java - Spring mvc 拦截器异常

Question

我的项目是基于spring mvc的，我写了一个拦截器来拦截请求，我想从请求中获取参数，下面是我的代码:

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    HandlerMethod maControl = (HandlerMethod) handler;  
    Method pmrResolver = (Method) maControl.getMethod();  
    String methodName = pmrResolver.getName(); 
        ....
}

但现在它抛出一个异常:

java.lang.ClassCastException: org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler cannot be cast to  org.springframework.web.method.HandlerMethod

异常的原因是什么？

Answer 1

这只是意味着 handler 不是 HandlerMethod 的实例，因此转换失败。类型转换前检查如下:

if (handler instanceof HandlerMethod) {
    HandlerMethod maControl = (HandlerMethod) handler;  
    Method pmrResolver = (Method) maControl.getMethod();  
    String methodName = pmrResolver.getName(); 
    // ...
}