当前SpringMVC非常流行，在大多数情况，我们都需要自定义一些错误页面（例如：401， 402， 403， 500…），以便更友好的提示。对于spring mvc，这些当然是支持自定义的，spring是怎么做的？ 还是去看看spring的源码吧：
原理
DispatcherServlet
众所周知，springmvc的入口是DispatcherServlet, 在DispatcherServlet的源码中，不知你是否注意到了以下方法：
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()) {
request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
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;
}
这个方法就是springmvc对于异常的处理，其调用了HandlerExceptionResolver的resolveException方法。HandlerExceptionResolver有众多实现类，其中，重点看看
SimpleMappingExceptionResolver（我们就是要通过它来配置自定义错误页面）。
SimpleMappingExceptionResolver
public class SimpleMappingExceptionResolver extends AbstractHandlerExceptionResolver {
...
private Properties exceptionMappings;
private Class<?>[] excludedExceptions;
private Map<String, Integer> statusCodes = new HashMap<String, Integer>();
...
public void setExceptionMappings(Properties mappings) {
this.exceptionMappings = mappings;
}
public void setStatusCodes(Properties statusCodes) {
for (Enumeration<?> enumeration = statusCodes.propertyNames(); enumeration.hasMoreElements();) {
String viewName = (String) enumeration.nextElement();
Integer statusCode = new Integer(statusCodes.getProperty(viewName));
this.statusCodes.put(viewName, statusCode);
}
}
}
@Override
protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response,
Object handler, Exception ex) {
// Expose ModelAndView for chosen error view.
String viewName = determineViewName(ex, request);
if (viewName != null) {
// Apply HTTP status code for error views, if specified.
// Only apply it if we're processing a top-level request.
Integer statusCode = determineStatusCode(request, viewName);
if (statusCode != null) {
applyStatusCodeIfPossible(request, response, statusCode);
}
return getModelAndView(viewName, ex, request);
}
else {
return null;
}
}
protected String determineViewName(Exception ex, HttpServletRequest request) {
String viewName = null;
if (this.excludedExceptions != null) {
for (Class<?> excludedEx : this.excludedExceptions) {
if (excludedEx.equals(ex.getClass())) {
return null;
}
}
}
// Check for specific exception mappings.
if (this.exceptionMappings != null) {
viewName = findMatchingViewName(this.exceptionMappings, ex);
}
// Return default error view else, if defined.
if (viewName == null && this.defaultErrorView != null) {
if (logger.isDebugEnabled()) {
logger.debug("Resolving to default view '" + this.defaultErrorView + "' for exception of type [" +
ex.getClass().getName() + "]");
}
viewName = this.defaultErrorView;
}
return viewName;
}
protected String findMatchingViewName(Properties exceptionMappings, Exception ex) {
String viewName = null;
String dominantMapping = null;
int deepest = Integer.MAX_VALUE;
for (Enumeration<?> names = exceptionMappings.propertyNames(); names.hasMoreElements();) {
String exceptionMapping = (String) names.nextElement();
int depth = getDepth(exceptionMapping, ex);
if (depth >= 0 && (depth < deepest || (depth == deepest &&
dominantMapping != null && exceptionMapping.length() > dominantMapping.length()))) {
deepest = depth;
dominantMapping = exceptionMapping;
viewName = exceptionMappings.getProperty(exceptionMapping);
}
}
if (viewName != null && logger.isDebugEnabled()) {
logger.debug("Resolving to view '" + viewName + "' for exception of type [" + ex.getClass().getName() +
"], based on exception mapping [" + dominantMapping + "]");
}
return viewName;
}
protected Integer determineStatusCode(HttpServletRequest request, String viewName) {
if (this.statusCodes.containsKey(viewName)) {
return this.statusCodes.get(viewName);
}
return this.defaultStatusCode;
}
由此可见：
SimpleMappingExceptionResolver通过 exceptionMappings和statusCodes来确立Exception、http状态码以及view之间的映射关系。明白这个就很简单了，我们可以通过设置exceptionMappings、statusCodes的值来实现我们自定义的映射关系。
实战
页面准备
我们在WEB-INF/views/commons/error（目录自己定）新建我们自定义的错误页面，404.html, 500.html等等。
