c# 图片上传和显示的实现方法

1.界面代码

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="UploadPic.aspx.cs" Inherits="Pic_Try.UploadPic" %>





  
  


  

  

  

  
上传图片格式为.jpg, .gif, .bmp,.png,图片大小不得超过8M
  

  
 

2.后台代码UploadPic.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using System.Security.Cryptography;
using System.Web.Security;

namespace Pic_Try
{
  public partial class UploadPic : System.Web.UI.Page
  {
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void btn_upload_Click(object sender, EventArgs e)
    {
      Boolean fileOk = false;
      if (pic_upload.HasFile)//验证是否包含文件
      {
        //取得文件的扩展名,并转换成小写
        string fileExtension = Path.GetExtension(pic_upload.FileName).ToLower();
        //验证上传文件是否图片格式
        fileOk = IsImage(fileExtension);

        if (fileOk)
        {
          //对上传文件的大小进行检测，限定文件最大不超过8M
          if (pic_upload.PostedFile.ContentLength < 8192000)
          {
            string filepath = "/images/";
            if (Directory.Exists(Server.MapPath(filepath)) == false)//如果不存在就创建file文件夹
            {
              Directory.CreateDirectory(Server.MapPath(filepath));
            }
            string virpath = filepath + CreatePasswordHash(pic_upload.FileName, 4) + fileExtension;//这是存到服务器上的虚拟路径
            string mappath = Server.MapPath(virpath);//转换成服务器上的物理路径
            pic_upload.PostedFile.SaveAs(mappath);//保存图片
            //显示图片
            pic.ImageUrl = virpath;
            //清空提示
            lbl_pic.Text = "";
          }
          else {
            pic.ImageUrl = "";
            lbl_pic.Text = "文件大小超出8M！请重新选择！";
          }
        }
        else {
          pic.ImageUrl = "";
          lbl_pic.Text = "要上传的文件类型不对！请重新选择！";
        }
      }
      else
      {
        pic.ImageUrl = "";
        lbl_pic.Text = "请选择要上传的图片！";
      }
    }

    /// 

    /// 验证是否指定的图片格式
    /// 
    /// 
    /// 
    public bool IsImage(string str) {
      bool isimage = false;
      string thestr = str.ToLower();
      //限定只能上传jpg和gif图片
      string[] allowExtension = { ".jpg", ".gif", ".bmp",".png" };
      //对上传的文件的类型进行一个个匹对
      for (int i = 0; i < allowExtension.Length; i++)
      {
        if (thestr == allowExtension[i])
        {
          isimage = true;
          break;
        }
      }
      return isimage;
    }

    /// 

    /// 创建一个指定长度的随机salt值
    /// 
    public string CreateSalt(int saltLenght)
    {
      //生成一个加密的随机数
      RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
      byte[] buff = new byte[saltLenght];
      rng.GetBytes(buff);
      //返回一个Base64随机数的字符串
      return Convert.ToBase64String(buff);
    }

    
    /// 

    /// 返回加密后的字符串
    /// 
    public string CreatePasswordHash(string pwd, int saltLenght)
    {
      string strSalt = CreateSalt(saltLenght);
      //把密码和Salt连起来
      string saltAndPwd = String.Concat(pwd, strSalt);
      //对密码进行哈希
      string hashenPwd = FormsAuthentication.HashPasswordForStoringInConfigFile(saltAndPwd, "sha1");
      //转为小写字符并截取前16个字符串
      hashenPwd = hashenPwd.ToLower().Substring(0, 16);
      //返回哈希后的值
      return hashenPwd;
    }
  }
}

3.最后防止上传大文件图片时报错，配置文件添加配置Web.config