错误处理-SpringBoot默认错误处理机制-【源码分析】底层组件功能分析

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

  • 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

错误处理-【源码分析】底层组件功能分析

  • 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)。

错误处理-【源码流程】异常处理流程

譬如写一个会抛出异常的控制层:
···java
@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,DispatcherServletdoDispatch()mv = ha.handle(processedRequest, response, mappedHandler.getHandler());将会抛出ArithmeticException

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
错误处理-SpringBoot默认错误处理机制-【源码分析】底层组件功能分析_第1张图片
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("

Whitelabel Error Page

"
).append( "

This application has no explicit mapping for /error, so you are seeing this as a fallback.

"
) .append("
").append(timestamp).append("
"
) .append("
There was an unexpected error (type=").append(htmlEscape(model.get("error"))) .append(", status=").append(htmlEscape(model.get("status"))).append(").
"
); if (message != null) { builder.append("
").append(htmlEscape(message)).append("
"
); } if (trace != null) { builder.append("
").append(htmlEscape(trace)).append("
"
); } builder.append(""); 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"; } } }

错误处理-【源码流程】几种异常处理原理

  • 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
  • @ControllerAdvice+@ExceptionHandler处理全局异常;底层是 ExceptionHandlerExceptionResolver 支持的

@Slf4j
@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler({ArithmeticException.class,NullPointerException.class})  //处理异常
    public String handleArithException(Exception e){

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

@ResponseStatus+自定义异常 ;底层是 ResponseStatusExceptionResolver ,把responseStatus注解的信息底层- response.sendError(statusCode, resolvedReason),tomcat发送的/error

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

    public  UserTooManyException(){

    }
    public  UserTooManyException(String message){
        super(message);
    }
}
@Controller
public class TableController {
    
	@GetMapping("/dynamic_table")
    public String dynamic_table(@RequestParam(value="pn",defaultValue = "1") Integer pn,Model model){
        //表格内容的遍历
	     List<User> users = Arrays.asList(new User("zhangsan", "123456"),
                new User("lisi", "123444"),
                new User("haha", "aaaaa"),
                new User("hehe ", "aaddd"));
        model.addAttribute("users",users);

        if(users.size()>3){
            throw new UserTooManyException();//抛出自定义异常
        }
        return "table/dynamic_table";
    }
    
}
```@Controller
public class TableController {
    
	@GetMapping("/dynamic_table")
    public String dynamic_table(@RequestParam(value="pn",defaultValue = "1") Integer pn,Model model){
        //表格内容的遍历
	     List<User> users = Arrays.asList(new User("zhangsan", "123456"),
                new User("lisi", "123444"),
                new User("haha", "aaaaa"),
                new User("hehe ", "aaddd"));
        model.addAttribute("users",users);

        if(users.size()>3){
            throw new UserTooManyException();//抛出自定义异常
        }
        return "table/dynamic_table";
    }
    
}
  • Spring自家异常如 org.springframework.web.bind.MissingServletRequestParameterExceptionDefaultHandlerExceptionResolver 处理Spring自家异常。

    • response.sendError(HttpServletResponse.SC_BAD_REQUEST/*400*/, ex.getMessage());
  • 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(511,"我喜欢的错误");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return new ModelAndView();
    }
}
  • 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;
	}
    
    ...
    
}
@FunctionalInterface
public interface ErrorViewResolver {

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

}

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