环境：Springboot3.0.5

概述

如果在请求映射期间发生异常或从请求处理程序(例如@Controller)抛出异常，DispatcherServlet将委托给HandlerExceptionResolver

(资料图片)

下表列出了可用的HandlerExceptionResolver实现。

HandlerExceptionResolver实现类:

HandlerExceptionResolver	描述
SimpleMappingExceptionResolver	异常类名和错误视图名之间的映射。用于在浏览器应用程序中渲染错误页面。
DefaultHandlerExceptionResolver	解析Spring MVC引发的异常，并将其映射为HTTP状态码。
ResponseStatusExceptionResolver	使用@ResponseStatus注解解析异常，并根据注解中的值将异常映射为HTTP状态码。
ExceptionHandlerExceptionResolver	通过在@Controller或@ControllerAdvice类中调用由@ExceptionHandler注释的方法来解决异常。

我们可以声明多个HandlerExceptionResolver

HandlerExceptionResolver的约定规定它可以返回:

指向错误视图的ModelAndView。如果异常是在解析器中处理的，则返回空的ModelAndView。如果异常仍然未解决，则为null，以便后续的解析器尝试，如果异常在最后仍然存在，则允许它向上冒泡到Servlet容器。Controller接口调用原理

SpringMVC请求入口通过DispatcherServlet执行大致核心流程如下：

首先通过HandlerMapping确定目标Handler对象（如果接口是Controller那么这里会是HandlerMethod）通过上一步Handler对象，确定执行真正调用的HandlerAdapter

这里以Controller接口为例，HandlerAdapter对象为RequestMappingHandlerAdapter

DispatcherServlet

public class DispatcherServlet extends FrameworkServlet {  protected void doDispatch(...) throws Exception {    HandlerExecutionChain mappedHandler = null;    try {      Exception dispatchException = null;      // 根据请求确定Handler对象（遍历所有的HandlerMapping）      mappedHandler = getHandler(processedRequest);      // 根据上一步确定的Handler对象，确定HandlerAdapter对象      HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());      // 真正执行目标方法的调用      mv = ha.handle(processedRequest, response, mappedHandler.getHandler());    } catch (Exception ex) {      dispatchException = ex;    } catch (Throwable err) {      dispatchException = new ServletException("Handler dispatch failed: " + err, err);    }    processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);  }}

RequestMappingHandlerAdapter

public class RequestMappingHandlerAdapter {  protected ModelAndView handleInternal(...) throws Exception {    ModelAndView mav;    mav = invokeHandlerMethod(request, response, handlerMethod);  }  protected ModelAndView invokeHandlerMethod(...) throws Exception {    // ...    ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);    // ... 对ServletInvocableHandlerMethod进行配置    invocableMethod.invokeAndHandle(webRequest, mavContainer);    return getModelAndView(mavContainer, modelFactory, webRequest);  }}

ServletInvocableHandlerMethod执行参数解析目标Controller方法调用及返回值的处理

public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {  public void invokeAndHandle(...) throws Exception {    // 该方法中会进行请求参数的解析及目标方法的调用    Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);    // ...    try {      // 处理返回值      this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);    } catch (Exception ex) {      throw ex;    }  }}

通过上面的源码分析，在调用过程中如果发生了异常会将异常直接抛出，在DispatcherServlet中会进行异常的处理。

异常解析原理分析

接着上面的源码分析，当发生异常后最终会在DispatcherServlet#processDispatchResult方法中进行处理。

public class DispatcherServlet extends FrameworkServlet {  /*    * 默认情况下有如下2个异常解析器    * 1. DefaultErrorAttributes    * 2. ExceptionHandlerExceptionResolver    */  private List handlerExceptionResolvers;  private void processDispatchResult(...) {    if (exception != null) {      Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);      // 处理异常      mv = processHandlerException(request, response, handler, exception);    }  }  protected ModelAndView processHandlerException(...) throws Exception {    ModelAndView exMv = null;    if (this.handlerExceptionResolvers != null) {      // 遍历所有的异常解析器      for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {        // 解析异常，核心的解析器是ExceptionHandlerExceptionResolver        exMv = resolver.resolveException(request, response, handler, ex);      }    }    // ...  }}

ExceptionHandlerExceptionResolver类继承自AbstractHandlerMethodExceptionResolver该类又继承自AbstractHandlerExceptionResolver

// 调用父类(AbstractHandlerExceptionResolver)方法public abstract class AbstractHandlerExceptionResolver implements HandlerExceptionResolver, Ordered {  public ModelAndView resolveException(...) {    // doResolveException该方法在子类AbstractHandlerMethodExceptionResolver中重写    ModelAndView result = doResolveException(request, response, handler, ex);  }}

AbstractHandlerMethodExceptionResolver

public abstract class AbstractHandlerMethodExceptionResolver extends AbstractHandlerExceptionResolver {  protected final ModelAndView doResolveException(...) {    HandlerMethod handlerMethod = (handler instanceof HandlerMethod hm ? hm : null);    return doResolveHandlerMethodException(request, response, handlerMethod, ex);  }}

ExceptionHandlerExceptionResolver

public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExceptionResolver implements ApplicationContextAware, InitializingBean {  protected ModelAndView doResolveHandlerMethodException(...) {    // 该方法中会先从当前的Controller中查找是否有@ExceptionHandler注解的方法（如果匹配）    // 如果没有再从全局的异常处理类句柄中查找    ServletInvocableHandlerMethod exceptionHandlerMethod = getExceptionHandlerMethod(handlerMethod, exception);    if (exceptionHandlerMethod == null) {      return null;    }    // 执行异常处理方法的调用    exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, arguments);  }  protected ServletInvocableHandlerMethod getExceptionHandlerMethod(...) {    Class handlerType = null;    if (handlerMethod != null) {        handlerType = handlerMethod.getBeanType();      // 缓存并设置当前执行Class对应的ExceptionHandlerMethodResolver      // ExceptionHandlerMethodResolver构造函数中会解析当前类中的所有方法是否有@ExceptionHandler注解      ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.computeIfAbsent(handlerType, ExceptionHandlerMethodResolver::new);      // 解析是否匹配当前发生的异常      Method method = resolver.resolveMethod(exception);      if (method != null) {        return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method, this.applicationContext);      }    }    // 如果上面的执行的Class中没有找到对应处理器，那么就从全局的异常处理中进行查找匹配    // 这里的exceptionHandlerAdviceCache集合在类初始化执行时已经处理完成    for (Map.Entry entry : this.exceptionHandlerAdviceCache.entrySet()) {      ControllerAdviceBean advice = entry.getKey();      if (advice.isApplicableToBeanType(handlerType)) {        ExceptionHandlerMethodResolver resolver = entry.getValue();        Method method = resolver.resolveMethod(exception);        if (method != null) {          return new ServletInvocableHandlerMethod(advice.resolveBean(), method, this.applicationContext);        }      }    }    return null;  }}

通过上面的源码分析你应该知道了关于SpringMVC中异常处理的原理。

当上面的异常处理机制都没法处理，那么将会调用默认的/error接口。

public class ErrorMvcAutoConfiguration {  @Bean  @ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)  public BasicErrorController basicErrorController(ErrorAttributes errorAttributes, ObjectProvider errorViewResolvers) {    return new BasicErrorController(errorAttributes, this.serverProperties.getError(), errorViewResolvers.orderedStream().toList());  }  }

BasicErrorController

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

上面的错误接口/error在容器启动时会自动注册到内嵌的容器中，如：Tomcat。