springmvc-异常处理器以及拦截器

异常处理器

springmvc异常处理

dao、service、controller都可能出现异常，当出现异常都通过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，SpringMVC提供全局异常处理器（一个系统只有一个异常处理器）进行统一异常处理。

自定义异常类

public class MyException extends Exception {

    private String message;

    public MyException(String message) {
        this.message = message;
    }

    @Override
    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

编写异常处理器
springmvc的异常处理器需要实现HandlerExceptionResolver 接口

public class MyExceptionResolver implements HandlerExceptionResolver {

    /**
     * 处理异常
     * @param request
     * @param response
     * @param handler
     * @param ex 抛出的异常
     * @return
     */
    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        //获取异常对象
        MyException myException = null;
        //如果是预期的异常，则获取异常信息
        if(ex instanceof MyException){
            myException = (MyException) ex;
        }else {
        //不是预测的异常，则统一为系统维护....
            myException = new MyException("系统正在维护...");
        }
        //创建ModelAndView对象
        ModelAndView modelAndView = new ModelAndView();
        modelAndView.addObject("error",myException.getMessage() );
        //返回错误提示页面
        modelAndView.setViewName("error");
        return modelAndView;
    }
}

配置异常处理器

    
    <bean id="myException" class="com.lb.exception.MyExceptionResolver"/>

 @RequestMapping("/exception")
    public String testException() throws Exception {
        System.out.println("testException执行了...");
        //模拟异常
        int i = 1/0;
        return "success";
    }

 @RequestMapping("/exception")
    public String testException() throws MyException {
        System.out.println("testException执行了...");
        //模拟异常
        try {
            int i = 1/0;
        } catch (Exception e) {
            e.printStackTrace();
            throw new MyException("出错啦...");
        }
        return "success";
    }

拦截器

Springmvc的处理器拦截器类似于Servlet 开发中的过滤器Filter，用于对处理器进行预处理和后处理。

springmvc的自定义拦截器需要实现HandlerInterceptor 接口，该接口有三个方法，preHandle： 进入controller方法之前执行，postHandle： 进入controller方法之后，返回ModekAndView之前执行，以及afterCompletion： 执行完controller方法之后执行

public class MyInterceptor implements HandlerInterceptor {

    /**
     * controller处理前执行
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("拦截器执行了...");
        return true;
    }


    /**
     * controller处理后执行
     * @param request
     * @param response
     * @param handler
     * @param modelAndView
     * @throws Exception
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }
}

配置拦截器

    
    <mvc:interceptors>
        
        <mvc:interceptor>
            
            <mvc:mapping path="/**"/>
            
            
            
            <bean class="com.lb.interceptor.MyInterceptor"/>
        mvc:interceptor>
    mvc:interceptors>