swag init can't generate api info in swagger.json

[gjxgjxgjxgjx]

when i run 'swag init', no api info has been generated in swagger.json

swag.exe version v1.16.3
go version go1.22.1 windows/amd64
i use the examples provided on the official website and filled in the correct package name.

package main

import (
	"net/http"

	docs "oj/docs"

	"github.com/gin-gonic/gin"
	swaggerfiles "github.com/swaggo/files"
	ginSwagger "github.com/swaggo/gin-swagger"
)

// @BasePath /api/v1

// PingExample godoc
// @Summary ping example
// @Schemes
// @Description do ping
// @Tags example
// @Accept json
// @Produce json
// @Success 200 {string} Helloworld
// @Router /example/helloworld [get]
func Helloworld(g *gin.Context) {
	g.JSON(http.StatusOK, "helloworld")
}

func main() {
	r := gin.Default()
	docs.SwaggerInfo.BasePath = "/api/v1"
	v1 := r.Group("/api/v1")
	{
		eg := v1.Group("/example")
		{
			eg.GET("/helloworld", Helloworld)
		}
	}
	r.GET("/swagger/*any", ginSwagger.WrapHandler(swaggerfiles.Handler))
	r.Run(":8080")

}