SpringBoot-MVC自动配置原理

Spring MVC Auto-configuration

// Spring Boot为Spring MVC提供了自动配置，它可以很好地与大多数应用程序一起工作。

Spring Boot provides auto-configuration for Spring MVC that works well with most applications.

// 自动配置在Spring默认设置的基础上添加了以下功能：

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

// 包含视图解析器

Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.

// 支持静态资源文件夹的路径，以及webjars

Support for serving static resources, including support for WebJars

// 自动注册了Converter：

// 转换器，这就是我们网页提交数据到后台自动封装成为对象的东西，比如把"1"字符串自动转换为int类型

// Formatter：【格式化器，比如页面给我们了一个2019-8-10，它会给我们自动格式化为Date对象】

Automatic registration of Converter, GenericConverter, and Formatter beans.

// HttpMessageConverters

// SpringMVC用来转换Http请求和响应的的，比如我们要把一个User对象转换为JSON字符串，可以去看官网文档解释；

Support for HttpMessageConverters (covered later in this document).

// 定义错误代码生成规则的

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

// 首页定制

Static index.html support.

// 图标定制

Custom Favicon support (covered later in this document).

// 初始化数据绑定器：帮我们把请求数据绑定到JavaBean中！

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

/*

如果您希望保留Spring Boot MVC功能，并且希望添加其他MVC配置（拦截器、格式化程序、视图控制器和其他功能），则可以添加自己

的@configuration类，类型为webmvcconfiguer，但不添加@EnableWebMvc。如果希望提供

RequestMappingHandlerMapping、RequestMappingHandlerAdapter或ExceptionHandlerExceptionResolver的自定义

实例，则可以声明WebMVCregistrationAdapter实例来提供此类组件。

*/

If you want to keep Spring Boot MVC features and you want to add additional MVC configuration

(interceptors, formatters, view controllers, and other features), you can add your own

@Configuration class of type WebMvcConfigurer but without @EnableWebMvc. If you wish to provide

custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or

ExceptionHandlerExceptionResolver, you can declare a WebMvcRegistrationsAdapter instance to provide such components.

// 如果您想完全控制Spring MVC，可以添加自己的@Configuration，并用@EnableWebMvc进行注释。

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with 

@Bean

@ConditionalOnBean(ViewResolver.class)

@ConditionalOnMissingBean(name = "viewResolver", value = ContentNegotiatingViewResolver.class)

public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {

    ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();

    resolver.setContentNegotiationManager(beanFactory.getBean(ContentNegotiationManager.class));

    // ContentNegotiatingViewResolver使用所有其他视图解析器来定位视图，因此它应该具有较高的优先级

    resolver.setOrder(Ordered.HIGHEST_PRECEDENCE);

    return resolver;

}

@Nullable // 注解说明：@Nullable 即参数可为null

public View resolveViewName(String viewName, Locale locale) throws Exception {

    RequestAttributes attrs = RequestContextHolder.getRequestAttributes();

    Assert.state(attrs instanceof ServletRequestAttributes, "No current ServletRequestAttributes");

    List<MediaType> requestedMediaTypes = this.getMediaTypes(((ServletRequestAttributes)attrs).getRequest());

    if (requestedMediaTypes != null) {

        // 获取候选的视图对象

        List<View> candidateViews = this.getCandidateViews(viewName, locale, requestedMediaTypes);

        // 选择一个最适合的视图对象，然后把这个对象返回

        View bestView = this.getBestView(candidateViews, requestedMediaTypes, attrs);

        if (bestView != null) {

            return bestView;

        }

    }

    // .....

}

Iterator var5 = this.viewResolvers.iterator();

protected void initServletContext(ServletContext servletContext) {

    // 这里它是从beanFactory工具中获取容器中的所有视图解析器

    // ViewRescolver.class 把所有的视图解析器来组合的

    Collection<ViewResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(this.obtainApplicationContext(), ViewResolver.class).values();

    ViewResolver viewResolver;

    if (this.viewResolvers == null) {

        this.viewResolvers = new ArrayList(matchingBeans.size());

    }

    // ...............

}

@Bean //放到bean中

public ViewResolver myViewResolver(){

    return new MyViewResolver();

}

//我们写一个静态内部类，视图解析器就需要实现ViewResolver接口

private static class MyViewResolver implements ViewResolver{

    @Override

    public View resolveViewName(String s, Locale locale) throws Exception {

        return null;

    }

}

If you want to keep Spring Boot MVC features and you want to add additional MVC configuration (interceptors, formatters, view controllers, and other features), you can 
add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, 
or ExceptionHandlerExceptionResolver, you can declare a WebMvcRegistrationsAdapter instance to provide such components.

@Configuration

public class MyMvcConfig implements WebMvcConfigurer {

    @Override

    public void addViewControllers(ViewControllerRegistry registry) {

        // 浏览器发送/test ， 就会跳转到test页面；

        registry.addViewController("/test").setViewName("test");

    }

}