使用@ControllerAdvice + @ExceptionHandler建立全局异常拦截

1. @ControllerAdvice 注解定义全局异常处理类

   @ControllerAdvice
   public class GlobalExceptionHandler {
   }
   

2. @ExceptionHandler 注解声明异常处理方法

   @ControllerAdvice
   public class GlobalExceptionHandler{
       @ExceptionHandler(Exception.class)
       @ResponseBody
       public String handleException() {
           ex.printStackTrace(); 
           return "fail";
       }
   }
   

   方法handleException()会处理所有Controller层抛出的Exception及其子类的异常，Controller层就不需要单独处理异常了。
   但如上代码只能处理 Controller 层的异常，对于未进入Controller的异常，如Interceptor（拦截器）层的异常，Spring 框架层的异常无效，还是会将错误直接返回给用户。对此，只需要在配置文件中添加：

   spring.mvc.throw-exception-if-no-handler-found=true
   spring.resources.add-mappings=false
   

3. 被 @ExceptionHandler 注解的方法还可以声明很多种参数类型，具体可以参考文档：https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/bind/annotation/ExceptionHandler.html
   这里我选择了httpServletRequest, HttpServletResponse httpServletResponse, Exception ex三个参数，应用如下：

   @ControllerAdvice
   public class GlobalExceptionHandler{
       @ExceptionHandler(Exception.class)
       @ResponseBody
       public CommonReturnType handleException(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Exception ex) {
           ex.printStackTrace(); // 线上环境替换为对应的log
           Map<String,Object> responseData = new HashMap<>();
           if( ex instanceof BusinessException){
               BusinessException businessException = (BusinessException)ex;
               responseData.put("errCode",businessException.getErrCode());
               responseData.put("errMsg",businessException.getErrMsg());
           }else if(ex instanceof ServletRequestBindingException){
               responseData.put("errCode",BusinessError.UNKNOWN_ERROR.getErrCode());
               responseData.put("errMsg","url绑定路由问题");
           }else if(ex instanceof NoHandlerFoundException){
               responseData.put("errCode",BusinessError.UNKNOWN_ERROR.getErrCode());
               responseData.put("errMsg","没有找到对应的访问路径");
           }else{
               responseData.put("errCode", BusinessError.UNKNOWN_ERROR.getErrCode());
               responseData.put("errMsg", BusinessError.UNKNOWN_ERROR.getErrMsg());
           }
           return CommonReturnType.create(responseData,"fail");
       }
   }
   

如此，所有的 Controller 层的异常日志都可以通过GlobalExceptionHandler 记录。Controller 层也不需要在手动记录异常日志了。