HandlerInterceptor中的preHandle的参数handler怎么获取到目标方法并做入参的赋值

可以通过HandlerExecutionChain对象获取目标方法的信息，然后使用反射机制对目标方法的入参进行赋值。具体实现可以参考以下代码：

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    if (handler instanceof HandlerMethod) {
        HandlerMethod handlerMethod = (HandlerMethod) handler;
        Method method = handlerMethod.getMethod();
        Object[] args = new Object[method.getParameterTypes().length];
        Annotation[][] parameterAnnotations = method.getParameterAnnotations();
        for (int i = 0; i < parameterAnnotations.length; i++) {
            for (Annotation annotation : parameterAnnotations[i]) {
                if (annotation.annotationType().equals(RequestBody.class)) {
                    args[i] = readRequestBody(request, method.getParameterTypes()[i]);
                    break;
                } else if (annotation.annotationType().equals(RequestParam.class)) {
                    args[i] = readRequestParam(request, method.getParameterTypes()[i], method.getParameters()[i].getName());
                    break;
                } else if (annotation.annotationType().equals(RequestHeader.class)) {
                    args[i] = readRequestHeader(request, method.getParameterTypes()[i], method.getParameters()[i].getName());
                    break;
                } else if (annotation.annotationType().equals(PathVariable.class)) {
                    args[i] = readPathVariable(request, method.getParameterTypes()[i], ((PathVariable) annotation).value());
                    break;
                }
            }
        }
        request.setAttribute("args", args);
    }
    return true;
}

private Object readRequestBody(HttpServletRequest request, Class<?> clazz) throws IOException {
    String body = IOUtils.toString(request.getReader());
    return objectMapper.readValue(body, clazz);
}

private Object readRequestParam(HttpServletRequest request, Class<?> clazz, String paramName) {
    String value = request.getParameter(paramName);
    return conversionService.convert(value, clazz);
}

private Object readRequestHeader(HttpServletRequest request, Class<?> clazz, String headerName) {
    String value = request.getHeader(headerName);
    return conversionService.convert(value, clazz);
}

private Object readPathVariable(HttpServletRequest request, Class<?> clazz, String variableName) {
    String value = (String) request.getAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE).get(variableName);
    return conversionService.convert(value, clazz);
}