理解Spring Web MVC架構(gòu)

基礎(chǔ)架構(gòu)：Servlet

• 特點(diǎn)
  • 請(qǐng)求/響應(yīng)式（Request/Response）
  • 屏蔽網(wǎng)絡(luò)通訊細(xì)節(jié)
• API特性
  • 面向HTTP協(xié)議
  • 完整生命周期
• 職責(zé)
• 處理請(qǐng)求
• 資源管理（數(shù)據(jù)庫(kù)連接况毅、消息連接、其他）
• 視圖渲染

核心架構(gòu)：前端控制器（Front Controller）

• 資源 ： http://www.corej2eepatterns.com/FrontController.htm
• 實(shí)現(xiàn) ：Spring Web MVC DispatchServlet
  • https://docs.spring.io/spring/docs/1.0.0/javadoc-api/org/springframework/web/servlet/DispatcherServlet.html

Spring Web MVC 架構(gòu)

認(rèn)識(shí)Spring Web MVC

Spring Framework時(shí)代的一般認(rèn)識(shí)

實(shí)現(xiàn)Controller

@Controller
public class HelloWorldController {
    @RequestMapping("")
    public String index() {
        return "index";
    }
}

配置 Web MVC 組件

 
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
    <context:component-scan base-package="com.imooc.web"/>
    <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"/>
    <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"/>
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
</beans>

部署DispatchServlet

<web-app>
    <servlet>
    <servlet-name>app</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/app-context.xml</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>app</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

使用可執(zhí)行 Tomcat Maven 插件

 
<plugin>
    <groupId>org.apache.tomcat.maven</groupId>
    <artifactId>tomcat7-maven-plugin</artifactId>
    <version>2.1</version>
    <executions>
        <execution>
            <id>tomcat-run</id>
            <goals>
                <goal>exec-war-only</goal>
            </goals>
            <phase>package</phase>
            <configuration>
                <!-- ServletContext path -->
                <path>/</path>
            </configuration>
        </execution>
    </executions>
</plugin>

Spring Framework時(shí)代的重新認(rèn)識(shí)

Web MVC 核心組件

交互流程

MVC 注解驅(qū)動(dòng)

• 版本依賴

  • Spring Framework3.1+

• 基本配置步驟

  • 注解配置：@Configuration（Spring 范氏注解）
  • 組件激活：@EnableWebMvc （Spring模塊裝配）
  • 自定義組件：WebMvcConfigurer(Spring Bean)

• 重構(gòu)代碼：

@ComponentScan(basePackages = "com.imooc.web")
public class DispatchServletConfig {

}

@Configuration
@EnableWebMvc
public class WebMvcConfig implements WebMvcConfigurer {
    @Bean
    public ViewResolver viewResolver(){
        InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
        viewResolver.setViewClass(JstlView.class);
        viewResolver.setPrefix("/WEB-INF/jsp/");
        viewResolver.setSuffix(".jsp");
        return viewResolver;
    }
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new HandlerInterceptor() {
            @Override
            public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
                System.out.println("攔截中....");
                return true;
            }
        });
    }

}

• 常用注解
  • 注冊(cè)模型屬性：@ModelAttribute
  • 讀取請(qǐng)求頭：@RequestHeader
  • 讀取Cookie：@CookieValue
  • 校驗(yàn)參數(shù)：@Valid茉贡、@Validated

@Controller
public class HelloWorldController {
    @RequestMapping
    public String index(@RequestHeader("Accept-Language")String acceptLanguage,@CookieValue("JSESSIONID")String jsessionId, Model model){
//        model.addAttribute("acceptLanguage",acceptLanguage);
//        model.addAttribute("jsessionId",jsessionId);
//        model.addAttribute("message","hello,world");
        return "index";
    }
}

@ControllerAdvice(assignableTypes = HelloWorldController.class)
public class HelloWorldControllerAdvice {
    @ModelAttribute("acceptLanguage")
    public String acceptLanguage(@RequestHeader("Accept-Language")String acceptLanguage){
        return acceptLanguage;
    }

    @ModelAttribute("jsessionId")
    public String jsessionId(@CookieValue("JSESSIONID")String jsessionId){
        return jsessionId;
    }

    @ModelAttribute("message")
    public String message(){
        return "hello,world";
    }
    @ExceptionHandler(Throwable.class)
    public ResponseEntity<String> onException(Throwable throwable){
        return ResponseEntity.ok(throwable.getMessage());
    }
}

自動(dòng)裝配

• 版本依賴
  • Spring Framework3.1+
  • Servlet 3.0+

Servlet SPI

• ServletContainerInitializer,參考Servlet3.0 規(guī)范
• 配合 @HandlesTypes

Spring 適配

org.springframework.web.SpringServletContainerInitializer

Spring SPI

• 基礎(chǔ)接口：org.springframework.web.WebApplicationInitializer
• 編程驅(qū)動(dòng)：org.springframework.web.servlet.support.AbstractDispatcherServletInitializer
• 注解驅(qū)動(dòng)：org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer

public class DefaultAnnotationConfigDispatcherServletInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
    //web.xml
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[0];
    }
    //dispatchServlet
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[]{DispatchServletConfig.class};
    }

    @Override
    protected String[] getServletMappings() {
        return new String[]{"/"};
    }
}

Spring Boot 時(shí)代簡(jiǎn)化Spring Web MVC

完全自動(dòng)裝配

• 自動(dòng)裝配DispatcherServlet：org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration
  • 裝配條件:

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
@EnableConfigurationProperties(ServerProperties.class)

• 替換@EnableWebMvc：org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration
  • 裝配條件:

@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
        ValidationAutoConfiguration.class })

• Servlet 容器：org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration

理解自動(dòng)裝配順序性

• 絕對(duì)順序：@AutoConfigureOrder
• 相對(duì)順序：@AutoConfigureAfter

裝配條件

Web類型判斷（@ConditionalOnWebApplication）

• WebApplicationType
  • Servlet類型：WebApplicationType.SERVLET

API判斷（@ConditionalOnClass）

• Servlet
  • Servlet
• Spring Web MVC
  • org.springframework.web.servlet.DispatcherServlet
  • org.springframework.web.servlet.config.annotation.WebMvcConfigurer

Bean判斷（@ConditionalOnMissingBean、@ConditionalOnBean）

org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport

外部化配置

Web MVC配置

org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties

spring.mvc.view.prefix = /WEB-INF/jsp/
spring.mvc.view.suffix = .jsp

Spring Boot JSP依賴

 <!-- Provided -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <scope>provided</scope>
</dependency>
<dependency>
    <groupId>org.apache.tomcat.embed</groupId>
    <artifactId>tomcat-embed-jasper</artifactId>
    <scope>provided</scope>
</dependency>