请问在gin中为什么要自己建立一个结构体来获取response

请问在本节课中，为什么要自己建立一个responseBodyWriter结构体来获取response？

type responseBodyWriter struct {
    gin.ResponseWriter
    body *bytes.Buffer
}

func (r responseBodyWriter) Write(b []byte) (int, error) {
    r.body.Write(b)
    return r.ResponseWriter.Write(b)
}

// Logger 记录请求日志
func Logger() gin.HandlerFunc {
    return func(c *gin.Context) {

        // 获取 response 内容
        w := &responseBodyWriter{body: &bytes.Buffer{}, ResponseWriter: c.Writer}
        c.Writer = w

        //.....
    ｝
｝