ 除了jsp所有请求都会被匹配--><servlet-mapping><servlet-name>springmvc</servlet-name><url-pattern>/</url-pattern></servlet-mapping>
</web-app>

1. 零配置SpringMVC实现方式一：注解方式

@WebServlet
@WebFilter
@WebListener

这种方式不利于扩展，编写在jar包中tomcat无法感知到

2. 零配置SpringMVC实现方式一：SPI方式
   在Serlvet3-1的规范手册8.2.4：共享库可插拔方式
   https://javaee.github.io/servlet-spec/downloads/servlet-3.1/Final/servlet-3_1-final.pdf
   

自己应用：META-INF/services/javax.servlet.ServletContainerInitailizer ----- 即SPI规范

通过java.util.ServiceLoader.load(Interface.class) 可以完成SPI的实现类加载

SpringMVC中, 接口文件和实现类都把我们实现好了，ContextLoaderListener和DispatcherServlet都已注册，我们只让他生效即可

我们也可以自己提供动态添加servlet

/*** @HandlesTypes注解由Servlet容器提供支持（实现），* 参数中指定的所有实现类，利用字节码扫描框架（例如ASM、BCEL）从classpath中扫描出来，* 放入集合，传给回调方法onStartup的第一个参数** @HandlesTypes(WebApplicationInitializer.class)* Tomcat 启动时执行StandardContext的startInternal方法时，* 发布CONFIGURE_START_EVENT事件，ContextConfig会接收到此事件（ContextConfig.lifecycleEvent->configureStart->webConfig->processServletContainerInitializers加载ServletContainerInitializer实现类）* 并执行ServletContainerInitializer实现类的onStartup方法*/
@HandlesTypes(WebApplicationInitializer.class)
public class MxSpringServletContainerInitializer extends SpringServletContainerInitializer {/*** @param webAppInitializerClasses 感兴趣类的集合* {@link WebApplicationInitializer} found on the application classpath* @param servletContext Tomcat传过来的一个ServletContext* @throws ServletException*/@Overridepublic void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) throws ServletException {// 通过servletContext动态添加ServletservletContext.addServlet("mxSpiServlet", new HttpServlet() {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {resp.getWriter().write("mxSpiServlet--doGet");}}).addMapping("/mxSpiServlet.do");}
}

3. 基于SPI规范实现SpringMVC

WebApplicationInitializer的三个默认实现
AbstractContextLoaderInitializer
AbstractDispatcherServletInitializer
AbstractAnnotationConfigDispatcherServletInitializer

 * @author Chris Beams* @since 3.1* @see SpringServletContainerInitializer* @see org.springframework.web.context.AbstractContextLoaderInitializer* @see org.springframework.web.servlet.support.AbstractDispatcherServletInitializer* @see org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer*/
public interface WebApplicationInitializer {/*** Configure the given {@link ServletContext} with any servlets, filters, listeners* context-params and attributes necessary for initializing this web application. See* examples {@linkplain WebApplicationInitializer above}.* @param servletContext the {@code ServletContext} to initialize* @throws ServletException if any call against the given {@code ServletContext}* throws a {@code ServletException}*/void onStartup(ServletContext servletContext) throws ServletException;}

基于AbstractAnnotationConfigDispatcherServletInitializer的实现

/*** 通过spi的机制加载 classpath下ServletContainerInitializer* Tomcat 启动时执行StandardContext的startInternal方法时，* 发布CONFIGURE_START_EVENT事件，ContextConfig会接收到此事件（ContextConfig.lifecycleEvent->configureStart->webConfig->processServletContainerInitializers加载ServletContainerInitializer实现类）* 并执行ServletContainerInitializer实现类的onStartup方法*/
public class MxStarterInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {/*** 提供父容器的配置类* @return*/@Overrideprotected Class<?>[] getRootConfigClasses() {return new Class[]{RootConfig.class};}/*** 提供子容器的配置类* @return*/@Overrideprotected Class<?>[] getServletConfigClasses() {return new Class[]{WebAppConfig.class};}/*** 设置DispatcherServlet的映射* @return*/@Overrideprotected String[] getServletMappings() {return new String[]{"/"};}
}

父容器的配置类=以前的spring.xml
扫描的包排除@Controller
RootConfig.class

@Configuration
@ComponentScan(basePackages = "com.mx",excludeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION,value={Controller.class}),@ComponentScan.Filter(type = ASSIGNABLE_TYPE,value =WebAppConfig.class ),
})
public class RootConfig {
}

子容器的配置类=以前的spring-mvc.xml
扫描的包：包含@Controller
WebAppConfig.class

@Configuration
@ComponentScan(basePackages = {"com.mx"},includeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION,value = {RestController.class, Controller.class})
},useDefaultFilters =false)
@EnableWebMvc   // 替换之前的 <mvc:annotation-driven/>
public class WebAppConfig implements WebMvcConfigurer{/*** 配置拦截器* @return*/@Beanpublic TulingInterceptor tulingInterceptor() {return new TulingInterceptor();}/*** 文件上传下载的组件* @return*/@Beanpublic MultipartResolver multipartResolver() {CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver();multipartResolver.setDefaultEncoding("UTF-8");multipartResolver.setMaxUploadSize(1024*1024*10);return multipartResolver;}/*** 注册处理国际化资源的组件* @return*/@Beanpublic AcceptHeaderLocaleResolver localeResolver() {AcceptHeaderLocaleResolver acceptHeaderLocaleResolver = new AcceptHeaderLocaleResolver();return acceptHeaderLocaleResolver;}@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(tulingInterceptor()).addPathPatterns("/*");}/*** 配置视图解析器*/@Beanpublic InternalResourceViewResolver internalResourceViewResolver() {InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();viewResolver.setSuffix(".jsp");viewResolver.setPrefix("/WEB-INF/jsp/");return viewResolver;}/*不需要啊@Overridepublic void configureMessageConverters(List<HttpMessageConverter<?>> converters) {converters.add(new MappingJackson2HttpMessageConverter());}*/}

SPI的方式SpringMVC启动原理

Tomcat.startup->StandardContext->ContextConfig->ServletContainerInitializer->startup

1. 调用SpringServletContainerInitializer.onStartUp()

/** Copyright 2002-2020 the original author or authors.** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**      https://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/package org.springframework.web;import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ServiceLoader;
import java.util.Set;import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.HandlesTypes;import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.lang.Nullable;
import org.springframework.util.ReflectionUtils;/*** Servlet 3.0 {@link ServletContainerInitializer} designed to support code-based* configuration of the servlet container using Spring's {@link WebApplicationInitializer}* SPI as opposed to (or possibly in combination with) the traditional* {@code web.xml}-based approach.** <h2>Mechanism of Operation</h2>* This class will be loaded and instantiated and have its {@link #onStartup}* method invoked by any Servlet 3.0-compliant container during container startup assuming* that the {@code spring-web} module JAR is present on the classpath. This occurs through* the JAR Services API {@link ServiceLoader#load(Class)} method detecting the* {@code spring-web} module's {@code META-INF/services/javax.servlet.ServletContainerInitializer}* service provider configuration file. See the* <a href="https://download.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#Service%20Provider">* JAR Services API documentation</a> as well as section <em>8.2.4</em> of the Servlet 3.0* Final Draft specification for complete details.** <h3>In combination with {@code web.xml}</h3>* A web application can choose to limit the amount of classpath scanning the Servlet* container does at startup either through the {@code metadata-complete} attribute in* {@code web.xml}, which controls scanning for Servlet annotations or through an* {@code <absolute-ordering>} element also in {@code web.xml}, which controls which* web fragments (i.e. jars) are allowed to perform a {@code ServletContainerInitializer}* scan. When using this feature, the {@link SpringServletContainerInitializer}* can be enabled by adding "spring_web" to the list of named web fragments in* {@code web.xml} as follows:** <pre class="code">* &lt;absolute-ordering&gt;*   &lt;name>some_web_fragment&lt;/name&gt;*   &lt;name>spring_web&lt;/name&gt;* &lt;/absolute-ordering&gt;* </pre>** <h2>Relationship to Spring's {@code WebApplicationInitializer}</h2>* Spring's {@code WebApplicationInitializer} SPI consists of just one method:* {@link WebApplicationInitializer#onStartup(ServletContext)}. The signature is intentionally* quite similar to {@link ServletContainerInitializer#onStartup(Set, ServletContext)}:* simply put, {@code SpringServletContainerInitializer} is responsible for instantiating* and delegating the {@code ServletContext} to any user-defined* {@code WebApplicationInitializer} implementations. It is then the responsibility of* each {@code WebApplicationInitializer} to do the actual work of initializing the* {@code ServletContext}. The exact process of delegation is described in detail in the* {@link #onStartup onStartup} documentation below.** <h2>General Notes</h2>* In general, this class should be viewed as <em>supporting infrastructure</em> for* the more important and user-facing {@code WebApplicationInitializer} SPI. Taking* advantage of this container initializer is also completely <em>optional</em>: while* it is true that this initializer will be loaded and invoked under all Servlet 3.0+* runtimes, it remains the user's choice whether to make any* {@code WebApplicationInitializer} implementations available on the classpath. If no* {@code WebApplicationInitializer} types are detected, this container initializer will* have no effect.** <p>Note that use of this container initializer and of {@code WebApplicationInitializer}* is not in any way "tied" to Spring MVC other than the fact that the types are shipped* in the {@code spring-web} module JAR. Rather, they can be considered general-purpose* in their ability to facilitate convenient code-based configuration of the* {@code ServletContext}. In other words, any servlet, listener, or filter may be* registered within a {@code WebApplicationInitializer}, not just Spring MVC-specific* components.** <p>This class is neither designed for extension nor intended to be extended.* It should be considered an internal type, with {@code WebApplicationInitializer}* being the public-facing SPI.** <h2>See Also</h2>* See {@link WebApplicationInitializer} Javadoc for examples and detailed usage* recommendations.<p>** @author Chris Beams* @author Juergen Hoeller* @author Rossen Stoyanchev* @since 3.1* @see #onStartup(Set, ServletContext)* @see WebApplicationInitializer*/
@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {/*** Delegate the {@code ServletContext} to any {@link WebApplicationInitializer}* implementations present on the application classpath.* <p>Because this class declares @{@code HandlesTypes(WebApplicationInitializer.class)},* Servlet 3.0+ containers will automatically scan the classpath for implementations* of Spring's {@code WebApplicationInitializer} interface and provide the set of all* such types to the {@code webAppInitializerClasses} parameter of this method.* <p>If no {@code WebApplicationInitializer} implementations are found on the classpath,* this method is effectively a no-op. An INFO-level log message will be issued notifying* the user that the {@code ServletContainerInitializer} has indeed been invoked but that* no {@code WebApplicationInitializer} implementations were found.* <p>Assuming that one or more {@code WebApplicationInitializer} types are detected,* they will be instantiated (and <em>sorted</em> if the @{@link* org.springframework.core.annotation.Order @Order} annotation is present or* the {@link org.springframework.core.Ordered Ordered} interface has been* implemented). Then the {@link WebApplicationInitializer#onStartup(ServletContext)}* method will be invoked on each instance, delegating the {@code ServletContext} such* that each instance may register and configure servlets such as Spring's* {@code DispatcherServlet}, listeners such as Spring's {@code ContextLoaderListener},* or any other Servlet API componentry such as filters.* @param webAppInitializerClasses all implementations of* {@link WebApplicationInitializer} found on the application classpath* @param servletContext the servlet context to be initialized* @see WebApplicationInitializer#onStartup(ServletContext)* @see AnnotationAwareOrderComparator*/@Overridepublic void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)throws ServletException {List<WebApplicationInitializer> initializers = Collections.emptyList();if (webAppInitializerClasses != null) {initializers = new ArrayList<>(webAppInitializerClasses.size());for (Class<?> waiClass : webAppInitializerClasses) {// 接口和抽象类servlet容器也会给我们，但是我们不要// 排除接口和容器if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&WebApplicationInitializer.class.isAssignableFrom(waiClass)) {try {// 实例化，然后添加到集合中initializers.add((WebApplicationInitializer)ReflectionUtils.accessibleConstructor(waiClass).newInstance());}catch (Throwable ex) {throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);}}}}if (initializers.isEmpty()) {servletContext.log("No Spring WebApplicationInitializer types detected on classpath");return;}servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");AnnotationAwareOrderComparator.sort(initializers);// 调用initializer.onStartup  进行扩展for (WebApplicationInitializer initializer : initializers) {initializer.onStartup(servletContext);}}}

2. AbstractDispatcherServletInitializer.onStartup

	@Overridepublic void onStartup(ServletContext servletContext) throws ServletException {//实例化我们的spring上下文super.onStartup(servletContext);//注册我们的DispatcherServlet创建我们springweb上下文对象registerDispatcherServlet(servletContext);}

2.1 父容器
AbstractContextLoaderInitializer.onStartup

	@Overridepublic void onStartup(ServletContext servletContext) throws ServletException {registerContextLoaderListener(servletContext);}protected void registerContextLoaderListener(ServletContext servletContext) {// 创建父容器 ，WebApplicationContext rootAppContext = createRootApplicationContext();if (rootAppContext != null) {ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);// 设置初始化器listener.setContextInitializers(getRootApplicationContextInitializers());servletContext.addListener(listener);}else {logger.debug("No ContextLoaderListener registered, as " +"createRootApplicationContext() did not return an application context");}}

AbstractAnnotationConfigDispatcherServletInitializer.createRootApplicationContext
创建父容器，注册配置类

	@Override@Nullableprotected WebApplicationContext createRootApplicationContext() {Class<?>[] configClasses = getRootConfigClasses();if (!ObjectUtils.isEmpty(configClasses)) {AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();context.register(configClasses);return context;}else {return null;}}

2.2 子容器
AbstractDispatcherServletInitializer.registerDispatcherServlet

	protected void registerDispatcherServlet(ServletContext servletContext) {this.servletContext = servletContext;String servletName = getServletName();Assert.hasLength(servletName, "getServletName() must not return null or empty");// 创建子容器WebApplicationContext servletAppContext = createServletApplicationContext();Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");// 创建DispatcherServletFrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null");// 初始化器dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);if (registration == null) {throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +"Check if there is another servlet registered under the same name.");}// 启动时加载registration.setLoadOnStartup(1);// 映射registration.addMapping(getServletMappings());// 是否异步支持registration.setAsyncSupported(isAsyncSupported());// 设置DispatcherServlet的过滤器Filter[] filters = getServletFilters();if (!ObjectUtils.isEmpty(filters)) {for (Filter filter : filters) {registerServletFilter(servletContext, filter);}}// 空方法， 可以再对DispatcherServlet进行定制customizeRegistration(registration);}

AbstractAnnotationConfigDispatcherServletInitializer.createServletApplicationContext
创建子容器

	@Overrideprotected WebApplicationContext createServletApplicationContext() {AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();Class<?>[] configClasses = getServletConfigClasses();if (!ObjectUtils.isEmpty(configClasses)) {context.register(configClasses);}return context;}

3. 初始化ContextLoaderListener

Servlet的init方法 HttpServletBean.init->FrameworkServlet.initServletBean->FrameworkServlet.initWebApplicationContext

	protected WebApplicationContext initWebApplicationContext() {// 获得ContextLoaderListener存的父容器WebApplicationContext rootContext =WebApplicationContextUtils.getWebApplicationContext(getServletContext());WebApplicationContext wac = null;if (this.webApplicationContext != null) {// 获得子容器wac = this.webApplicationContext;if (wac instanceof ConfigurableWebApplicationContext) {ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;if (!cwac.isActive()) {// 如果没有设置父容器   spring  doGetBeanif (cwac.getParent() == null) {cwac.setParent(rootContext);}// 配置并且加载子容器configureAndRefreshWebApplicationContext(cwac);}}}if (wac == null) {// 从servlet上下文根据<contextAttribute>名字从域里面获取wac = findWebApplicationContext();}if (wac == null) {// xml会在这里创建wac = createWebApplicationContext(rootContext);}//refreshEventReceived 它会在容器加载完设置为true (通过事件onApplicationEvent)// springboot在这初始化组件if (!this.refreshEventReceived) {synchronized (this.onRefreshMonitor) {onRefresh(wac);}}if (this.publishContext) {// 将当前容器放到servlet域中， 可以再创建子容器String attrName = getServletContextAttributeName();getServletContext().setAttribute(attrName, wac);}return wac;}

FrameworkServlet.configureAndRefreshWebApplicationContext
配置并且加载子容器refrsh

	protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {if (ObjectUtils.identityToString(wac).equals(wac.getId())) {// 设置idif (this.contextId != null) {wac.setId(this.contextId);}else {// Generate default id...wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());}}// 设置servlet上下文wac.setServletContext(getServletContext());wac.setServletConfig(getServletConfig());wac.setNamespace(getNamespace());// 监听器  委托设计模式wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));// 将init-param设置到Environment中ConfigurableEnvironment env = wac.getEnvironment();if (env instanceof ConfigurableWebEnvironment) {((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());}// 空方法可扩展postProcessWebApplicationContext(wac);// 容器启动前初始化applyInitializers(wac);wac.refresh();}

AbstractApplicationContext.refresh (Spring核心方法)

4. 初始化DispatcherServlet

AbstractApplicationContext.refresh->AbstractApplicationContext.finishRefresh(Spring生命周期 lifecycleProcessor、发布事件 ContextRefreshedEvent)
publishEvent(new ContextRefreshedEvent(this))

FrameworkServlet 内部类ContextRefreshListener监听 ContextRefreshedEvent

	private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {@Overridepublic void onApplicationEvent(ContextRefreshedEvent event) {FrameworkServlet.this.onApplicationEvent(event);}}

FrameworkServlet.onApplicationEvent

	public void onApplicationEvent(ContextRefreshedEvent event) {this.refreshEventReceived = true;synchronized (this.onRefreshMonitor) {onRefresh(event.getApplicationContext());}}

FrameworkServlet实现类DispatcherServlet的onRefresh方法

	@Overrideprotected void onRefresh(ApplicationContext context) {initStrategies(context);}/**初始化策略,加了s都是多个* 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) {//初始化我们web上下文对象的 用于文件上传下载的解析器对象initMultipartResolver(context);//初始化我们web上下文对象用于处理国际化资源的initLocaleResolver(context);//主题解析器对象初始化initThemeResolver(context);//初始化我们的HandlerMappinginitHandlerMappings(context);//实例化我们的HandlerAdaptersinitHandlerAdapters(context);//实例化我们处理器异常解析器对象initHandlerExceptionResolvers(context);initRequestToViewNameTranslator(context);//给DispatcherSerlvet的ViewResolvers处理器initViewResolvers(context);initFlashMapManager(context);}

基本都是从容器中拿到已经配置的Bean（RequestMappingHandlerMapping、RequestMappingHandlerAdapter、HandlerExceptionResolver ）放到dispatcherServlet中做准备

这些类来自WebAppConfig中的@EnableWebMvc

EnableWebMvc

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(DelegatingWebMvcConfiguration.class)
public @interface EnableWebMvc {
}

DelegatingWebMvcConfiguration父类WebMvcConfigurationSupport就配置了这些Bean

	@Bean@SuppressWarnings("deprecation")public RequestMappingHandlerMapping requestMappingHandlerMapping(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,@Qualifier("mvcConversionService") FormattingConversionService conversionService,@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();...........

SpringBoot也是用的这种方式