JavaServer Pages, 3rd Edition

Including Images with JSP

Example 6-1 illustrates an important detail regarding JSP and images. A common question is “How do I use JSP to include a dynamic image in a page?” The short answer is: you don’t.

First of all, a response can only contain one type of content^[1] so you can’t mix HTML and an image in the same response. You may recall from Chapter 2 that a browser handles an HTML response with <img> elements by sending a new request for each image and then merging the HTML and all images. So to include an image in a JSP-generated response, you do the same as you do in a regular HTML page; add an <img> element with the URI for the image. The only difference is that the URI may be decided at runtime, as in Examples Example 6-1 and Example 6-2.

Secondly, JSP is intended for text responses, not binary responses with image bytes. If you need to generate an image dynamically, you should use a servlet instead. In the JSP page, add the <img> element with a URI for the servlet and pass data it may need as request parameters in a query string:

<img src="imageGeneratorServlet?width=100&height=100">

^[1] This is true for the general case. An HTTP response can actually contain multiple parts of different types when special headers and delimiters are used, but generating such a response with JSP isn’t recommended.