context.go
func (ctx *Context) Param(key string) string {
	return ctx.Params.ByName(key)
}
func (ctx *Context) Param(key string) string {
	return ctx.Params.ByName(key)
}
// Param returns the value of the URL param.
// It is a shortcut for c.Params.ByName(key)
//     router.GET("/user/:id", func(c *gin.Context) {
//         // a GET request to /user/john
//         id := c.Param("id") // id == "john"
//     })