asp.net core mvc 文件上传，下载，预览

//文件上传用到了IformFile接口
1.1文件上传视图

<form action="/stu/upload" method="post" enctype="multipart/form-data"><input type="file" name="img" /><input type="submit" value="上传" />
</form>

1.2文件上传后端代码

  private readonly IWebHostEnvironment _webHostEnvironment;public StuController(IWebHostEnvironment webHostEnvironment){//使用内置的服务读取项目路径_webHostEnvironment = webHostEnvironment;}public IActionResult upload(){return View();}[HttpPost]public IActionResult upload(IFormFile img){//返回根目录var contentpath = _webHostEnvironment.ContentRootPath;//项目跟目录下创建一个upload文件夹，存放上传的图片var filepath = Path.Combine(contentpath, "upload", img.FileName);//创建一个文件流using (FileStream fs = new FileStream(filepath, FileMode.Create, FileAccess.Write))//把上传的文件写入文件中img.CopyTo(fs);return Content("上传成功");}

1.3 运行效果
在这里插入图片描述
2.1下载文件视图

@Html.ActionLink("下载","downloadImg")

2.2后端代码（我这写死了，实际项目是前端传参下载图片的参数到后端）

 public byte[] GetImageBytes(){var rootpath = _webHostEnvironment.ContentRootPath;var filepath = Path.Combine(rootpath, "upload", "冒泡排序.png");string imagePath = filepath;byte[] imageBytes;try{using (FileStream fs = new FileStream(imagePath, FileMode.Open, FileAccess.Read)){using (BinaryReader br = new BinaryReader(fs)){imageBytes = br.ReadBytes((int)fs.Length);}}}catch (Exception ex){// 处理异常Console.WriteLine("读取图片文件时出错：" + ex.Message);imageBytes = null;}return imageBytes;}public IActionResult downloadImg(){byte[] imageBytes = GetImageBytes(); // 从某处获取图片的字节数组string fileName = "image.jpg";return File(imageBytes, "image/png", fileName);}

3.1预览图片视图

<img src="@Url.Action("GetImage", "stu", new { imageName = "4.jpg" })" alt="Image Preview">
<style>img{width:300px;height:400px;}
</style>

3.2后端代码

 public IActionResult GetImage(string imageName){var rootpath = _webHostEnvironment.ContentRootPath;var imagePath = Path.Combine(rootpath, "upload", imageName);var imageBytes = System.IO.File.ReadAllBytes(imagePath);return File(imageBytes, "image/jpeg");}