Spring Web MVC

M : Model

V : View

C : Controller -> DispatcherServlet

Front Controller = DispatcherServlet

Application Controller = @Controller or xx implements Controller

  • Context
    • ServletContextListener -> ContextLoaderListener -> Root WebApplicationContext
    • DispatcherServlet -> Servlet WebApplicationContext
  • Services
    • @Services
  • Repositories
    • @Repositories

映射处理

  • Servlet匹配规则
    • 精确匹配
      • /IndexServlet
    • 模糊匹配
      • /*.jsp
      • 当前目录下的所有目录
    • /匹配
      • /
      • 当前目录
  • Servlet请求映射
    • Servlet URL Pattern
    • Filter URL Pattern
  • Spring Web MVC
    • DispatcherServlet
    • HandlerMapping

@RestController=@Controller+@ResponseBody

org.springframework.web.bind.annotation.RestController

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package org.springframework.web.bind.annotation;
//ignore
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
//关键点
@Controller
@ResponseBody
public @interface RestController {

	/**
	 * The value may indicate a suggestion for a logical component name,
	 * to be turned into a Spring bean in case of an autodetected component.
	 * @return the suggested component name, if any (or empty String otherwise)
	 * @since 4.0.1
	 */
	@AliasFor(annotation = Controller.class)
	String value() default "";

}

DispatcherServlet < FrameworkServlet < HttpServletBean < HttpServlet

  • 新建项目，依赖Web
  • 新建packet->controller -> 新建Controller -> RestDemoController
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package com.bai.springwebmvc.controller;


import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * Rest Demo Controller
 */
@RestController
public class RestDemoController {
    @GetMapping
    public String index(){
        return "Hello World";
    }
}

浏览器访问:localhost:8080,页面显示“Hello World”。

问题及回答

Q ： 为什么Controller没有映射地址却能启动起来

A ： 自动装配，详情参见下面源码：org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration。此处的ServletContext path =”” or “/“，此二者等价。

Request URL = ServletContext path + @RequestMapping(“”) 或者 @GetMapping()

当前例子中，Request URL = “”+“”=“” -> RestDemoController#index

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package org.springframework.boot.autoconfigure.web.servlet;

// ignore import

@AutoConfigureOrder(-2147483648)
@Configuration
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@ConditionalOnClass({DispatcherServlet.class})
@AutoConfigureAfter({ServletWebServerFactoryAutoConfiguration.class})
@EnableConfigurationProperties({ServerProperties.class})
public class DispatcherServletAutoConfiguration {
  
	/*
	 * The bean name for a DispatcherServlet that will be mapped to the root URL "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";

	/*
	 * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

	@Configuration
	@Conditional(DefaultDispatcherServletCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
    //关键点
	@EnableConfigurationProperties(WebMvcProperties.class)
	protected static class DispatcherServletConfiguration {
      //ignore
    }
}

Q : 为什么访问localhost:8080可以调用到RestDemoController#index？

A : Spring MVC的处理方式是HandlerMapping自动寻找Request URL，匹配的Handler，Handler是处理的方法，当前这是一种实例。Request -> Handler -> 执行结果 -> 返回(Rest) -> 普通的文本。

HandlerMapping -> RequestMappingHandlerMapping -> @RequestMapping + Handler Mapping

补充

Spring Web MVC 的配置 Bean ：org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties

Spring Boot允许通过application.properties去定义配置，配置外部化。

WebMvcProperties配置前缀：spring.mvc

@PostMapping Post请求 @RequestMapping(method = RequestMethod.POST) Create(C)

@GetMapping Get请求 @RequestMapping(method = RequestMethod.GET) Read(R)

@PutMapping Put请求 @RequestMapping(method = RequestMethod.PUT) Update(R)

@DeleteMapping Delete请求 @RequestMapping(method = RequestMethod.DELETE) Delete(D)

无HeadMapping

拦截器：HandlerInterceptor ，可以理解handler到底是什么

如何装配

在启动类(xxxApplication,@SpringBootApplication) 继承WebMvcConfigurerAdapter(此类已经逐渐被淘汰)，重写addInterceptors方法，通过registry.addInterceptor方法将自定义拦截器装配。

处理顺序

preHandle(true) -> HandlerMethod(因为采用了@GetMapping，其它场景可能会有不同)执行(Method#invoke) -> postHandle -> afterCompletion

异常处理

  • Servlet标准
  • Spring Web MVC
  • Spring Boot

理解web.xml错误页面

传统的Servlet web.xml错误页面

Servlet -> web.xml(schema -> .xsd) -> 错误页面

处理逻辑：

  • 处理状态码
  • 处理异常类型
  • 处理服务
  • 优点
    • 统一处理，业界标准
  • 不足
    • 灵活度不够，只能定义在web.xml文件或annotation里面
Spring Web MVC 异常处理
  • @ExceptionHandler
  • @RestControllerAdvice=@ControllerAdvice+@ResponseBody
  • @ControllerAdvice专门拦截@Controller
Spring Boot错误处理页面
  • 实现ErrorPageRegistrar接口
  • 注册ErrorPage对象
  • 实现ErrorPage对象中的Path路径Web服务
  • 不足
    • 页面处理的路径必须笃定
  • 优点
    • 状态码
      • 比较通用，不需要理解SpringWebMVC异常体系
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package com.bai.springwebmvc;

import com.bai.springwebmvc.interceptor.DefaultHandlerInterceptor;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.server.ErrorPage;
import org.springframework.boot.web.server.ErrorPageRegistrar;
import org.springframework.boot.web.server.ErrorPageRegistry;
import org.springframework.http.HttpStatus;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@SpringBootApplication
public class SpringWebmvcApplication extends WebMvcConfigurerAdapter implements ErrorPageRegistrar{

	public static void main(String[] args) {
		SpringApplication.run(SpringWebmvcApplication.class, args);
	}

	@Override
	public void registerErrorPages(ErrorPageRegistry registry) {
		registry.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND,"/404.html"));
	}
}

视图技术

  • View
  • ViewResolver
    • ContentNegotiatingViewResolver
  • 实战
    • Thymeleaf

View

org.springframework.web.servlet.View#render

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void render(@Nullable Map<String, ?> model,
			HttpServletRequest request, HttpServletResponse response) throws Exception;
  • 处理页面渲染的逻辑
    • Velocity
    • JSP
    • Thymeleaf

ViewResolver

页面+解析器(resolve)

org.springframework.web.servlet.ViewResolver#resolveViewName

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/**
 * viewName : view的名称
 * locale   : 多语言(国际化)
 * 寻找对应的View对象
 * requestURI -> RequestMappingHandlerMaping -> HanleMethod ->
 * return "viewName" -> ViewResolver -> View -> render -> HTML
 * 完整的页面名称 = prefix + "viewName" + suffix
 */
@Nullable
	View resolveViewName(String viewName, Locale locale) throws Exception;

prefix 和 suffix 在org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties.View的属性内

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public static class View {
  /**
   * Spring MVC view prefix.
   */
  private String prefix;

  /**
   * Spring MVC view suffix.
   */
  private String suffix;
  //ignore
}
Spring Boot接续完整的页面路径

spring.view.prefix + hanlerMethod return + spring.view.suffix

自动装配类：org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration

进行自动装配，html不需要在web.xml里配置

配置项类：org.springframework.boot.autoconfigure.thymeleaf.ThymeleafProperties

配置项前缀：spring.thymeleaf

模板寻找前缀：spring.thymeleaf.prefix

模板寻找后缀：spring.thymeleaf.suffix

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package org.springframework.boot.autoconfigure.thymeleaf;
@ConfigurationProperties(prefix = "spring.thymeleaf")
public class ThymeleafProperties {

	private static final Charset DEFAULT_ENCODING = Charset.forName("UTF-8");

	public static final String DEFAULT_PREFIX = "classpath:/templates/";

	public static final String DEFAULT_SUFFIX = ".html";
  //ignore
}

ContentNegotiatingViewResolver

org.springframework.web.servlet.view.ContentNegotiatingViewResolver

  • 用于处理多个ViewResolver
    • JSP
    • Velocity
    • Thymeleaf
  • 当所有的ViewResover配置完成时，它们的order默认值时一样的，所以先来先服务(List)
  • 当它们定义自己的order，通过order来倒序排列
    • ViewResolver有优先级,排序在#getCandidateViews内
  • 流程
    • 得到CandidateViews(List)
    • 得到最匹配的View
    • render

代码示例

  • 添加maven依赖
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<!--Thymeleaf-->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
  • 修改默认配置
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<!--resources/application.properties-->
spring.thymeleaf.prefix = classpath:/thymeleaf/
spring.thymeleaf.suffix = .htm
  • 添加页面
    • resources下添加directory:thymeleaf
    • 在thymeleaf下添加file：index.htm
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<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>首页</title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
<!--/*@thymesVar id="name" type="java.lang.String"*/-->
<p th:text="#{home.welcome}"></p>
</body>
</html>
  • 添加controller
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package com.bai.springwebmvc.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@Controller
public class indexController {

    @RequestMapping
    public String index(){
        return "index";
    }
}
  • 浏览器访问localhost:8080，页面显示??home.welcome_zh_CN??

国际化(i18N)

  • Locale/LocaleContext
  • LocaleContextHolder
    • Spring内的对象
    • 缓存context
  • LocaleResolver/LocaleContextResolver

org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

代码示例

  • 修改application.properties
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spring.messages.basename=META-INF/locale/messages
  • 在上面的文件夹下添加文件
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#文件路径META-INF/locale/messages/messages.properties
home.welcome = welcome
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#文件路径META-INF/locale/messages/messages_zh_cn.properties
home.welcome = 欢迎
  • 访问localhost:8080,页面会根据浏览器的设置返回对应语言的文字

问题及回答

Q：遇到新问题如何查文档

A：在能定位错误范围的前提下，尽量不Google，找规范文档。解决问题后，读相关资料，不要为了解决问题而解决，而是要尽量扩充知识面，积累知识。

Q：怎么处理异常比较优雅

A：采用ExceptionHandler，代码层面易于理解。

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package com.bai.springwebmvc.controller;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import org.springframework.web.servlet.NoHandlerFoundException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.HashMap;
import java.util.Map;

@RestControllerAdvice
public class RestControllerAdvicer {
	//多个Exception中间用","分隔
    @ExceptionHandler({NoHandlerFoundException.class,IllegalAccessException.class})
    public  Object pageNotFound(HttpStatus status,HttpServletRequest request, Throwable throwable){
        Map<String,Object> errors =new HashMap<>();
        errors.put("statusCode",request.getAttribute("javax.servlet.error.status_code"));
        errors.put("requestUri",request.getAttribute("javax.servlet.error.request_uri"));
        return errors;
    }

    @ExceptionHandler(NullPointerException.class)
    public  Object handleNPE( Throwable throwable){

        return throwable.getMessage();
    }

}