SpringMVC中的异常处理

　　springmvc在处理请求过程中出现异常信息交由异常处理器进行处理，自定义异常处理器可以实现一个系统的异常处理逻辑。

1. 异常处理思路

　　系统中异常包括两类：预期异常和运行时异常RuntimeException，前者通过捕获异常从而获取异常信息，后者主要通过规范代码开发、测试通过手段减少运行时异常的发生。

　　系统的dao、service、controller出现都通过throws Exception向上抛出，最后由springmvc前端控制器交由异常处理器进行异常处理，如下图：

2. 自定义异常

　　为了区别不同的异常通常根据异常类型自定义异常类，这里我们创建一个自定义系统异常，如果controller、service、dao抛出此类异常说明是系统预期处理的异常信息。(自定义异常继承Exception类)

package cn.rodge.ssm.exception;

public class CustomerException extends Exception {
   private static final long serialVersionUID = -3387516993124229948L;
   private String expMessage;
   public String getExpMessage() {
       return expMessage;
   }
   public void setExpMessage(String expMessage) {
       this.expMessage = expMessage;
   }

   public CustomerException(String expMessage) {
       super();
       this.expMessage = expMessage;
   }
   public CustomerException() {
       super();
   }
   public CustomerException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
       super(message, cause, enableSuppression, writableStackTrace);
   }
   public CustomerException(String message, Throwable cause) {
       super(message, cause);
   }
   public CustomerException(Throwable cause) {
       super(cause);
   }

}

3. 自定义异常处理器

　　自定义异常处理器实现HandlerExceptionResolver接口

package cn.rodge.ssm.exception;

import java.io.PrintWriter;
import java.io.StringWriter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.ModelAndView;

public class GolbalException implements HandlerExceptionResolver {

   @Override
   public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler,
           Exception exception) {
       exception.printStackTrace();
       String msg = null;
       ModelAndView modelAndView = new ModelAndView();
       //1.判断异常种类
       if (exception instanceof CustomerException) {
           //2.如果是自定义异常,异常强制转换,并获取异常信息
           CustomerException customerException = (CustomerException) exception;
           msg = customerException.getExpMessage();
       } else {
           //3.如果是runtimeexception子类,获取异常信息
           StringWriter stringWriter = new StringWriter();
           PrintWriter printWriter = new PrintWriter(stringWriter);
           exception.printStackTrace(printWriter);
           msg = stringWriter.toString();
       }
       modelAndView.addObject("msg", msg);
       modelAndView.setViewName("error");
       return modelAndView;
   }
}

4. 配置错误页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
   <h1>错误友好页面</h1>
   <br>
   <h2>异常信息:</h2>
   <br>
   ${msg}
</body>
</html>

5. 异常处理器配置

在springmvc.xml中配置异常处理器

<bean class="cn.rodge.ssm.exception.GolbalException"></bean>

6. 异常测试

@RequestMapping("/itemList.action")
   public String itemList (Model model) throws CustomerException {

       //异常测试
        if (true) {
//           throw new CustomerException("我是自定义异常~~~~~~~~");
           throw new RuntimeException("系统异常");
       }

       //调用业务层查询订单数据
       List<Items> itemList = itemService.findAll();
       //将查询结果保存在model中
       model.addAttribute("itemList", itemList);
       //页面转发
       return "itemList";
   }