spring3.0异常处理进阶

spring3.0开发不可避免要遇到异常处理，如果只有jsp请求能捕获到异常，是不足够的， 有时候AJAX返回json数据时遇到异常。这时候默认的处理方式不能满足了， 需要自定义的方式支持同步和ajax异步异常处理。

或许大家都知道spring3的异常处理方法有：

1 以配置文件的方式进行异常管理

在配置dispacher-servlet.xml

<bean id="exceptionResolver" class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">

    <property name="defaultErrorView">
      <value>jsonView</value>
    </property>
   <property name="exceptionMappings">
      <props>
    <prop key="java.lang.Exception">/common/error.jsp</prop>   
      </props> 
    </property>
  </bean>

配置多个异常处理的地方

2以注解的方式配置异常管理

为了方便阅读， 把代码的地方发全一点

@Controller
public class ExceptionHandlerController
{
    private final Logger log = LoggerFactory.getLogger(getClass());
    
    @ExceptionHandler(ManagerSecurityException.class)
    public ModelAndView handleManagerSecurityException(ManagerSecurityException e,
            HttpServletResponse response)
    throws IOException
    {
        log.info("Manager exception handler " + e.getMessage());
        
        response.sendError(HttpServletResponse.SC_FORBIDDEN,
            e.getMessage());
         return new ModelAndView("viewName",new HashMap());
    }
}

这样的配置处理jstl请求jsp没有问题，

如果是jquery的 $.post的方法请求， 那么如果还是返回 error.jsp ， 那在 js的success函数里则不能很好地输出显示了。

问题又来了： 如果在 handleManagerSecurityException方法的上面打上注解 @ResponeBody

那么这样又只能返回 json格式串的异常处理， 你想同步请求跳到到error.jsp又不行啦！

解决办法是这样的：定制化异常处理

	<bean id="exceptionResolver" class="com.wsd.core.web.servlet.handle.CustomSimpleMappingExceptionResolver">
  		<property name="defaultErrorView">
   			<value>/common/error.jsp</value>
  		</property>
	 	<property name="exceptionMappings">
	   		<props>
				<prop key="java.lang.Exception">/common/error.jsp</prop>   
	   		</props> 
	  	</property>
 	</bean>

下面我们来看看CustomSimpleMappingExceptionResolver.java是如何做到支持JSP和JSON格式返回的异常错误的

	@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) {//JSP格式返回
			if(!(request.getHeader("accept").indexOf("application/json")>-1 || request.getHeader("X-Requested-With").indexOf("XMLHttpRequest")>-1)){//如果不是异步请求
				// 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{//JSON格式返回
				Map<String, Object> model=new HashMap<String, Object>();
				if(this.logger.isDebugEnabled()){
					model.put("debug", true); 
				}//exception
				model.put(ConfigConstants.RESULT, ex.getMessage());
				model.put("failure", true);
				try {
					response.getWriter().write("有异常啦!");
				} catch (IOException e) {
					e.printStackTrace();
				}
				return new ModelAndView();
			}
			return null;
		}
		else {
			return null;
		}
	}

这里判断了request.getHeader("accept").indexOf("application/json")是不是异步请求

下面给出同步和异步请求的Header

同步的text/html

=== MimeHeaders ===
host = localhost:8888
user-agent = Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.8) Gecko/20100722 Firefox/3.6.8
accept = text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
accept-language = en,zh;q=0.7,en-gb;q=0.3
accept-encoding = gzip,deflate
accept-charset = ISO-8859-1,utf-8;q=0.7,*;q=0.7
keep-alive = 115
connection = keep-alive
cookie = JSESSIONID=BB7441E4B481FF64A5BCC8E6F596C330

异步的application/json
=== MimeHeaders ===
host = localhost:8888
user-agent = Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.8) Gecko/20100722 Firefox/3.6.8
accept = application/json, text/javascript, */*
accept-language = en,zh;q=0.7,en-gb;q=0.3
accept-encoding = gzip,deflate
accept-charset = ISO-8859-1,utf-8;q=0.7,*;q=0.7
keep-alive = 115
connection = keep-alive
content-type = application/x-www-form-urlencoded
x-requested-with = XMLHttpRequest
referer = http://localhost:8888/auth/auth/dictionary/dictionaryForm.html
cookie = JSESSIONID=A4B59EA87C9B83B71C0D455634746411

请注意

try {
response.getWriter().write("有异常啦!");
} catch (IOException e) {
e.printStackTrace();
}
return new ModelAndView();

关键就在最后这1句 return new ModelAndView();

为什么不写 return null; 或者 return new ModelAndView('jsonView', model); 呢？

因为spring3的源码里这样写着了

	protected ModelAndView processHandlerException(HttpServletRequest request,
			HttpServletResponse response,
			Object handler,
			Exception ex) throws Exception {

		// Check registerer 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;
			}
			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;
	}

注意看

if (exMv != null) {
if (exMv.isEmpty()) {
return null;
}

这句和最后一句： throw ex;

如果你写 respone.getWriter().write("有异常啦"); 你也要 new一个空的ModelAndView，

上面的代码表明， 如果你 return null; 它就跑出异常 throw ex; 如果没人接收， 则会调用你配置的默认异常处理器

或者中断不做任何输出。

好了， 这样可以同时支持同步和AJAX异步请求异常处理了。

下面附上截图， 以免误人子弟~