Java深入 - Spring 异常处理HandlerExceptionResolver

Spring的异常统一处理非常简单，首先我们需要看一下Spring中定义的HandlerExceptionResolver接口：

/** * Interface to be implemented by objects than can resolve exceptions thrown * during handler mapping or execution, in the typical case to error views. * Implementors are typically registered as beans in the application context. * * <p>Error views are analogous to the error page JSPs, but can be used with * any kind of exception including any checked exception, with potentially * fine-granular mappings for specific handlers. * * @author Juergen Hoeller * @since 22.11.2003 */public interface HandlerExceptionResolver {/** * Try to resolve the given exception that got thrown during on handler execution, * returning a ModelAndView that represents a specific error page if appropriate. * <p>The returned ModelAndView may be {@linkplain ModelAndView#isEmpty() empty} * to indicate that the exception has been resolved successfully but that no view * should be rendered, for instance by setting a status code. * @param request current HTTP request * @param response current HTTP response * @param handler the executed handler, or <code>null</code> if none chosen at the * time of the exception (for example, if multipart resolution failed) * @param ex the exception that got thrown during handler execution * @return a corresponding ModelAndView to forward to, * or <code>null</code> for default processing */ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex);}

他定义了一个resolveException方法，我们如果要处理异常的话，需要实现这个接口类，并且实现resolveException方法，在resolveException方法中处理自己的异常逻辑。

例如我设计一个自定义的异常处理类：

/** * 自定义一个异常捕获处理类 * @author zhuli * @date 2014-9-3 */public class MyExceptionResolver implements HandlerExceptionResolver {    private static final Logger logger = LoggerFactory.getLogger(MyExceptionResolver.class);    @Override    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {                //可以自由处理各种异常逻辑        if (ex instanceof org.springframework.web.HttpRequestMethodNotSupportedException) {            logger.warn(Logger.ACTION.DEFAULT, "Http Method Error");        }        return null;    }}

然后需要将我们的我们自定义的MyExceptionResolver类注入到bean中

<bean id="MyExceptionResolver" class="com.tiantian.xxx.web.handler.MyExceptionResolver"/>

具体Spring是怎么调用的？我们可以先看下Spring中的doDispatch方法中，有这么一段代码：

catch (ModelAndViewDefiningException ex) {logger.debug("ModelAndViewDefiningException encountered", ex);mv = ex.getModelAndView();}catch (Exception ex) {Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);mv = processHandlerException(processedRequest, response, handler, ex);errorView = (mv != null);}

其中processHandlerException方法就是来捕获异常处理的，那么继续看processHandlerException这个方法：

protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,Object handler, Exception ex) throws Exception {// Check registered HandlerExceptionResolvers...ModelAndView exMv = null;for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);if (exMv != null) {break;}}if (exMv != null) {if (exMv.isEmpty()) {return null;}// We might still need view name translation for a plain error model...if (!exMv.hasView()) {exMv.setViewName(getDefaultViewName(request));}if (logger.isDebugEnabled()) {logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);}WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());return exMv;}throw ex;}

这个方法中的handlerExceptionResolver.resolveException就是用来捕获异常的，并且Spring允许多个自定义的异常类实现。

可以看this.handlerExceptionResolvers方法，跟踪进去

private void initHandlerExceptionResolvers(ApplicationContext context) {this.handlerExceptionResolvers = null;if (this.detectAllHandlerExceptionResolvers) {// Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);if (!matchingBeans.isEmpty()) {this.handlerExceptionResolvers = new ArrayList<HandlerExceptionResolver>(matchingBeans.values());// We keep HandlerExceptionResolvers in sorted order.OrderComparator.sort(this.handlerExceptionResolvers);}}else {try {HandlerExceptionResolver her =context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);this.handlerExceptionResolvers = Collections.singletonList(her);}catch (NoSuchBeanDefinitionException ex) {// Ignore, no HandlerExceptionResolver is fine too.}}// Ensure we have at least some HandlerExceptionResolvers, by registering// default HandlerExceptionResolvers if no other resolvers are found.if (this.handlerExceptionResolvers == null) {this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);if (logger.isDebugEnabled()) {logger.debug("No HandlerExceptionResolvers found in servlet '" + getServletName() + "': using default");}}}

可以清洗看到这个方法是将handlerExceptionResolvers进行了初始化，并将自定义的异常处理类（可以多个）写入this.handlerExceptionResolvers