.异常分为:预期异常、运行时异常
dao、service、controller三层中有异常,依次向上抛出直到SpringMVC处理。
而SpringMVC交给HandlerExceptionResolver(异常处理器)
程序员则需要实现这个类
示例:
package org.dreamtech.springmvc.exception;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.springframework.web.servlet.HandlerExceptionResolver;import org.springframework.web.servlet.ModelAndView;/** * * @author YiQing * * 异常处理器自定义实现类 */public class CustomExceptionResolver implements HandlerExceptionResolver { @Override public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object obj, Exception e) { /* * request 请求 response 响应 * obj 字符串,发生异常的地方(包名.类名.方法名) * e 异常 */ ModelAndView mav = new ModelAndView(); mav.addObject("error","异常"); mav.setViewName("error"); return mav; }}
使用前记得配给SpringMVC:
解释:如果程序中出现了异常,就会执行这个方法,并且返回error视图
使用场景:开发网站时候,用户由于不当操作使程序异常,会看到Tomcat报错,这大大影响用户体验,可以统一设置一个错误页面,友好提示。
上边这种方式异常不在意料之中,而如果我们需要主动抛出异常的话(预期异常):
使用场景:用户注册时候,用户名密码不能为空(如果不采取前端校验),这时候可以在后端主动抛出异常,并返回对应提示信息。
首先自定义异常:
package org.dreamtech.springmvc.exception;/** * 自定义异常 * @author YiQing * */public class MessageException extends Exception { private String msg; public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } public MessageException(String msg) { super(); this.msg = msg; }}
主动触发异常:
if(username==""){ throw new MessageException("用户名不为空"); }
这时候异常处理器就可以修改成完整版:
package org.dreamtech.springmvc.exception;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.springframework.web.servlet.HandlerExceptionResolver;import org.springframework.web.servlet.ModelAndView;/** * * @author YiQing * */public class CustomExceptionResolver implements HandlerExceptionResolver { @Override public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object obj, Exception e) { ModelAndView mav = new ModelAndView(); if (e instanceof MessageException) { MessageException me = (MessageException) e; mav.addObject("error", me.getMsg()); mav.setViewName("login"); } else { mav.addObject("error", "未知异常"); mav.setViewName("error"); } return mav; }}