05springboot web开发(3)

7、文件上传

1.单文件与多文件上传的使用

• 页面代码

  /static/form/form_layouts.html

  • 多文件上传, 使用multiple

<form role="form" th:action="@{/upload}" method="post" enctype="multipart/form-data">
    <div class="form-group">
        <label for="exampleInputEmail1">邮箱</label>
        <input type="email" name="email" class="form-control" id="exampleInputEmail1" placeholder="Enter email">
    </div>
    
    <div class="form-group">
        <label for="exampleInputPassword1">名字</label>
        <input type="text" name="username" class="form-control" id="exampleInputPassword1" placeholder="Password">
    </div>
    
    <div class="form-group">
        <label for="exampleInputFile">头像</label>
        <input type="file" name="headerImg" id="exampleInputFile">
    </div>
    
    <div class="form-group">
        <label for="exampleInputFile">生活照</label>
        <input type="file" name="photos" multiple>   <!--多文件上传, 使用multiple -->
    </div>
    
    <div class="checkbox">
        <label>
            <input type="checkbox"> Check me out
        </label>
    </div>
    <button type="submit" class="btn btn-primary">提交</button>
</form>

• 控制层代码

MultipartFile自动封装上传的文件

@Slf4j
@Controller
public class FormTestController {

    @GetMapping("/form_layouts")
    public String form_layouts(){
        return "form/form_layouts";
    }

    @PostMapping("/upload")
    public String upload(@RequestParam("email") String email,
                         @RequestParam("username") String username,
                         @RequestPart("headerImg") MultipartFile headerImg,
                         @RequestPart("photos") MultipartFile[] photos) throws IOException {

        log.info("上传的信息：email={}，username={}，headerImg={}，photos={}", 
                 email,username,headerImg.getSize(),photos.length);

        if(!headerImg.isEmpty()){
            //保存到文件服务器，OSS服务器
            String originalFilename = headerImg.getOriginalFilename(); 
            // 获取文件名 , getName() 是获取标签的名字(name="headerImg")
            headerImg.transferTo(new File("H:\\cache\\"+originalFilename));
        }

        if(photos.length > 0){
            for (MultipartFile photo : photos) {
                if(!photo.isEmpty()){
                    String originalFilename = photo.getOriginalFilename();
                    photo.transferTo(new File("H:\\cache\\"+originalFilename));
                }
            }
        }


        return "main";
    }
}

文件上传相关的配置类：

• org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration
• org.springframework.boot.autoconfigure.web.servlet.MultipartProperties

文件大小相关配置项：

spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=100MB

2.文件上传参数解析器[源码分析]

文件上传相关的自动配置类MultipartAutoConfiguration

• 自动配置好了StandardServletMultipartResolver [文件上传解析器]
• 如果有需求可以自己配置文件上传解析器

原理步骤:

1. 请求进来使用文件上传解析器判断（isMultipart）并封装（resolveMultipart，返回MultipartHttpServletRequest）文件上传请求
2. 参数解析器来解析请求中的文件内容封装成MultipartFile
3. 将request中文件信息封装为一个Map；MultiValueMap<String, MultipartFile>

FileCopyUtils。实现文件流的拷贝

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ Servlet.class, StandardServletMultipartResolver.class, MultipartConfigElement.class })
@ConditionalOnProperty(prefix = "spring.servlet.multipart", name = "enabled", matchIfMissing = true)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(MultipartProperties.class)
public class MultipartAutoConfiguration {

	private final MultipartProperties multipartProperties;

	public MultipartAutoConfiguration(MultipartProperties multipartProperties) {
		this.multipartProperties = multipartProperties;
	}

	@Bean
	@ConditionalOnMissingBean({ MultipartConfigElement.class, CommonsMultipartResolver.class })
	public MultipartConfigElement multipartConfigElement() {
		return this.multipartProperties.createMultipartConfig();
	}

	@Bean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
	@ConditionalOnMissingBean(MultipartResolver.class)
	public StandardServletMultipartResolver multipartResolver() {
        //配置好文件上传解析器
		StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
		multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
		return multipartResolver;
	}

}
//文件上传解析器
public class StandardServletMultipartResolver implements MultipartResolver {

	private boolean resolveLazily = false;

	public void setResolveLazily(boolean resolveLazily) {
		this.resolveLazily = resolveLazily;
	}


	@Override
	public boolean isMultipart(HttpServletRequest request) {
		return StringUtils.startsWithIgnoreCase(request.getContentType(), "multipart/");
	}

	@Override
	public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {
		return new StandardMultipartHttpServletRequest(request, this.resolveLazily);
	}

	@Override
	public void cleanupMultipart(MultipartHttpServletRequest request) {
		if (!(request instanceof AbstractMultipartHttpServletRequest) ||
				((AbstractMultipartHttpServletRequest) request).isResolved()) {
			// To be on the safe side: explicitly delete the parts,
			// but only actual file parts (for Resin compatibility)
			try {
				for (Part part : request.getParts()) {
					if (request.getFile(part.getName()) != null) {
						part.delete();
					}
				}
			}
			catch (Throwable ex) {
				LogFactory.getLog(getClass()).warn("Failed to perform cleanup of multipart items", ex);
			}
		}
	}

}
public class DispatcherServlet extends FrameworkServlet {
    
    @Nullable
	private MultipartResolver multipartResolver;
    
	private void initMultipartResolver(ApplicationContext context) {
		...
        
        //这个就是配置类配置的StandardServletMultipartResolver文件上传解析器
		this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
		...
	}
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;//最后finally的回收flag
		...
		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
                //做预处理,如果有上传文件 就new StandardMultipartHttpServletRequest包装类
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);
				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				
                ...

				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				...

				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                
            }
            ....
            
		finally {

            ...
            
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
		}
	}

	protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
		if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
            ...
			return this.multipartResolver.resolveMultipart(request);
            ...
		}
    }

	protected void cleanupMultipart(HttpServletRequest request) {
		if (this.multipartResolver != null) {
			MultipartHttpServletRequest multipartRequest =
					WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
			if (multipartRequest != null) {
				this.multipartResolver.cleanupMultipart(multipartRequest);
			}
		}
	}
}

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());跳到以下的类

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {
	@Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
		ModelAndView mav;
		...
		mav = invokeHandlerMethod(request, response, handlerMethod);
        ...
		return mav;
	}
    
    @Nullable
	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
			WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
			ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

			ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			if (this.argumentResolvers != null) {//关注点
				invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			}
			...
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			...

			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
			webRequest.requestCompleted();
		}
	}
    
}

this.argumentResolvers其中主角类RequestPartMethodArgumentResolver用来生成

public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
    
    ...
	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		...
	}
    
	@Nullable
	public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
		...
		return doInvoke(args);//反射调用
	}
    
	@Nullable
	protected Object doInvoke(Object... args) throws Exception {
		Method method = getBridgedMethod();
		ReflectionUtils.makeAccessible(method);
		return method.invoke(getBean(), args);
		...
	}
    
    //处理得出multipart参数，准备稍后的反射调用（@PostMapping标记的上传方法）
    protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		MethodParameter[] parameters = getMethodParameters();
		...
		Object[] args = new Object[parameters.length];
		for (int i = 0; i < parameters.length; i++) {
			MethodParameter parameter = parameters[i];
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = findProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
				continue;
			}
            //关注点1
			if (!this.resolvers.supportsParameter(parameter)) {
				throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
			}
			try {
                //关注点2
				args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
			}
			catch (Exception ex) {
				...
			}
		}
		return args;
	}
    
}
public class RequestPartMethodArgumentResolver extends AbstractMessageConverterMethodArgumentResolver {

    //对应上面代码关注点1
    @Override
	public boolean supportsParameter(MethodParameter parameter) {
        //标注@RequestPart的参数
		if (parameter.hasParameterAnnotation(RequestPart.class)) {
			return true;
		}
		else {
			if (parameter.hasParameterAnnotation(RequestParam.class)) {
				return false;
			}
			return MultipartResolutionDelegate.isMultipartArgument(parameter.nestedIfOptional());
		}
	}

    //对应上面代码关注点2
	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest request, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);
		Assert.state(servletRequest != null, "No HttpServletRequest");

		RequestPart requestPart = parameter.getParameterAnnotation(RequestPart.class);
		boolean isRequired = ((requestPart == null || requestPart.required()) && !parameter.isOptional());

		String name = getPartName(parameter, requestPart);
		parameter = parameter.nestedIfOptional();
		Object arg = null;

        //封装成MultipartFile类型的对象作参数
		Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);
		if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
			arg = mpArg;
		}
        
        ...

		return adaptArgumentIfNecessary(arg, parameter);
	}
}
public final class MultipartResolutionDelegate {
    ...
    
	@Nullable
	public static Object resolveMultipartArgument(String name, MethodParameter parameter, HttpServletRequest request)
			throws Exception {

		MultipartHttpServletRequest multipartRequest =
				WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
		boolean isMultipart = (multipartRequest != null || isMultipartContent(request));

		if (MultipartFile.class == parameter.getNestedParameterType()) {
			if (!isMultipart) {
				return null;
			}
			if (multipartRequest == null) {
				multipartRequest = new StandardMultipartHttpServletRequest(request);
			}
			return multipartRequest.getFile(name);
		}
		else if (isMultipartFileCollection(parameter)) {
			if (!isMultipart) {
				return null;
			}
			if (multipartRequest == null) {
				multipartRequest = new StandardMultipartHttpServletRequest(request);
			}
			List<MultipartFile> files = multipartRequest.getFiles(name);
			return (!files.isEmpty() ? files : null);
		}
		else if (isMultipartFileArray(parameter)) {
			if (!isMultipart) {
				return null;
			}
			if (multipartRequest == null) {
				multipartRequest = new StandardMultipartHttpServletRequest(request);
			}
			List<MultipartFile> files = multipartRequest.getFiles(name);
			return (!files.isEmpty() ? files.toArray(new MultipartFile[0]) : null);
		}
		else if (Part.class == parameter.getNestedParameterType()) {
			if (!isMultipart) {
				return null;
			}
			return request.getPart(name);
		}
		else if (isPartCollection(parameter)) {
			if (!isMultipart) {
				return null;
			}
			List<Part> parts = resolvePartList(request, name);
			return (!parts.isEmpty() ? parts : null);
		}
		else if (isPartArray(parameter)) {
			if (!isMultipart) {
				return null;
			}
			List<Part> parts = resolvePartList(request, name);
			return (!parts.isEmpty() ? parts.toArray(new Part[0]) : null);
		}
		else {
			return UNRESOLVABLE;
		}
	}
    
    ...
    
}

8、异常处理

1.错误处理-SpringBoot默认错误处理机制

Spring Boot官方文档 - Error Handling

默认规则：

• 默认情况下，Spring Boot提供/error处理所有错误的映射
• 对于机器客户端，它将生成JSON响应，其中包含错误，HTTP状态和异常消息的详细信息。
• 对于浏览器客户端，响应一个“ whitelabel”错误视图，以HTML格式呈现相同的数据

{
  "timestamp": "2020-11-22T05:53:28.416+00:00",
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/asadada"
}

• 要对其进行自定义，添加View解析为error
• 要完全替换默认行为，可以实现 ErrorController并注册该类型的Bean定义，或添加ErrorAttributes类型的组件以使用现有机制但替换其内容。
• /templates/error/下的4xx，5xx页面会被自动解析

自定义错误页面的做法

也可以获取错误信息:

• JSON中有的都可以获取

<h3 th:text="${message}">Something went wrong.</h3>
<p class="nrml-txt" th:text="${trace}">Why not try refreshing you page? Or you can <a href="#">contact our support</a> if the problem persists.</p>
<a class="back-btn" href="index.html" th:text="${status}"> Back To Home</a>

2.异常处理自动配置原理

• ErrorMvcAutoConfiguration 自动配置异常处理规则

• 容器中的组件：类型：DefaultErrorAttributes -> id：errorAttributes

• public class DefaultErrorAttributes implements ErrorAttributes, HandlerExceptionResolver

  • DefaultErrorAttributes：定义错误页面中可以包含数据（异常明细，堆栈信息等）。

• 容器中的组件：类型：BasicErrorController --> id：basicErrorController（json+白页 适配响应）

  • 处理默认 /error 路径的请求

    ，页面响应

    new ModelAndView("error", model);

    • 容器中有组件

      View

      ->

      id是error

      ；

      • 响应默认错误页

    • 容器中放组件 BeanNameViewResolver（视图解析器）；按照返回的视图名作为组件的id去容器中找View对象。

• 容器中的组件：类型：DefaultErrorViewResolver -> id：conventionErrorViewResolver

  • 如果发生异常错误，会以HTTP的状态码 作为视图页地址（viewName），找到真正的页面

    （主要作用）。

    • error/404、5xx.html
    • 如果想要返回页面，就会找error视图（StaticView默认是一个白页）。

3.异常处理流程

大致流程

1. 执行目标方法，目标方法运行期间有任何异常都会被catch、而且标志当前请求结束；并且用dispatchException

2. 进入视图解析流程（页面渲染？）

   processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

3. mv = processHandlerException; 处理handler发生的异常，处理完成返回ModelAndView;

   • 遍历所有的handlerExceptionResolvers, 看谁能处理当前异常

   HandlerExceptionResolver处理器异常解析器

   

   • 系统默认的 异常解析器；
   • DefaultErrorAttributes先来处理异常。把异常信息保存到rrequest域，并且返回null；

默认没有任何人能处理异常，所以异常会被抛出

1. 如果没有任何人能处理最终底层就会发送/error 请求。会被底层的BasicErrorController处理

2. 解析错误视图；遍历所有的 ErrorViewResolver 看谁能解析。

   

3. 默认的 DefaultErrorViewResolver ,作用是把响应状态码作为错误页的地址拼接成error/500.html

4. 模板引擎最终响应这个页面error/500.html

示例

譬如写一个会抛出异常的控制层：

• 设置controller故意制造异常

@Slf4j
@RestController
public class HelloController {

    @RequestMapping("/hello")
    public String handle01(){
        int i = 1 / 0;//将会抛出ArithmeticException
        log.info("Hello, Spring Boot 2!");
        return "Hello, Spring Boot 2!";
    }
}

当浏览器发出/hello请求，

DispatcherServlet`的`doDispatch()`的`mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

将会抛出ArithmeticException。

方法执行期间抛出任何异常都会被catch , 而且标注定钱请求结束,并且用dispatchException

public class DispatcherServlet extends FrameworkServlet {
    ...
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		...
				// Actually invoke the handler.
            	//将会抛出ArithmeticException
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				applyDefaultViewName(processedRequest, mv);
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
                //将会捕捉ArithmeticException
				dispatchException = ex;
			}
			catch (Throwable err) {
				...
			}
    		//捕捉后，继续运行
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new NestedServletException("Handler processing failed", err));
		}
		finally {
			...
		}
	}

	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				...
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				//ArithmeticException将在这处理
                mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}
		...
	}

	protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
			@Nullable Object handler, Exception ex) throws Exception {

		// Success and error responses may use different content types
		request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		if (this.handlerExceptionResolvers != null) {
            //遍历所有的 handlerExceptionResolvers，看谁能处理当前异常HandlerExceptionResolver处理器异常解析器
			for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
				exMv = resolver.resolveException(request, response, handler, ex);
				if (exMv != null) {
					break;
				}
			}
		}
		...
        //若只有系统的自带的异常解析器（没有自定义的），异常还是会抛出
		throw ex;
	}

}

系统自带的异常解析器：

• DefaultErrorAttributes先来处理异常，它主要功能把异常信息保存到request域，并且返回null。

public class DefaultErrorAttributes implements ErrorAttributes, HandlerExceptionResolver, Ordered {
    ...
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        this.storeErrorAttributes(request, ex);
        return null;
    }

    private void storeErrorAttributes(HttpServletRequest request, Exception ex) {
        request.setAttribute(ERROR_ATTRIBUTE, ex);//把异常信息保存到request域
    }
    ...
    
}    

• 默认没有任何解析器（上图的HandlerExceptionResolverComposite）能处理异常，所以最后异常会被抛出。
• 最终底层就会转发/error 请求。会被底层的BasicErrorController处理。

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {

    @RequestMapping(produces = MediaType.TEXT_HTML_VALUE)
    public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
       HttpStatus status = getStatus(request);
       Map<String, Object> model = Collections
             .unmodifiableMap(getErrorAttributes(request, getErrorAttributeOptions(request, MediaType.TEXT_HTML)));
       response.setStatus(status.value());
       ModelAndView modelAndView = resolveErrorView(request, response, status, model);
       //如果/template/error内没有4**.html或5**.html，
       //modelAndView为空，最终还是返回viewName为error的modelAndView
       return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
    }
    
    ...
}
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    ...
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        ...
     	// Actually invoke the handler.
		mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
		...
        //渲染页面
		processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        ...
    }
    
    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

        boolean errorView = false;
        ...
		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		...
	}
    
    protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
		...

		View view;
		String viewName = mv.getViewName();
		if (viewName != null) {
			// We need to resolve the view name.
            //找出合适error的View，如果/template/error内没有4**.html或5**.html，
            //将会返回默认异常页面ErrorMvcAutoConfiguration.StaticView
            //这里按需深究代码吧！
			view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
			...
		}
		...
		try {
			if (mv.getStatus() != null) {
				response.setStatus(mv.getStatus().value());
			}
            //看下面代码块的StaticView的render块
			view.render(mv.getModelInternal(), request, response);
		}
		catch (Exception ex) {
			...
		}
	}
    
}
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class })
// Load before the main WebMvcAutoConfiguration so that the error View is available
@AutoConfigureBefore(WebMvcAutoConfiguration.class)
@EnableConfigurationProperties({ ServerProperties.class, ResourceProperties.class, WebMvcProperties.class })
public class ErrorMvcAutoConfiguration {
    
    ...
        
   	@Configuration(proxyBeanMethods = false)
	@ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true)
	@Conditional(ErrorTemplateMissingCondition.class)
	protected static class WhitelabelErrorViewConfiguration {

        //将创建一个名为error的系统默认异常页面View的Bean
		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;
		}

	}     
   
    
	private static class StaticView implements View {

		private static final MediaType TEXT_HTML_UTF8 = new MediaType("text", "html", StandardCharsets.UTF_8);

		private static final Log logger = LogFactory.getLog(StaticView.class);

		@Override
		public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response)
				throws Exception {
			if (response.isCommitted()) {
				String message = getMessage(model);
				logger.error(message);
				return;
			}
			response.setContentType(TEXT_HTML_UTF8.toString());
			StringBuilder builder = new StringBuilder();
			Object timestamp = model.get("timestamp");
			Object message = model.get("message");
			Object trace = model.get("trace");
			if (response.getContentType() == null) {
				response.setContentType(getContentType());
			}
            //系统默认异常页面html代码
			builder.append("<html><body><h1>Whitelabel Error Page</h1>").append(
					"<p>This application has no explicit mapping for /error, so you are seeing this as a fallback.</p>")
					.append("<div id='created'>").append(timestamp).append("</div>")
					.append("<div>There was an unexpected error (type=").append(htmlEscape(model.get("error")))
					.append(", status=").append(htmlEscape(model.get("status"))).append(").</div>");
			if (message != null) {
				builder.append("<div>").append(htmlEscape(message)).append("</div>");
			}
			if (trace != null) {
				builder.append("<div style='white-space:pre-wrap;'>").append(htmlEscape(trace)).append("</div>");
			}
			builder.append("</body></html>");
			response.getWriter().append(builder.toString());
		}

		private String htmlEscape(Object input) {
			return (input != null) ? HtmlUtils.htmlEscape(input.toString()) : null;
		}

		private String getMessage(Map<String, ?> model) {
			Object path = model.get("path");
			String message = "Cannot render error page for request [" + path + "]";
			if (model.get("message") != null) {
				message += " and exception [" + model.get("message") + "]";
			}
			message += " as the response has already been committed.";
			message += " As a result, the response may have the wrong status code.";
			return message;
		}

		@Override
		public String getContentType() {
			return "text/html";
		}

	}
}

4.Springboot异常处理的五种方式

1️⃣自定义错误页

• error/404.html error/5xx.html；有精确的错误状态码页面就匹配精确，没有就找 4xx.html；如果都没有就触发白页

注意要在拦截器处放行

2️⃣@ControllerAdvice+@ExceptionHandler处理全局异常

• 底层是 ExceptionHandlerExceptionResolver 支持的

GlobalExceptionHandler.java

@Slf4j
@ControllerAdvice
public class GlobalExceptionHandler { //处理全局异常

    @ExceptionHandler({ArithmeticException.class,NullPointerException.class})  //处理数学运算异常以及空指针异常
    public String handleArithException(Exception e){

        log.error("异常是：{}",e);
        return "login"; //视图地址
    }
}

3️⃣配置 SimpleMappingExceptionResolver 类处理异常

Springboot异常处理的五种方式——SpringBoot学习_lytao123的博客-CSDN博客_springboot异常处理 (gitcode.net)

通过配置 SimpleMappingExceptionResolver 类处理异常也是全局范围的，通过将 SimpleMappingExceptionResolver 类注入到 Spring 容器。

package com.config;

import java.util.Properties;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.handler.SimpleMappingExceptionResolver;

@Configuration
public class GlobalException {
	
	@Bean
	public SimpleMappingExceptionResolver
		getSimpleMappingExceptionResolver(){
		SimpleMappingExceptionResolver resolver = new SimpleMappingExceptionResolver();
		
		Properties mappings = new Properties();
		/*
		 * 参数一：异常的类型，注意必须是异常类型的全名
		 * 参数二：视图名称
		 */
		mappings.put("java.lang.ArithmeticException", "errors");
		
		//设置异常与视图映射信息的
		resolver.setExceptionMappings(mappings);
		
		return resolver;
	}
}

注意：在类上加上 @Configuration 注解，在方法上加上 @Bean 注解，方法返回值必须是 SimpleMappingExceptionResolver 。

编写 errors.html 页面

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>自定义 springboot 异常处理页面</title>
</head>
<body>
配置 SimpleMappingExceptionResolver 类处理异常
</body>
</html>
12345678910

访问 http://localhost:8080/exceptionMethod 链接后抛出 ArithmeticException 异常，跳转到 errors.html 页面，效果图如下所示：

@ResponseStatus自定义异常

• 底层是 ResponseStatusExceptionResolver ，
• 把responsestatus注解的信息底层调用response.sendError(statusCode, resolvedReason);tomcat发送的/error

UserTooManyException.java

@ResponseStatus(value= HttpStatus.FORBIDDEN,reason = "用户数量太多")
public class UserTooManyException extends RuntimeException {

    public  UserTooManyException(){

    }
    public  UserTooManyException(String message){
        super(message);
    }
}

TableController.java

@Controller
public class TableController {
    .....
        
    @GetMapping("/dynamic_table")
    public String dynamic_table(Model model) throws UserTooManyException {
        // 表格内容的遍历
        List<User> users = Arrays.asList(new User("Vsa", "3423443"), new User("Ads", "3erwefg12"),
                new User("BSd", "rw5efg12"), new User("Arq", "3454343"));

        model.addAttribute("users",users);
        if(users.size()>=3){
            throw new UserTooManyException("overMaxSession");
        }
        return "table/dynamic_table";
    }
    ....
        
}

Spring底层的异常

如 参数 类型转换异常

• DefaultHandlerExceptionResolver 处理框架底层的异常。
• response.sendError(HttpServletResponse.SC_BAD_REQUEST, ex.getMessage());

如果不处理 , 就会显示Tomcat默认的错误页

4️⃣自定义实现HandlerExceptionResolver处理异常

• 可以作为默认的全局异常处理规则

@Order(value= Ordered.HIGHEST_PRECEDENCE)  //优先级，数字越小优先级越高
@Component
public class CustomerHandlerExceptionResolver implements HandlerExceptionResolver {

    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {

        try {
            response.sendError(521,"The error I liked");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return  new ModelAndView();
    }
}

5️⃣ErrorViewResolver 实现自定义处理异常

ErrorViewResolver 实现自定义处理异常

• response.sendError()，error请求就会转给controller
• 你的异常没有任何人能处理，tomcat底层调用response.sendError()，error请求就会转给controller
• basicErrorController 要去的页面地址是 ErrorViewResolver

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {

    ...
    
	@RequestMapping(produces = MediaType.TEXT_HTML_VALUE)
	public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
		HttpStatus status = getStatus(request);
		Map<String, Object> model = Collections
				.unmodifiableMap(getErrorAttributes(request, getErrorAttributeOptions(request, MediaType.TEXT_HTML)));
		response.setStatus(status.value());
		ModelAndView modelAndView = resolveErrorView(request, response, status, model);
		return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
	}
    
    protected ModelAndView resolveErrorView(HttpServletRequest request, HttpServletResponse response, HttpStatus status,
			Map<String, Object> model) {
        //这里用到ErrorViewResolver接口
		for (ErrorViewResolver resolver : this.errorViewResolvers) {
			ModelAndView modelAndView = resolver.resolveErrorView(request, status, model);
			if (modelAndView != null) {
				return modelAndView;
			}
		}
		return null;
	}
    
    ...
    
}

ErrorViewResolver.java

@FunctionalInterface
public interface ErrorViewResolver {

	ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model);

}

9、原生组件注入

• Servlet
• Filter
• Listener

1.原生注解与Spring方式注入

官方文档 - Servlets, Filters, and listeners

使用Servlet API

@ServletComponentScan(basePackages = {"pers.dhx_.admin"})指定原生的Servlet在哪里

@WebServlet("/mySerlvet")
@WebFilter
@WebListener

MyServlet.java

@WebServlet(urlPatterns = "/my")
public class MyServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("66666");
    }
}

注意需要在application类里面加上@ServletComponentScan 让springboot吧我们写的Servlet扫描进去

@ServletComponentScan(basePackages = {"pers.dhx_.admin"}) // 可以自动将我们写的servlet扫描进来
@SpringBootApplication
public class Demo04AdminApplication {
    public static void main(String[] args) {
        SpringApplication.run(Demo04AdminApplication.class, args);
    }
}

MyFilter.java

@Slf4j
@WebFilter(urlPatterns = {"/css/*","/images/*"})// 单个*是Servlet的写法,/**是spring里面的写法
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("Filter init");
        Filter.super.init(filterConfig);
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("Filter working");
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {
        log.info("Filter destroy");
        Filter.super.destroy();
    }
}

MyServletContextListener.java

@Slf4j
@WebListener
public class MyServletContextListener implements ServletContextListener {


    @Override
    public void contextInitialized(ServletContextEvent sce) {
        log.info("MySwervletContextListener监听到项目初始化完成");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        log.info("MySwervletContextListener监听到项目销毁");
    }
}

最后还要在主启动类添加注解@ServletComponentScan

@ServletComponentScan(basePackages = "com.lun")//
@SpringBootApplication(exclude = RedisAutoConfiguration.class)
public class Boot05WebAdminApplication {

    public static void main(String[] args) {
        SpringApplication.run(Boot05WebAdminApplication.class, args);
    }
}

如果多个Servlet都能处理到同一层路径, 按照精确优先原则

比如当前有DispatcherServlet 以及 MyServlet 分别接收 / 以及 /my ,

如果我们发送/my请求, 那么这个请求就会优先交给MyServlet来处理

Spring方式注入

使用RegistrationBean

Spring Boot提供的针对Servlet 3.0+容器的注册bean基类。

该类的目的是用于向Servlet容器(Tomcat,Jetty等)注册工作组件，比如Servlet,Filter或者EventListener。

这是一个抽象基类，实现了接口ServletContextInitializer。ServletContextInitializer约定了当前RegistrationBean会在Servlet启动时被调用方法#onStartup。

该抽象基类提供了如下功能:

1. 当前注册bean的优先级，通过属性order指定，缺省值为最低优先级Ordered.LOWEST_PRECEDENCE。
2. 当前注册bean是否被禁用，通过属性enabled指定。如果被禁用,Servlet容器启动时并不执行该注册bean的注册动作。缺省值为true。
3. 通过抽象方法的方式约定了实现子类必须实现某些功能，比如具体注册什么以及具体的注册逻辑都必须由子类实现提供。

• ServletRegistrationBean
• FilterRegistrationBean
• ServletListenerRegistrationBean

proxyBeanMethods = true 表示这个配置类被代理了，false则不被代理。

当为true时，你无论调用几次，它永远上是同一个对象。

@Configuration(proxyBeanMethods = true) //
public class MyRegistConfig {

    @Bean
    public ServletRegistrationBean myServlet(){
        MyServlet myServlet = new MyServlet();

        return new ServletRegistrationBean(myServlet,"/my","/my02");
    }

    @Bean
    public FilterRegistrationBean myFilter(){

        MyFilter myFilter = new MyFilter();
//        return new FilterRegistrationBean(myFilter,myServlet());
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(myFilter);
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/my","/css/*"));
        return filterRegistrationBean;
    }

    @Bean
    public ServletListenerRegistrationBean myListener(){
        MyServletContextListener mySwervletContextListener = new MyServletContextListener();
        return new ServletListenerRegistrationBean(mySwervletContextListener);
    }
}

2.DispatcherServlet注入原理

org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration配置类

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {
	/*
	 * The bean name for a DispatcherServlet that will be mapped to the root URL "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";

	/*
	 * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

	@Configuration(proxyBeanMethods = false)
	@Conditional(DefaultDispatcherServletCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	protected static class DispatcherServletConfiguration {

        //创建DispatcherServlet类的Bean
		@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
			DispatcherServlet dispatcherServlet = new DispatcherServlet();
			dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
			dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
			dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
			dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
			dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
			return dispatcherServlet;
		}

		@Bean
		@ConditionalOnBean(MultipartResolver.class)
		@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
		public MultipartResolver multipartResolver(MultipartResolver resolver) {
			// Detect if the user has created a MultipartResolver but named it incorrectly
			return resolver;
		}

	}
    
    @Configuration(proxyBeanMethods = false)
	@Conditional(DispatcherServletRegistrationCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	@Import(DispatcherServletConfiguration.class)
	protected static class DispatcherServletRegistrationConfiguration {

        //注册DispatcherServlet类
		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
		@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
				WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
			DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
					webMvcProperties.getServlet().getPath());
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}

	}
    
    ...
    
}

DispatcherServlet默认映射的是 / 路径，可以通过在配置文件修改spring.mvc.servlet.path=/mvc。

10、嵌入式Servlet容器

1.切换web服务器与定制化

• 默认支持的WebServer

  • Tomcat, Jetty, or Undertow。
  • ServletWebServerApplicationContext容器启动寻找ServletWebServerFactory 并引导创建服务器。

• 原理

  • SpringBoot应用启动发现当前是Web应用，web场景包-导入tomcat。

  • web应用会创建一个web版的IOC容器 ServletWebServerApplicationContext 。

  • ServletWebServerApplicationContext 启动的时候寻找 ServletWebServerFactory （Servlet 的web服务器工厂——>Servlet 的web服务器）。

  • SpringBoot底层默认有很多的WebServer工厂（

    ServletWebServerFactoryConfiguration

    内创建Bean），如：

    • TomcatServletWebServerFactory
    • JettyServletWebServerFactory
    • UndertowServletWebServerFactory

  • 底层直接会有一个自动配置类ServletWebServerFactoryAutoConfiguration。

  • ServletWebServerFactoryAutoConfiguration导入了ServletWebServerFactoryConfiguration（配置类）。

  • ServletWebServerFactoryConfiguration根据动态判断系统中到底导入了那个Web服务器的包。（默认是web-starter导入tomcat包），容器中就有 TomcatServletWebServerFactory

  • TomcatServletWebServerFactory创建出Tomcat服务器并启动；TomcatWebServer 的构造器拥有初始化方法initialize——this.tomcat.start();

内嵌服务器，与以前手动把启动服务器相比，改成现在使用代码启动（tomcat核心jar包存在）。

Spring Boot默认使用Tomcat服务器，若需更改其他服务器，则修改工程pom.xml：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

官方文档 - Use Another Web Server

2.定制Servlet容器

• 实现WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>
• • 把配置文件的值和ServletWebServerFactory进行绑定
• 修改配置文件 server.xxx
• 直接自定义 ConfigurableServletWebServerFactory

xxxxxCustomizer：定制化器，可以改变xxxx的默认规则

import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.stereotype.Component;

@Component
public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

    @Override
    public void customize(ConfigurableServletWebServerFactory server) {
        server.setPort(9000);
    }

}

11、定制化原理

• SpringBoot定制化组件的几种方式（小结）

定制化的常见方式

1. 修改配置文件

2. xxxxxCustomizer

3. 编写自定义的配置类 xxxConfiguration + @Bean替换、增加容器中默认组件，视图解析器

4. Web应用 编写一个配置类实现 WebMvcConfigurer 即可定制化web功能 + @Bean给容器中再扩展一些组件

   一般就是这样写

   @Configuration
   public class AdminWebConfig implements WebMvcConfigurer{
   }

5. @EnableWebMvc + WebMvcConfigurer — @Bean 可以全面接管SpringMVC，所有规则全部自己重新配置；

实现定制和扩展功能（高级功能，初学者退避三舍）。

@EnableWebMvc其实就是把默认的都禁用了, 原本的自动装配, 静态资源, 视图解析器等等都需要自己去配置

• 原理：

  1. WebMvcAutoConfiguration : 默认的SpringMVC的自动配置功能类，如静态资源、欢迎页、视图解析器等。

  2. 一旦使用 @EnableWebMvc ，会@Import(DelegatingWebMvcConfiguration.class)。

  3. DelegatingWebMvcConfiguration
     

     的作用，只保证SpringMVC最基本的使用

     • 把所有系统中的WebMvcConfigurer拿过来，所有功能的定制都是这些WebMvcConfigurer合起来一起生效。
     • 自动配置了一些非常底层的组件，如RequestMappingHandlerMapping，这些组件依赖的组件都是从容器中获取如。
     • public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport。

  4. WebMvcAutoConfiguration里面的配置要能生效必须 @ConditionalOnMissingBean(WebMvcConfigurationSupport.class)。

  5. @EnableWebMvc 导致了WebMvcAutoConfiguration 没有生效。

原理分析套路

场景starter - >xxxxAutoConfiguration - >导入xxx组件 - >绑定xxxProperties -> 绑定配置文件项

默认情况下 , 我们不需要做任何修改, 只依靠修改配置文件, 就可以使用springboot