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24khandsome's Blog

SpringBoot02-webmvc

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SpringBoot-web相关开发

SpringBoot的web开发

webJar

​ 以jar包的形式来引入前端资源,比如jquery 或者是BootStrap：https://www.webjars.org

前端资源映射规则 核心源代码:WebMvcAutoConfiguration.WebMvcAutoConfigurationAdapter

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public void addResourceHandlers(ResourceHandlerRegistry registry) {
          if (!this.resourceProperties.isAddMappings()) {
              logger.debug("Default resource handling disabled");
          } else {
              this.addResourceHandler(registry, "/webjars/**", "classpath:/META-INF/resources/webjars/");
              this.addResourceHandler(registry, this.mvcProperties.getStaticPathPattern(), (registration) -> {
                  registration.addResourceLocations(this.resourceProperties.getStaticLocations());
                  if (this.servletContext != null) {
                      ServletContextResource resource = new ServletContextResource(this.servletContext, "/");
                      registration.addResourceLocations(new Resource[]{resource});
                  }

              });
          }
      }

访问：http://localhost:8080//webjars/jquery/3.3.1-2/jquery.js

控制台打印：

image-20210811233641951

源码追踪：

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org.springframework.web.servlet.resource.ResourceHttpRequestHandler#handleRequest方法 >org.springframework.web.servlet.resource.ResourceHttpRequestHandler#getResource >org.springframework.web.servlet.resource.ResourceResolverChain#resolveResource >org.springframework.web.servlet.resource.PathResourceResolver#resolveResourceInternal >org.springframework.web.servlet.resource.PathResourceResolver#getResource(真正的资源映射 处理逻辑)
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@Nullable
	private Resource getResource(String resourcePath, @Nullable HttpServletRequest request,
			List<? extends Resource> locations) {

		for (Resource location : locations) {
			try {
				String pathToUse = encodeOrDecodeIfNecessary(resourcePath, request, location);
				Resource resource = getResource(pathToUse, location);
				if (resource != null) {
					return resource;
				}
			}
			catch (IOException ex) {
				if (logger.isDebugEnabled()) {
					String error = "Skip location [" + location + "] due to error";
					if (logger.isTraceEnabled()) {
						logger.trace(error, ex);
					}
					else {
						logger.debug(error + ": " + ex.getMessage());
					}
				}
			}
		}
		return null;
	}

静态页面映射

我们直接把静态页面放在static的目录下，直接可以在路径直接访问

image-20210814182837595

Springboot整合springmvc

自动装配的组件

①:ContentNegotiatingViewResolver 和 BeanNameViewResolver 视图解析器 视图解析器的作用:根据方法的值找到对应的视图

②:Support for serving static resources, including support for WebJars 支持静态资源和webJars

③:Converter ,日期格式化器 Formatter

④:消息装换器: HttpMessageConverters

⑤:首页设置index.html

⑥:图标支持 Favicon

拓展SpringBoot的mvc配置

​ 自己写一个配置类 继承 WebMvcConfigurer 需要什么组件 就注册什么组件

如何往容器中添加一个拦截器

往容器中增加一个过滤器

往容器中增加一个servlet 

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@Configuration
public class MvcConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        HandlerInterceptor handlerInterceptor = new HandlerInterceptor() {
            @Override
            public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
                System.out.println("myHandlerInterceptor...前置拦截器:...");
                return true;
            }
        };
        registry.addInterceptor(handlerInterceptor).addPathPatterns("/**").excludePathPatterns("/index.html");
    }


    @Bean
    public FilterRegistrationBean filterRegistrationBean(){
        Filter filter = new Filter() {
            @Override
            public void init(FilterConfig filterConfig) throws ServletException {

            }

            @Override
            public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
                System.out.println("myFilter 的 doFilter方法");
                filterChain.doFilter(servletRequest,servletResponse);
            }

            @Override
            public void destroy() {

            }
        };

        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setFilter(filter);
        filterRegistrationBean.addUrlPatterns("/*"); return filterRegistrationBean;
    }

    @Bean
    public ServletRegistrationBean myHttpServlet(){

        HttpServlet httpServlet =  new HttpServlet() {

            @Override
            protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
                System.out.println("myHttpServlet");
                super.doPost(req,resp);
            }
        };
        ServletRegistrationBean  servletRegistration = new ServletRegistrationBean(httpServlet);
        servletRegistration.addUrlMappings("/hello1");

        return servletRegistration;
    }
}

接管springboot的mvc配置

方式：

​ 使用一个@EnableWebMvc来标识到配置类上,就会导致配置失效

原理：

​ @EnableWebMvc 为容器中导入了DelegatingWebMvcConfiguration的组件,是WebMvcConfigurationSupport的实现类，而WebMvcAutoConfiguration在WebMvcConfigurationSupport不存在时才会自动配置

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@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(DelegatingWebMvcConfiguration.class)
public @interface EnableWebMvc {
}

public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport

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@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration

SpringBoot错误处理机制

postman 请求 http://localhost:8080/hello3

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{
    "timestamp": 1629035261980,
    "status": 404,
    "error": "Not Found",
    "path": "/hello3"
}

浏览器

image-20210815215334258

如何跳转到/error

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DispatchServlet.doDispatch 找不到 返回
StandardHostValve.custom
ApplicationDispatcher.doForward 转发 到 /error

自动配置的异常处理的一些bean

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DefaultErrorAttributes
 	@Bean
	@ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
	public DefaultErrorAttributes errorAttributes() {
		return new DefaultErrorAttributes();
	}

BasicErrorController:/error请求处理控制器
	@Bean
	@ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)
	public BasicErrorController basicErrorController(ErrorAttributes errorAttributes,
			ObjectProvider<ErrorViewResolver> errorViewResolvers) {
		return new BasicErrorController(errorAttributes, this.serverProperties.getError(),
				errorViewResolvers.orderedStream().collect(Collectors.toList()));
	}

ErrorPageCustomizer:错误页面定制器
	@Bean
	public ErrorPageCustomizer errorPageCustomizer(DispatcherServletPath dispatcherServletPath) {
		return new ErrorPageCustomizer(this.serverProperties, dispatcherServletPath);
	}


DefaultErrorViewResolver
    @Bean
    @ConditionalOnBean(DispatcherServlet.class)
    @ConditionalOnMissingBean(ErrorViewResolver.class)
    DefaultErrorViewResolver conventionErrorViewResolver() {
        return new DefaultErrorViewResolver(this.applicationContext, this.resources);
    }
   
注入默认错误页面 defaultErrorView
	@Configuration(proxyBeanMethods = false)
	@ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true)
	@Conditional(ErrorTemplateMissingCondition.class)
	protected static class WhitelabelErrorViewConfiguration {

		private final StaticView defaultErrorView = new StaticView();

		@Bean(name = "error")
		@ConditionalOnMissingBean(name = "error")
		public View defaultErrorView() {
			return this.defaultErrorView;
		}

		// If the user adds @EnableWebMvc then the bean name view resolver from
		// WebMvcAutoConfiguration disappears, so add it back in to avoid disappointment.
		@Bean
		@ConditionalOnMissingBean
		public BeanNameViewResolver beanNameViewResolver() {
			BeanNameViewResolver resolver = new BeanNameViewResolver();
			resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
			return resolver;
		}

	}

处理/error请求的过程，以浏览器请求为例

  1. org.springframework.web.servlet.DispatcherServlet#doDispatch

    1. org.springframework.web.servlet.DispatcherServlet#getHandlerAdapter
      1. org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml （基础错误控制器）
        1. org.springframework.boot.autoconfigure.web.servlet.error.AbstractErrorController#resolveErrorView 遍历errorViewResolver 解析错误视图
          1. org.springframework.boot.autoconfigure.web.servlet.error.DefaultErrorViewResolver#resolveErrorView //查找error/“ + viewName视图是否存在，如果没有对应的解析精确匹配的状态码 使用模糊匹配比如4XX 5XX
        2. return (modelAndView != null) ? modelAndView : new ModelAndView(“error”, model);找不到对应解析器，则查找 error 对应的model
    2. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); 解析error视图View

定制错误异常信息

image-20210816095205231

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@ControllerAdvice
public class ExcepctionHandler {

    @ExceptionHandler(Exception.class)
    @ResponseBody
    public BasicResponse handlerException(Exception e){
        return BasicResponse.failed();
    }
}

@Data
public class BasicResponse<T>{

    private int code;
    private String msg;
    private T info;
    
    private static final Integer SUCCESS_CODE = 200;
    private static final String SUCCESS_MSG = "请求成功";
    private static final Integer FAIL_CODE = 500;
    private static final String FAIL_MSG = "服务器报错";

    public static BasicResponse success() {
        return new BasicResponse<>(SUCCESS_CODE,SUCCESS_MSG);
    }

    public static BasicResponse success(String successMsg) {
        return new BasicResponse<>(SUCCESS_CODE, successMsg);
    }

   

    public static BasicResponse failed() {
        return new BasicResponse<>(FAIL_CODE, FAIL_MSG);
    }

    public static BasicResponse failed(String failedMsg) {
        return new BasicResponse<>(FAIL_CODE, failedMsg);
    }

    public static <T> BasicResponse failed(String failedMsg,T object) {
        return new BasicResponse<>(FAIL_CODE, failedMsg,object);
    }

    public static BasicResponse failed(Integer code,String failedMsg) {
        return new BasicResponse<>(code, failedMsg);
    }


    private BasicResponse(int code, String msg) {
        this.code = code;
        this.msg = msg;
    }

    private BasicResponse(int code, String msg, T info) {
        this(code, msg);
        this.info = info;
    }
}