Michael Teper

Example – An ASP.NET handler that returns a dynamically generated image

This is a verbatim excerpt from a Microsoft employee post on changes in ASP.NET 2.0 from Beta 1 to Beta 2:

<%@ webhandler="" language="C#" class="ImageHandler" %="">


using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Web;
using System.Web.Caching;


public class ImageHandler : IHttpHandler {


 public void ProcessRequest (HttpContext context) {


 // Get the image ID from querystring, and use it to generate a cache key.
 String imageID = context.Request.QueryString["PhotoID"];
 String cacheKey = context.Request.CurrentExecutionFilePath + ":" + imageID;


 Byte[] imageBytes;


 // Check if the cache contains the image.
 Object cachedImageBytes = context.Cache.Get(cacheKey);


 if (cachedImageBytes != null)
 {
 imageBytes = (Byte[])cachedImageBytes;
 }
 else
 {
 // Get image from business layer, and save it into a Byte array as JPEG.
 Image im = PhotoLibrary.GetImage("PhotoID");


 MemoryStream stream = new MemoryStream();


 im.Save(stream, ImageFormat.Jpeg);
 stream.Close();
 im.Dispose();
 imageBytes = stream.GetBuffer();

 // Store it in the cache (to be expired after 2 hours).
 context.Cache.Add(cacheKey, imageBytes, null, 
 DateTime.MaxValue, new TimeSpan(2, 0, 0), 
 CacheItemPriority.Normal, null);
 }


 // Send back image.
 context.Response.ContentType = "image/jpeg";
 context.Response.Cache.SetCacheability(HttpCacheability.Public);
 context.Response.BufferOutput = false;
 context.Response.OutputStream.Write(imageBytes, 0, imageBytes.Length);
 }


 public bool IsReusable {

 get {


 return false;


 }
 }
}



Thanks, 



Shanku Niyogi 
Group Program Manager 
Web Platform and Tools Team

posted @ Tuesday, August 17, 2004 9:34 AM