上传图片+生成缩略图 ashx代码

html页面

<form action="Handlers/UploadImageHandler.ashx" method="post" enctype="multipart/form-data">
<input type="file" name="image"/>
<input type="hidden" value="web" name="directory" />
<input type="submit" name="submitbtn" />
</form>

//一般处理程序

public class PicUploadHander : IHttpHandler
{

public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/plain";
//验证上传的权限TODO
string _fileNamePath = "";
try
{
_fileNamePath = context.Request.Files[0].FileName;
//开始上传
string _savedFileResult = UpLoadImage(_fileNamePath, context);
context.Response.Write(_savedFileResult);
}
catch
{
context.Response.Write("上传提交出错");
}
}

public string UpLoadImage(string fileNamePath, HttpContext context)
{
try
{
string serverPath = System.Web.HttpContext.Current.Server.MapPath("~");

string toFilePath = Path.Combine(serverPath, @"Content\Upload\Images\");

//获取要保存的文件信息
FileInfo file = new FileInfo(fileNamePath);
//获得文件扩展名
string fileNameExt = file.Extension;

//验证合法的文件
if (CheckImageExt(fileNameExt))
{
//生成将要保存的随机文件名
string fileName = GetImageName() + fileNameExt;

//获得要保存的文件路径
string serverFileName = toFilePath + fileName;
//物理完整路径
string toFileFullPath = serverFileName; //HttpContext.Current.Server.MapPath(toFilePath);

//将要保存的完整文件名
string toFile = toFileFullPath;//+ fileName;

///创建WebClient实例
WebClient myWebClient = new WebClient();
//设定windows网络安全认证 方法1
myWebClient.Credentials = CredentialCache.DefaultCredentials;
////设定windows网络安全认证 方法2
context.Request.Files[0].SaveAs(toFile);

//上传成功后网站内源图片相对路径
string relativePath = System.Web.HttpContext.Current.Request.ApplicationPath
+ string.Format(@"Content/Upload/Images/{0}", fileName);

/*
比例处理
微缩图高度（DefaultHeight属性值为 400）
*/
System.Drawing.Image img = System.Drawing.Image.FromFile(toFile);
int width = img.Width;
int height = img.Height;
float ratio = (float)width / height;

//微缩图高度和宽度
int newHeight = height <= DefaultHeight ? height : DefaultHeight;
int newWidth = height <= DefaultHeight ? width : Convert.ToInt32(DefaultHeight * ratio);

FileInfo generatedfile = new FileInfo(toFile);
string newFileName = "Thumb_" + generatedfile.Name;
string newFilePath = Path.Combine(generatedfile.DirectoryName, newFileName);

PictureHandler.CreateThumbnailPicture(toFile, newFilePath, newWidth, newHeight);

string thumbRelativePath = System.Web.HttpContext.Current.Request.ApplicationPath
+ string.Format(@"/Content/Upload/Images/{0}", newFileName);

//返回原图和微缩图的网站相对路径
relativePath = string.Format("{0},{1}", relativePath, thumbRelativePath);

return relativePath;
}
else
{
return "文件格式非法，请上传gif或jpg格式的文件。";
//throw new Exception("文件格式非法，请上传gif或jpg格式的文件。");
}
}
catch (Exception ex)
{
return ex.Message;
}
}

public bool IsReusable
{
get
{
return false;
}
}

#region Private Methods
/// <summary>
/// 检查是否为合法的上传图片
/// </summary>
/// <param name="_fileExt"></param>
/// <returns></returns>
private bool CheckImageExt(string imageExt)
{
string[] allowExt = new string[] { ".gif", ".jpg", ".jpeg", ".bmp" };
//for (int i = 0; i < allowExt.Length; i++)
//{
// if (allowExt[i] == _ImageExt) { return true; }
//}

StringComparer stringComparer = StringComparer.OrdinalIgnoreCase;

return allowExt.Any(c => stringComparer.Equals(c, imageExt));

}

private string GetImageName()
{
Random rd = new Random();
StringBuilder serial = new StringBuilder();
serial.Append(DateTime.Now.ToString("yyyyMMddHHmmssff"));
serial.Append(rd.Next(0, 999999).ToString());
return serial.ToString();

}

public int DefaultHeight
{
get
{
//此处硬编码了，可以写入配置文件中。
return 100;
}
}

#endregion
}

//缩略图处理相关类

public static class PictureHandler
{
/// <summary>
/// 图片微缩图处理
/// </summary>
/// <param name="srcPath">源图片</param>
/// <param name="destPath">目标图片</param>
/// <param name="width">宽度</param>
/// <param name="height">高度</param>
public static void CreateThumbnailPicture(string srcPath, string destPath, int width, int height)
{
//根据图片的磁盘绝对路径获取 源图片 的Image对象
System.Drawing.Image img = System.Drawing.Image.FromFile(srcPath);

//bmp： 最终要建立的 微缩图 位图对象。
Bitmap bmp = new Bitmap(width, height);

//g: 绘制 bmp Graphics 对象
Graphics g = Graphics.FromImage(bmp);
g.Clear(Color.Transparent);
//为Graphics g 对象 初始化必要参数，很容易理解。
g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

//源图片宽和高
int imgWidth = img.Width;
int imgHeight = img.Height;

//绘制微缩图
g.DrawImage(img, new System.Drawing.Rectangle(0, 0, width, height), new System.Drawing.Rectangle(0, 0, imgWidth, imgHeight)
, GraphicsUnit.Pixel);

ImageFormat format = img.RawFormat;
ImageCodecInfo info = ImageCodecInfo.GetImageEncoders().SingleOrDefault(i => i.FormatID == format.Guid);
EncoderParameter param = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);
EncoderParameters parameters = new EncoderParameters(1);
parameters.Param[0] = param;
img.Dispose();

//保存已生成微缩图，这里将GIF格式转化成png格式。
if (format == ImageFormat.Gif)
{
destPath = destPath.ToLower().Replace(".gif", ".png");
bmp.Save(destPath, ImageFormat.Png);
}
else
{
if (info != null)
{
bmp.Save(destPath, info, parameters);
}
else
{

bmp.Save(destPath, format);
}
}

img.Dispose();
g.Dispose();
bmp.Dispose();
}
}