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：

public interface HandlerExceptionResolver {
ModelAndView resolveException(
HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex);

}

handler 应该就是 controller ，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