四、SpringMVC异常处理

1. SpringMVC默认三个异常处理类

• ExceptionHandlerExceptionResolver：处理@ExceptionHandler注解
• ResponseStatusExceptionResolver：处理@ResponseStatus注解
• DefaultHandlerExceptionResolver：处理SpringMVC自带的异常

如果以上3个异常解析器都无法处理，会上抛给tomcat，处理异常内部的默认工作流程：所有异常解析器依次尝试解析，解析完成进行后续操作，解析失败，下一个解析器继续尝试解析。

2. @ExceptionHandler注解异常

@ExceptionHandler标注在方法上

• 方法上写一个Exception用来接收发生的异常。
• 要携带异常信息不能给参数位置写Model，正确的做法是返回ModelAndView。
• 如果有多个@ExceptionHandler都能处理这个异常，精确优先。

@ExceptionHandler(value = { ArithmeticException.class, NullPointerException.class }) 
// 告诉SpringMVC,这个方法专门处理这个类发送的所有异常
public ModelAndView handleException01(Exception exception) {
    System.out.println("handleException01..." + exception);
    ModelAndView view = new ModelAndView("myerror");
    view.addObject("ex", exception);    
    return view;
}

@ExceptionHandler统一异常处理

• 将@ExceptionHandler放在一个单独的类中，进行全局异常处理
• 统一异常管理类需要通过@ControllerAdvice注解加入IoC容器中
• 全局异常处理与本类异常处理同时存在，本类优先

@ControllerAdvice
public class MyException {
    // 处理空指针异常
    @ExceptionHandler(value = { NullPointerException.class })
    public ModelAndView handleException01(Exception exception) {
        System.out.println("全局的handleException01..." + exception);
        ModelAndView view = new ModelAndView("myerror");
        view.addObject("ex", exception);
        return view;
    }

    // 处理算数异常
    @ExceptionHandler(value = { ArithmeticException.class })
    public ModelAndView handleException02(Exception exception) {
        System.out.println("全局的handleException02..." + exception);
        ModelAndView view = new ModelAndView("myerror");
        view.addObject("ex", exception);
        return view;
    }
}

3. @ResponseStatus注解异常
@ResponseStatus注解标注在自定义异常上，用于设置自定义异常信息

@ResponseStatus(reason = "用户被拒绝登录", value = HttpStatus.NOT_ACCEPTABLE)
public class UsernameNotFoundException extends RuntimeException {
    private static final long serialVersionUID = 1L;
}

3. DefaultHandlerExceptionResolver默认异常
DefaultHandlerExceptionResolver包含以下默认异常

源码:
public class DefaultHandlerExceptionResolver extends AbstractHandlerExceptionResolver {
    ...
    @Override
    protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response,
            Object handler, Exception ex) {

        try {
            if (ex instanceof NoSuchRequestHandlingMethodException) {
                return handleNoSuchRequestHandlingMethod((NoSuchRequestHandlingMethodException) ex, request, response,
                        handler);
            }
            else if (ex instanceof HttpRequestMethodNotSupportedException) {
                return handleHttpRequestMethodNotSupported((HttpRequestMethodNotSupportedException) ex, request,
                        response, handler);
            }
            else if (ex instanceof HttpMediaTypeNotSupportedException) {
                return handleHttpMediaTypeNotSupported((HttpMediaTypeNotSupportedException) ex, request, response,
                        handler);
            }
            else if (ex instanceof HttpMediaTypeNotAcceptableException) {
                return handleHttpMediaTypeNotAcceptable((HttpMediaTypeNotAcceptableException) ex, request, response,
                        handler);
            }
            else if (ex instanceof MissingPathVariableException) {
                return handleMissingPathVariable((MissingPathVariableException) ex, request,
                        response, handler);
            }
            else if (ex instanceof MissingServletRequestParameterException) {
                return handleMissingServletRequestParameter((MissingServletRequestParameterException) ex, request,
                        response, handler);
            }
            else if (ex instanceof ServletRequestBindingException) {
                return handleServletRequestBindingException((ServletRequestBindingException) ex, request, response,
                        handler);
            }
            else if (ex instanceof ConversionNotSupportedException) {
                return handleConversionNotSupported((ConversionNotSupportedException) ex, request, response, handler);
            }
            else if (ex instanceof TypeMismatchException) {
                return handleTypeMismatch((TypeMismatchException) ex, request, response, handler);
            }
            else if (ex instanceof HttpMessageNotReadableException) {
                return handleHttpMessageNotReadable((HttpMessageNotReadableException) ex, request, response, handler);
            }
            else if (ex instanceof HttpMessageNotWritableException) {
                return handleHttpMessageNotWritable((HttpMessageNotWritableException) ex, request, response, handler);
            }
            else if (ex instanceof MethodArgumentNotValidException) {
                return handleMethodArgumentNotValidException((MethodArgumentNotValidException) ex, request, response,
                        handler);
            }
            else if (ex instanceof MissingServletRequestPartException) {
                return handleMissingServletRequestPartException((MissingServletRequestPartException) ex, request,
                        response, handler);
            }
            else if (ex instanceof BindException) {
                return handleBindException((BindException) ex, request, response, handler);
            }
            else if (ex instanceof NoHandlerFoundException) {
                return handleNoHandlerFoundException((NoHandlerFoundException) ex, request, response, handler);
            }
        }
        catch (Exception handlerException) {
            if (logger.isWarnEnabled()) {
                logger.warn("Handling of [" + ex.getClass().getName() + "] resulted in Exception", handlerException);
            }
        }
        return null;
    }
    ...
}

如下HttpRequestMethodNotSupportedException请求方式不对。使用GET对POST方法进行访问

@RequestMapping(value = "/handle03", method = RequestMethod.POST)
public String postMethod() {
    return "success";
}

4. 没有找到对应异常处理类
若没有对应异常处理类，会进入对应服务器错误页面