如果在請求映射期間發(fā)生異常或從請求處理程序(例如@Controller)拋出異常，DispatcherServlet將委托給HandlerExceptionResolver bean鏈來解決異常并提供替代處理，這通常是一個錯誤響應。
概述
如果在請求映射期間發(fā)生異?；驈恼埱筇幚沓绦?例如@Controller)拋出異常，DispatcherServlet將委托給HandlerExceptionResolver
下表列出了可用的HandlerExceptionResolver實現(xiàn)：
HandlerExceptionResolver | 描述 |
SimpleMappingExceptionResolver | 異常類名和錯誤視圖名之間的映射。用于在瀏覽器應用程序中渲染錯誤頁面。 |
DefaultHandlerExceptionResolver | 解析Spring MVC引發(fā)的異常，并將其映射為HTTP狀態(tài)碼。另見可選的ResponseEntityExceptionHandler和REST API異常。 |
ResponseStatusExceptionResolver | 使用@ResponseStatus注解解析異常，并根據(jù)注解中的值將異常映射為HTTP狀態(tài)碼。 |
ExceptionHandlerExceptionResolver | 通過在@Controller或@ControllerAdvice類中調用@ExceptionHandler方法來解決異常。 |
異常解析器鏈
你可以在Spring配置中聲明多個HandlerExceptionResolver
HandlerExceptionResolver的約定規(guī)定它可以返回:
- 指向錯誤視圖的ModelAndView
- 如果異常是在解析器中處理的，則返回空的ModelAndView
- 如果異常仍然未解決，則為null，以便后續(xù)的解析器嘗試，如果異常在最后仍然存在，則允許它向上冒泡到Servlet容器。
MVC配置自動為默認的Spring MVC異常、@ResponseStatus注解的異常以及@ExceptionHandler方法聲明了內置的解析器。
容器錯誤頁配置
如果任何HandlerExceptionResolver都無法解決異常，因此需要傳播，或者響應狀態(tài)被設置為錯誤狀態(tài)(即4xx、5xx)， Servlet容器可以在HTML中渲染一個默認的錯誤頁面。要定制容器的默認錯誤頁面，可以在web.xml中聲明錯誤頁面映射。如下面的例子所示:?
<error-page>
<location>/error</location>
</error-page>
根據(jù)前面的示例，當出現(xiàn)異常冒泡或響應具有錯誤狀態(tài)時，Servlet容器將在容器中向配置的URL(例如/error)發(fā)送錯誤。然后由DispatcherServlet處理，可能會將其映射到一個@Controller，這個@Controller可以實現(xiàn)為返回一個帶有模型的錯誤視圖名稱，或者渲染一個JSON響應，如下面的例子所示:?
@RestController
public class ErrorController {
@RequestMapping(path = "/error")
public Map<String, Object> handle(HttpServletRequest request) {
Map<String, Object> map = new HashMap<String, Object>();
map.put("status", request.getAttribute("javax.servlet.error.status_code"));
map.put("reason", request.getAttribute("javax.servlet.error.message"));
return map;
}
}
錯誤處理原理
public class DispatcherServlet {
// 取得容器中所有的異常解析器
private List<HandlerExceptionResolver> handlerExceptionResolvers;
protected void initStrategies(ApplicationContext context) {
// 初始化異常解析器
initHandlerExceptionResolvers(context);
}
private void initHandlerExceptionResolvers(ApplicationContext context) {
this.handlerExceptionResolvers = null;
if (this.detectAllHandlerExceptionResolvers) {
// 獲取容器中所有的異常解析器
Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
}
}
}
}發(fā)生異常后邏輯處理?
public class DispatcherServlet {
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
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;
// 判斷當前調用是否發(fā)生了異常
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
} else {
// 獲取當前處理句柄HandlerMethod
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
// 處理異常
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
if (mv != null && !mv.wasCleared()) {
render(mv, request, response);
}
}
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
@Nullable Object handler, Exception ex) throws Exception {
request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
ModelAndView exMv = null;
if (this.handlerExceptionResolvers != null) {
// 遍歷在上面初始化查找到的所有異常解析器
for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
// 執(zhí)行異常解析
exMv = resolver.resolveException(request, response, handler, ex);
if (exMv != null) {
break;
}
}
}
if (exMv != null) {
// ...
return exMv ;
}
// 如果所有的異常解析器都返回null，則直接拋出異常，該異常會被Servlet進行處理
throw ex ;
}
}異常解析器默認配置
public class WebMvcAutoConfiguration {
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(WebProperties.class)
public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration {
}
}
public class WebMvcConfigurationSupport {
@Bean
public HandlerExceptionResolver handlerExceptionResolver(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager) {
List<HandlerExceptionResolver> exceptionResolvers = new ArrayList<>();
// 處理自定義異常解析器的配置
configureHandlerExceptionResolvers(exceptionResolvers);
if (exceptionResolvers.isEmpty()) {
// 如果沒有異常解析器，那么添加默認的異常解析器
addDefaultHandlerExceptionResolvers(exceptionResolvers, contentNegotiationManager);
}
extendHandlerExceptionResolvers(exceptionResolvers);
HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();
// 設置高優(yōu)先級，Composite成為統(tǒng)一的入口
composite.setOrder(0);
composite.setExceptionResolvers(exceptionResolvers);
return composite;
}
// 默認配置
protected final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers, ContentNegotiationManager mvcContentNegotiationManager) {
ExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();
exceptionHandlerResolver.setContentNegotiationManager(mvcContentNegotiationManager);
exceptionHandlerResolver.setMessageConverters(getMessageConverters());
exceptionHandlerResolver.setCustomArgumentResolvers(getArgumentResolvers());
exceptionHandlerResolver.setCustomReturnValueHandlers(getReturnValueHandlers());
if (jackson2Present) {
exceptionHandlerResolver.setResponseBodyAdvice(Collections.singletonList(new JsonViewResponseBodyAdvice()));
}
if (this.applicationContext != null) {
exceptionHandlerResolver.setApplicationContext(this.applicationContext);
}
exceptionHandlerResolver.afterPropertiesSet();
exceptionResolvers.add(exceptionHandlerResolver);
ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();
responseStatusResolver.setMessageSource(this.applicationContext);
exceptionResolvers.add(responseStatusResolver);
exceptionResolvers.add(new DefaultHandlerExceptionResolver());
}
}完畢?。?！
