SpringBoot2学习笔记

源码地址

四、Web开发

4.1）SpringMVC自动配置概述

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**

4.2）简单功能分析

4.2.1）静态资源访问

4.2.1.1）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

示例：工程中新建相应的文件夹，目录如下图

 浏览器访问：

1. http://localhost:8080/metainf.jpg，图片如下：

1. http://localhost:8080/public.gif，图片如下：

 http://localhost:8080/resources.jpg，图片如下：

 http://localhost:8080/public.gifhttp://localhost:8080/static.png，图片如下：

原理： 静态映射/**，拦截所以请求；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

新建 HelloController.java，代码如下：

@RestController
public class HelloController {
​
    @RequestMapping(\"/metainf.jpg\")
    public String hello(){
        return \"aaaa\";
    }
}

浏览器访问：http://localhost:8080/metainf.jpg，图片如下：

 改变默认的静态资源路径

4.2.2）静态资源访问前缀

默认无前缀，application.yaml，代码如下：

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

浏览器访问：http://localhost:8080/resources.jpg，页面报错，访问：http://localhost:8080/res/resources.jpg，页面可以正常访问，如下图：

 4.2.2.1）改变默认的静态资源路径

修改配置文件application.yaml，代码如下：

spring:
  mvc:
    # 静态资源访问默认无前缀
    static-path-pattern: /res/**
  resources:
    # 改变默认的静态资源路径
    static-locations: [classpath:/abc/]

浏览器访问：http://localhost:8080/resources.jpg，页面报错，访问：http://localhost:8080/res/abc.jpg，页面可以正常访问，如下图：

 4.2.3）欢迎页支持

1. 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

清空配置文件application.yaml，不使用额外配置【配置访问前缀会导致welcome page功能失效】，在resource目录下新建首页index.html，代码如下：

    
    


SpringBoot，欢迎您

浏览器访问默认地址：http://localhost:8080/，页面如下图：

 4.2.4）自定义 Favicon

自定义网页图标，favicon.ico 放在静态资源目录下即可，放到static目录下，浏览器访问默认地址：http://localhost:8080/，页面如下图：【配置访问前缀会导致自定义 Favicon功能失效】

 4.2.5）静态资源配置原理

• SpringBoot启动默认加载 xxxAutoConfiguration 类（自动配置类）

• SpringMVC功能的自动配置类 WebMvcAutoConfiguration，通过它实现资源配置，源码如下：

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@ConditionalOnClass({Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class})
@ConditionalOnMissingBean({WebMvcConfigurationSupport.class})
@AutoConfigureOrder(-2147483638)
@AutoConfigureAfter({DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class, ValidationAutoConfiguration.class})
public class WebMvcAutoConfiguration {
    public static final String DEFAULT_PREFIX = \"\";
    public static final String DEFAULT_SUFFIX = \"\";
    private static final String[] SERVLET_LOCATIONS = new String[]{\"/\"};
​
    public WebMvcAutoConfiguration() {
    }
    ...
}

4.2.5.1）配置类只有一个有参构造器

给容器中配置内容：WebMvcAutoConfigurationAdapter方法，配置文件的相关属性和xxx进行了绑定。WebMvcProperties==spring.mvc、ResourceProperties==spring.resources，源码如下：

@ConfigurationProperties(
    prefix = \"spring.mvc\"
)
public class WebMvcProperties {
    private org.springframework.validation.DefaultMessageCodesResolver.Format messageCodesResolverFormat;
    ...
}
​
——————————————————————————————————————————————————————————————————
@ConfigurationProperties(
    prefix = \"spring.resources\",
    ignoreUnknownFields = false
)
public class ResourceProperties {
    private static final String[] CLASSPATH_RESOURCE_LOCATIONS = new String[]{\"classpath:/META-INF/resources/\", \"classpath:/resources/\", \"classpath:/static/\", \"classpath:/public/\"};
    private String[] staticLocations;
    private boolean addMappings;
    private final ResourceProperties.Chain chain;
    private final ResourceProperties.Cache cache;
        ...
}

有参构造器所有参数的值都会从容器中确定：

• 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

• ServletRegistrationBean ： 给应用注册Servlet、Filter....

WebMvcAutoConfigurationAdapter方法，源码如下：

 @Configuration(
        proxyBeanMethods = false
    )
    @Import({WebMvcAutoConfiguration.EnableWebMvcConfiguration.class})
    @EnableConfigurationProperties({WebMvcProperties.class, ResourceProperties.class})
    @Order(0)
    public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {
        private static final Log logger = LogFactory.getLog(WebMvcConfigurer.class);
        private final ResourceProperties resourceProperties;
        private final WebMvcProperties mvcProperties;
        private final ListableBeanFactory beanFactory;
        private final ObjectProvider messageConvertersProvider;
        private final ObjectProvider dispatcherServletPath;
        private final ObjectProvider> servletRegistrations;
        final WebMvcAutoConfiguration.ResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer;
​
        public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties, WebMvcProperties mvcProperties, ListableBeanFactory beanFactory, ObjectProvider messageConvertersProvider, ObjectProvider resourceHandlerRegistrationCustomizerProvider, ObjectProvider dispatcherServletPath, ObjectProvider> servletRegistrations) {
            this.resourceProperties = resourceProperties;
            this.mvcProperties = mvcProperties;
            this.beanFactory = beanFactory;
            this.messageConvertersProvider = messageConvertersProvider;
            this.resourceHandlerRegistrationCustomizer = (WebMvcAutoConfiguration.ResourceHandlerRegistrationCustomizer)resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
            this.dispatcherServletPath = dispatcherServletPath;
            this.servletRegistrations = servletRegistrations;
        }
    ...
}

在配置文件application.yaml中可以设置禁用静态资源，代码如下：

spring:
  mvc:
    static-path-pattern: /res/**
​
  resources:
    # 禁用所有静态资源规则
    add-mappings: false 

4.2.5.2）欢迎页的处理规则

HandlerMapping：处理器映射。保存了每一个Handler能处理哪些请求。

WelcomePageHandlerMapping，源码如下

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