9 Web开发——springmvc自动配置原理

官方文档目录：

https://docs.spring.io/spring-boot/docs/2.1.0.RELEASE/reference/htmlsingle/#boot-features-spring-mvc

 1. Spring MVC auto-configuration

　　Spring Boot 自动配置好了SpringMVC,以下是SpringBoot对SpringMVC的默认配置:

（WebMvcAutoConfiguration）

　　- Inclusion of `ContentNegotiatingViewResolver` and `BeanNameViewResolver` beans.
　　- 自动配置了ViewResolver（视图解析器：根据方法的返回值得到视图对象（View），视图对象决定如何渲染（转发？重定向？））

    • public class WebMvcAutoConfiguration {
        @Bean
        @ConditionalOnMissingBean
        public InternalResourceViewResolver defaultViewResolver() {
            InternalResourceViewResolver resolver = new InternalResourceViewResolver();
            resolver.setPrefix(this.mvcProperties.getView().getPrefix());
            resolver.setSuffix(this.mvcProperties.getView().getSuffix());
            return resolver;
        }

        @Bean
        @ConditionalOnBean({View.class})
        @ConditionalOnMissingBean
        public BeanNameViewResolver beanNameViewResolver() {
            BeanNameViewResolver resolver = new BeanNameViewResolver();
            resolver.setOrder(2147483637);
            return resolver;
        }

        @Bean
        @ConditionalOnBean({ViewResolver.class})
        @ConditionalOnMissingBean(
            name = {"viewResolver"},
            value = {ContentNegotiatingViewResolver.class}
        )
        public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
            ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
            resolver.setContentNegotiationManager(
      　　(ContentNegotiationManager)beanFactory.getBean(ContentNegotiationManager.      class));
            resolver.setOrder(-2147483648);
            return resolver;
        }
    ......
}


　　　　- ContentNegotiatingViewResolver：只配置一个@RequestMapping， 匹配多个 url

  • public class ContentNegotiatingViewResolver implements ViewResolver, Ordered, InitializingBean { 
        @Nullable
    privateList<ViewResolver> viewResolvers;   //视图解析器

    //初始化方法
    protected void initServletContext(ServletContext servletContext) {
        //从容器中根据ViewResolver类型获取所有的视图解析器Collection<ViewResolver> matchingBeans = BeanFactoryUtils
                .beansOfTypeIncludingAncestors(this.obtainApplicationContext(), ViewResolver.class).values();
        ViewResolver viewResolver;
        if (this.viewResolvers == null) {
            this.viewResolvers = new ArrayList(matchingBeans.size());
            Iterator var3 = matchingBeans.iterator();

            //遍历所有的视图解析器
            while(var3.hasNext()) {
                viewResolver = (ViewResolver)var3.next();
                if (this != viewResolver) {
                    //将所有的视图解析器加入到本地变量
                    this.viewResolvers.add(viewResolver);
                }
            }
        } else {
            for(int i = 0; i < this.viewResolvers.size(); ++i) {
                viewResolver = (ViewResolver)this.viewResolvers.get(i);
                if (!matchingBeans.contains(viewResolver)) {
                    String name = viewResolver.getClass().getName() + i;
                    this.obtainApplicationContext().getAutowireCapableBeanFactory().initializeBean(viewResolver, name);
                }
            }
        }

        AnnotationAwareOrderComparator.sort(this.viewResolvers);
       this.cnmFactoryBean.setServletContext(servletContext);
    }


    @Nullable
    publicView 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) {//只配置一个@RequestMapping， 匹配多个 url，所以要获取多个
            List<View> candidateViews = this.getCandidateViews(viewName, locale, requestedMediaTypes);//获取所有候选的视图对象
            View bestView = this.getBestView(candidateViews, requestedMediaTypes, attrs);//获取最佳视图对象（根据参数或类型选取）
            if (bestView != null) {
                return bestView;
            }
        }

}
  • 自定义ViewResolver加入到Spring容器
  • //springBoot启动类注解，包含@Configuration
@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
    //将自定义的ViewResolver加入到Spring容器中
    @Bean
    public ViewResolver myViewResolver() {
        return new MyViewResover();
    }
    //自定义ViewResover
    public static class MyViewResover implements  ViewResolver {
        @Nullable
        @Override
        public View resolveViewName(String s, Locale locale) throws Exception {
            return null;
        }
    }
}
  •  当SpringBoot项目启动，随便发一个请求，进到DispatcherServlet的DoDispatch()方法时，能够获取到所有的ViewResolver,包括自定义的，被包含在了ContentNegotiatingViewResolver里

 　　　　


　　- 总结：如何定制视图解析器ViewResolver?：

　　　　根据@WebMvcAutoConfiguration

　　　　　　　　——》 @Bean ContentNegotiatingViewResolver viewResolver()

　　　　　　　　　　　　——》initServletContext（）中根据类型加载容器中所有的ViewResolver

　　　　我们可以自己给容器中添加一个视图解析器，@Bean加入到容器中，SpringBoot便自动的将其组合进来；

　　关于视图解析器详情在SprintMVC知识点中学习

 这些前面章节已有学过

　　- Support for serving static resources, including support for WebJars (see below).静态资源文件夹路径,webjars

　　- Static `index.html` support. 静态首页访问

　　- Custom `Favicon` support (see below). favicon.ico

- 自动注册了 of `Converter`, `GenericConverter`, `Formatter` beans.

　　- Converter：转换器； public String hello(User user)：类型转换使用Converter      （如果页面传参和User对象类型一一对应，不用转换，如果对应不上就需要转换）
　　- `Formatter` 格式化器； 2017.12.17   /   2017-12-17  / 2017/12/17===Date；　　（1：字符串转日期；2：按照给定的格式转）

    • 　　　　
@Configuration
@ConditionalOnWebApplication(
        type = ConditionalOnWebApplication.Type.SERVLET
)
@ConditionalOnClass({Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class})
@ConditionalOnMissingBean({WebMvcConfigurationSupport.class})
@AutoConfigureOrder(-2147483638)
@AutoConfigureAfter({DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class, ValidationAutoConfiguration.class})
public class WebMvcAutoConfiguration {

    @Configuration
    @Import({org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration.class})
    @EnableConfigurationProperties({WebMvcProperties.class, ResourceProperties.class})
    @Order(0)
    public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ResourceLoaderAware {
        private final ListableBeanFactory beanFactory;

        @Bean
        public FormattingConversionService mvcConversionService() {
            WebConversionService conversionService = new WebConversionService(this.mvcProperties.getDateFormat());
            this.addFormatters(conversionService);
            return conversionService;
        }

        protected void addFormatters(FormatterRegistry registry) {
            this.configurers.addFormatters(registry);
        }

        //添加格式化器
        public void addFormatters(FormatterRegistry registry) {
            //容器中符合Converter类型的bean都被格式化注册器FormatterRegistry注册进来
            Iterator var2 = this.getBeansOfType(Converter.class).iterator();

            while(var2.hasNext()) {
                Converter<?, ?> converter = (Converter)var2.next();
                registry.addConverter(converter);
            }

            //容器中符合GenericConverter类型的bean都被格式化注册器FormatterRegistry注册进来
            var2 = this.getBeansOfType(GenericConverter.class).iterator();

            while(var2.hasNext()) {
                GenericConverter converter = (GenericConverter)var2.next();
                registry.addConverter(converter);
            }

            //容器中符合Formatter类型的bean都被格式化注册器FormatterRegistry注册进来
            var2 = this.getBeansOfType(Formatter.class).iterator();

            while(var2.hasNext()) {
                Formatter<?> formatter = (Formatter)var2.next();
                registry.addFormatter(formatter);
            }

            /**
             *  从容器中获取所有从属于此类型的Bean
             *  自己添加的格式化器转换器，我们只需要放在容器中即可
          */
            private <T> Collection<T> getBeansOfType(Class<T> type) {
                return this.beanFactory.getBeansOfType(type).values();
            }
        }
    }
}

 

　　- HttpMessageConverter：SpringMVC用来转换Http请求和响应的；返回结果将　　User    ——》转化为　　Json；

　　- `HttpMessageConverters` 是从容器中确定；获取所有的HttpMessageConverter；

  •  　　　　　　　　　　
  • //@Configuration包含了@Component
@Configuration
public class WebMvcAutoConfiguration {
    public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ResourceLoaderAware {
        private final ObjectProvider<HttpMessageConverters> messageConvertersProvider;

        //通过构造方法从容器中注入进来
        public WebMvcAutoConfigurationAdapter(ObjectProvider<HttpMessageConverters> messageConvertersProvider,其它参数) {
            this.messageConvertersProvider = messageConvertersProvider;
        ......
        }
    }
}

//@Configuration包含了@Component
@Configuration
public class HttpMessageConverters implements Iterable<HttpMessageConverter<?>> {
    private final List<HttpMessageConverter<?>> converters;

    //
    public HttpMessageConverters(HttpMessageConverter... additionalConverters) {
        this((Collection) Arrays.asList(additionalConverters));
    }
    //通过构造方法从容器中注入进来
    public HttpMessageConverters(Collection<HttpMessageConverter<?>> additionalConverters) {
        this(true, additionalConverters);
    }
}

     自己给容器中添加HttpMessageConverter，只需要将自己的组件注册容器中（@Bean,@Component）

　　- Automatic registration of `MessageCodesResolver` (see below).定义错误代码生成规则

　　- Automatic use of a `ConfigurableWebBindingInitializer` bean (see below).

　　　　我们可以配置一个ConfigurableWebBindingInitializer来替换默认的；（添加到容器）

　　　　　　```初始化WebDataBinder；
　　　　　　```请求数据=====JavaBean；

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.

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

　总结：如何修改SpringBoot的默认配置？

​ 　　1）、SpringBoot在自动配置很多组件的时候，先看容器中有没有用户自己配置的（@Bean、@Component）如果有就用用户配置的，

　　　　如果没有，才自动配置；

　　　　如果有些组件可以有多个（ViewResolver）将用户配置的和自己默认的组合起来；

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原文地址：https://www.cnblogs.com/guchunchao/p/9898270.html