9 Web开发——springmvc自动配置原理-白红宇

9 Web开发——springmvc自动配置原理

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发布时间：2019-06-29

本文共 10340 字，大约阅读时间需要 34 分钟。

官方文档目录：

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;        }    ......}

　　　　- ：只配置一个@RequestMapping，匹配多个 url

public class ContentNegotiatingViewResolver implements ViewResolver, Ordered, InitializingBean {

@Nullable    privateList
       
         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
        
          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
         
           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
          
            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@SpringBootApplicationpublic 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 
     
       Collection
      
        getBeansOfType(Class
       
         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@Configurationpublic class WebMvcAutoConfiguration {    public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ResourceLoaderAware {        private final ObjectProvider
       
         messageConvertersProvider;        //通过构造方法从容器中注入进来        public WebMvcAutoConfigurationAdapter(ObjectProvider
        
          messageConvertersProvider,其它参数) {            this.messageConvertersProvider = messageConvertersProvider;        ......        }    }}//@Configuration包含了@Component@Configurationpublic class HttpMessageConverters implements Iterable
         
          > {    private final List
          
           > 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
           
            > 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 (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；

转载于:https://www.cnblogs.com/guchunchao/p/9898270.html

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