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

9 Web开发——springmvc自动配置原理

 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

    9 Web开发——springmvc自动配置原理

9 Web开发——springmvc自动配置原理

9 Web开发——springmvc自动配置原理

  - 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 RequestMappingHandlerMappingRequestMappingHandlerAdapter, 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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