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Spring MVC 配置（10）

网友: 文章列表 2024-03-21 23:12:26

Spring MVC 配置（10）

目录

简介：

传统方式：

纯注解方式

1. Tomcat加载Servlet

 2.  参数分析

3. 调用onStartup方法

注解方法替换配置的 xml 文件

简介：

Spring MVC是Spring的一个子模块，也是我分析的Spring源码的最后一个模块。下面看一下Spring MVC的整个调用流程。

 看了上图，我们发现DispatcherServlet这个类是Spring MVC整个调用流程的核心。所有的请求和响应都是经过这个类进行处理的，那么分析这个类是势在必行的。

传统方式：

传统方式，我们都是在web.xml中配置2个重点的类，ContextLoaderListener和 DispatcherServlet

他们是Spring MVC的核心。

<!DOCTYPE web-app PUBLIC"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN""http://java.sun.com/dtd/web-app_2_3.dtd" ><web-app><context-param><param-name>contextConfigLocation</param-name><param-value><!--加载spring配置-->classpath:spring.xml</param-value></context-param><context-param><param-name>webAppRootKey</param-name><param-value>ServicePlatform.root</param-value></context-param><!-- 负责处理Spring相关的bean，类似于处理传统的spring.xml--><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class><!--<listener-class>org.springframework.web.context.request.RequestContextListener</listener-class>--></listener><!-- 负责处理Spring mvc 相关的bean，类似于处理传统的springmvc.xml, 此处我们定义的名称为spring-dispatcher.xml--><servlet><servlet-name>spring-dispatcher</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><!--springmvc的配置文件--><param-name>contextConfigLocation</param-name><param-value>classpath:spring-dispatcher.xml</param-value></init-param><!-- 这个参数大于等于0，代表它会随着容器的启动而加载 --><load-on-startup>0</load-on-startup></servlet><servlet-mapping><servlet-name>spring-dispatcher</servlet-name><url-pattern>/</url-pattern></servlet-mapping><!--静态文件处理--><!--<servlet-mapping><servlet-name>default</servlet-name><url-pattern>*.css</url-pattern></servlet-mapping><servlet-mapping><servlet-name>default</servlet-name><url-pattern>*.gif</url-pattern></servlet-mapping><servlet-mapping><servlet-name>default</servlet-name><url-pattern>*.jpg</url-pattern></servlet-mapping><servlet-mapping><servlet-name>default</servlet-name><url-pattern>*.js</url-pattern></servlet-mapping>-->
</web-app>

ContextLoaderListener： 负责加载Spring相关的操作，简单点说就是处理Spring.xml的

DispatcherServlet：处理Spring mvc相关操作，简单点说就是处理Spring MVC相关的xml文件的，并且还负责处理调用和响应，这个类是Spring MVC的核心。

纯注解方式

注解方式和传统方式需要实现一样的流程，因此，注解方式也要想办法通过注解实现传统方式中配置的 ContextLoaderListener 和 DispatcherServlet的功能。

无论是注解的方式，还是传统配置web.xml的方式，他们的核心主流程都是一样的。如下：

1. Tomcat加载Servlet

Tomcat启动的时候（web或severlet容器在初始化/启动的时候）  会加载/搜集 resources/META-INF路径下的com.xiangxue.jack.tomcat.ServletContainerInitializer文件，然后根据文件下配置的
信息去实例配置的类。

 2.  参数分析

Set<Class<?>> set ：存放的是实现了@HandlesTypes(WebApplicationInitializer.class)所有的类，就是实现了WebApplicationInitializer的类的class对象、

servletContext：Servlet的上下文类

/ Copyright 2002-2018 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      http://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.LinkedList;
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="http://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 = new LinkedList<>();if (webAppInitializerClasses != null) {for (Class<?> waiClass : webAppInitializerClasses) {// Be defensive: Some servlet containers provide us with invalid classes,// no matter what @HandlesTypes says...if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&WebApplicationInitializer.class.isAssignableFrom(waiClass)) {try {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);for (WebApplicationInitializer initializer : initializers) {initializer.onStartup(servletContext);}}}

3. 调用onStartup方法

在调用这个方法的时候，我们会进行 ContextLoaderListener 和 DispatcherServlet 的实例化操作

ContextLoaderListener ：实例化过程

 看一下具体是如何创建Spring上下文对象的, 其实它就是new了一个AnnotationConfigWebApplicationContext对象。

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

DispatcherServlet ：实例化

Spring MVC的上下文，也就是简单的new了一个 AnnotationConfigWebApplicationContext 对象

注解方法替换配置的 xml 文件

1. 首先需要定义2个扫描类，一个负责扫描到Spring文件，一个负责扫描SpringMVC的controller文件； 当然，也可以直接让Spring的扫描文件也把spring mvc 的 controller文件给扫描到，因为handlerMapping会有2个入口进行映射的处理，后面分析

2. 需要一个实现了 WebApplicationInitializer 的实现类，这样tomcat才能成功启动Spring MVC； 在这个实现类中，我们需要把扫描Spring和Spring MVC的2个类进行返回，这样ContextLoaderListener 和 DispatcherServlet 的钩子方法才能获取到要扫描的Spring文件 和 Spring MVC的文件路径，才能够正确的进行实例化Bean的操作。

3. 需要一个启动Spring MVC的的类，类似于启动AOP （@Aspect） 或 事务的注解类 （@EnableTransactionManagement(proxyTargetClass = false)）

Spring的扫描类：替换Spring.xml文件

package com.xiangxue.mvc.configuration;import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.FilterType;
import org.springframework.stereotype.Controller;//不扫描有@Controller注解的类
@ComponentScan(value = "com.xiangxue.jack",excludeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION,classes = {Controller.class})
})
public class SpringContainer {
}

Spring MVC的扫描类：扫描到controller对象

package com.xiangxue.mvc.configuration;import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.FilterType;
import org.springframework.stereotype.Controller;@ComponentScan(value = "com.xiangxue.mvc.controller",includeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION,classes = {Controller.class})
},useDefaultFilters = false)
public class MvcContainer {
}

WebApplicationInitializer的实现类：支持Spring MVC的启动，由tomcat负责

package com.xiangxue.mvc.mvc;import com.xiangxue.mvc.configuration.MvcContainer;
import com.xiangxue.mvc.configuration.SpringContainer;
import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;import javax.servlet.Filter;public class WebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {//父容器, 即spring扫描的注解类@Overrideprotected Class<?>[] getRootConfigClasses() {return new Class<?>[]{SpringContainer.class};}//spring mvc的扫描类@Overrideprotected Class<?>[] getServletConfigClasses() {return new Class<?>[]{MvcContainer.class};}//获取DispatcherServlet的映射信息@Overrideprotected String[] getServletMappings() {return new String[]{"/"};}@Overrideprotected Filter[] getServletFilters() {return super.getServletFilters();}
}

注解启动MVC的类：替换Spring-mvc.xml。里面的各种配置类都可以进行注入操作，比如拦截器UserInterceptor

package com.xiangxue.jack.mvc;import com.xiangxue.jack.interceptor.UserInterceptor;
import com.xiangxue.jack.interceptor.UserInterceptor1;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.config.annotation.*;
import org.springframework.web.servlet.view.json.MappingJackson2JsonView;import java.util.List;@Configuration
@EnableWebMvc
public class AppConfig extends WebMvcConfigurerAdapter {@Autowiredprivate UserInterceptor userInterceptor;@Overridepublic void configureViewResolvers(ViewResolverRegistry registry) {registry.enableContentNegotiation(new MappingJackson2JsonView());registry.jsp("/jsp/", ".jsp");}@Overridepublic void addViewControllers(ViewControllerRegistry registry) {registry.addViewController("/view/ok").setViewName("ok");registry.addViewController("/view/index").setViewName("index");}@Overridepublic void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {configurer.enable();}@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(userInterceptor).addPathPatterns("/user/").excludePathPatterns("/user/query/");registry.addInterceptor(new UserInterceptor1()).addPathPatterns("/user/").excludePathPatterns("");}@Overridepublic void addResourceHandlers(ResourceHandlerRegistry registry) {registry.addResourceHandler("/image/").addResourceLocations("classpath:/img/");}@Overridepublic void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {super.configureHandlerExceptionResolvers(exceptionResolvers);}/*    @Overridepublic void addCorsMappings(CorsRegistry registry) {registry.addMapping("/user/").allowedOrigins("*").allowCredentials(true).allowedMethods("GET", "POST", "DELETE", "PUT","PATCH").maxAge(3600);}*/
}

在SpringMVC.xml中，我们会定义各种各样的拦截器、转换器等等，我们都可以自己定义然后进行注入操作进行替换，下面我定义一个拦截器，并且在AppConfig类中进行注入：

拦截器类：

package com.xiangxue.jack.interceptor;import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;@Component
public class UserInterceptor implements HandlerInterceptor {//前置拦截方法@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("======UserInterceptor用户权限校验=========");return true;}//中置拦截方法@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("========UserInterceptor修改modelAndView======");}//后置拦截方法@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("========UserInterceptor资源释放======");}
}

至此，所有的配置类都已经完成。我们可以完全替换掉了Spring.xml 、SpringMVC.xml 和 web.xml文件了。

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