SpringBoot(四)

Web 场景

1.web 开发简介

Spring Boot provides auto-configuration for Spring MVC that works well with most applications.(大多场景我们都无需自定义配置)

The auto-configuration adds the following features on top of Spring’s defaults:

  • Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.

    • 内容协商视图解析器和 BeanName 视图解析器

  • Support for serving static resources, including support for WebJars (covered later in this document)).

    • 静态资源（包括 webjars）

  • Automatic registration of Converter, GenericConverter, and Formatter beans.

    • 自动注册 Converter，GenericConverter，Formatter

  • Support for HttpMessageConverters (covered later in this document).

    • 支持 HttpMessageConverters （后来我们配合内容协商理解原理）

  • Automatic registration of MessageCodesResolver (covered later in this document).

    • 自动注册 MessageCodesResolver （国际化用）

  • Static index.html support.

    • 静态 index.html 页支持

  • Custom Favicon support (covered later in this document).

    • 自定义 Favicon

  • Automatic use of a ConfigurableWebBindingInitializer bean (covered later in this document).

    • 自动使用 ConfigurableWebBindingInitializer ，（DataBinder 负责将请求数据绑定到 JavaBean 上）

If you want to keep those Spring Boot MVC customizations and make more MVC customizations (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc.

不用@EnableWebMvc 注解。使用 @Configuration + WebMvcConfigurer 自定义规则

If you want to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, and still keep the Spring Boot MVC customizations, you can declare a bean of type WebMvcRegistrations and use it to provide custom instances of those components.

声明 WebMvcRegistrations 改变默认底层组件

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc, or alternatively add your own @Configuration-annotated DelegatingWebMvcConfiguration as described in the Javadoc of @EnableWebMvc.

使用 @EnableWebMvc+@Configuration+DelegatingWebMvcConfiguration 全面接管SpringMVC

2.静态资源规则与定制化

静态资源目录

只要静态资源放在类路径下： called /static (or /public or /resources or /META-INF/resources
访问 ： 当前项目根路径/ + 静态资源名
原理： 静态映射/**。

请求进来，先去找 Controller 看能不能处理。不能处理的所有请求又都交给静态资源处理器。静态资源也找不到则响应 404 页面。

也可以改变默认的静态资源路径，/static，/public,/resources, /META-INF/resources失效

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spring:
  web:
    resources:
      static-locations: [classpath:/haha/]

静态资源访问前缀:

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spring:
  mvc:
    static-path-pattern: /res/**

当前项目 + static-path-pattern + 静态资源名 = 静态资源文件夹下找

webjar

可用 jar 方式添加 css，js 等资源文件，

https://www.webjars.org/

例如，添加 jquery

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<dependency>
    <groupId>org.webjars</groupId>
    <artifactId>jquery</artifactId>
    <version>3.7.1</version>
</dependency>

访问地址：http://localhost:8080/webjars/jquery/3.5.1/jquery.js 后面地址要按照依赖里面的包路径。

3. welcome 与 favicon 功能

官方文档

欢迎页支持

静态资源路径下 index.html。

  • 可以配置静态资源路径
  • 但是不可以配置静态资源的访问前缀。否则导致 index.html 不能被默认访问
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spring:
  #  mvc:
  #    static-path-pattern: /res/**   这个会导致welcome page功能失效
  web:
    resources:
      static-locations: [classpath:/haha/]
  • controller 能处理/index。

自定义 Favicon

指网页标签上的小图标。

favicon.ico 放在静态资源目录下即可。

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spring:
#  mvc:
#    static-path-pattern: /res/**   这个会导致 Favicon 功能失效

4.【源码分析】-静态资源原理

  • SpringBoot 启动默认加载 xxxAutoConfiguration 类（自动配置类）
  • SpringMVC 功能的自动配置类WebMvcAutoConfiguration，生效
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@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
    ...
}

给容器中配置的内容：

  • 配置文件的相关属性的绑定：WebMvcProperties==spring.mvc、ResourceProperties==spring.resources
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@Configuration(proxyBeanMethods = false)
@Import(EnableWebMvcConfiguration.class)
@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
@Order(0)
public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {
    ...
}

配置类只有一个有参构造器

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//有参构造器所有参数的值都会从容器中确定
public WebMvcAutoConfigurationAdapter(WebProperties webProperties, WebMvcProperties mvcProperties,
		ListableBeanFactory beanFactory, ObjectProvider<HttpMessageConverters> messageConvertersProvider,
		ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider,
		ObjectProvider<DispatcherServletPath> dispatcherServletPath,
		ObjectProvider<ServletRegistrationBean<?>> servletRegistrations) {
	this.mvcProperties = mvcProperties;
	this.beanFactory = beanFactory;
	this.messageConvertersProvider = messageConvertersProvider;
	this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
	this.dispatcherServletPath = dispatcherServletPath;
	this.servletRegistrations = servletRegistrations;
	this.mvcProperties.checkConfiguration();
}
  • ResourceProperties resourceProperties；获取和 spring.resources 绑定的所有的值的对象
  • WebMvcProperties mvcProperties 获取和 spring.mvc 绑定的所有的值的对象
  • ListableBeanFactory beanFactory Spring 的 beanFactory
  • HttpMessageConverters 找到所有的 HttpMessageConverters
  • ResourceHandlerRegistrationCustomizer 找到 资源处理器的自定义器。
  • DispatcherServletPath
  • ServletRegistrationBean 给应用注册 Servlet、Filter….

资源处理的默认规则

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...
public class WebMvcAutoConfiguration {
    ...
	public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {
        ...
		@Override
		protected void addResourceHandlers(ResourceHandlerRegistry registry) {
			super.addResourceHandlers(registry);
			if (!this.resourceProperties.isAddMappings()) {
				logger.debug("Default resource handling disabled");
				return;
			}
			ServletContext servletContext = getServletContext();
			addResourceHandler(registry, "/webjars/**", "classpath:/META-INF/resources/webjars/");
			addResourceHandler(registry, this.mvcProperties.getStaticPathPattern(), (registration) -> {
				registration.addResourceLocations(this.resourceProperties.getStaticLocations());
				if (servletContext != null) {
					registration.addResourceLocations(new ServletContextResource(servletContext, SERVLET_LOCATION));
				}
			});
		}
        ...

    }
    ...
}

根据上述代码，我们可以通过配置禁止所有静态资源规则。

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spring:
  web:
    resources:
      add-mappings: false #禁用所有静态资源规则

静态资源规则：

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@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {

    private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
            "classpath:/resources/", "classpath:/static/", "classpath:/public/" };

    /**
     * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
     * /resources/, /static/, /public/].
     */
    private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;
    ...
}

欢迎页的处理规则

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...
public class WebMvcAutoConfiguration {
    ...
	public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {
        ...
		@Bean
		public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
				FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
			WelcomePageHandlerMapping welcomePageHandlerMapping = new WelcomePageHandlerMapping(
					new TemplateAvailabilityProviders(applicationContext), applicationContext, getWelcomePage(),
					this.mvcProperties.getStaticPathPattern());
			welcomePageHandlerMapping.setInterceptors(getInterceptors(mvcConversionService, mvcResourceUrlProvider));
			welcomePageHandlerMapping.setCorsConfigurations(getCorsConfigurations());
			return welcomePageHandlerMapping;
		}

WelcomePageHandlerMapping的构造方法如下：

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WelcomePageHandlerMapping(TemplateAvailabilityProviders templateAvailabilityProviders,
                          ApplicationContext applicationContext, Resource welcomePage, String staticPathPattern) {
    if (welcomePage != null && "/**".equals(staticPathPattern)) {
        //要用欢迎页功能，必须是/**
        logger.info("Adding welcome page: " + welcomePage);
        setRootViewName("forward:index.html");
    }
    else if (welcomeTemplateExists(templateAvailabilityProviders, applicationContext)) {
        //调用Controller /index
        logger.info("Adding welcome page template: index");
        setRootViewName("index");
    }
}

这构造方法内的代码也解释了web 场景-welcome 与 favicon 功能中配置static-path-pattern了，welcome 页面和小图标失效的问题。