JSP skills: Send dynamic images

Have you ever thought about sending dynamic images from JSP pages (or Servlets? This tip tells you how to do it. To run the code here, you need a tomcat or other web server that supports JSP 1.1.

When a Web page is sent with the MIME type of image/JPEG (or other image formats), your browser treats the returned result as an image and then displays the image, as part of a page or as an image itself. To set the MIME type for your JSP page, you need to set the contenttype attribute of the page:

<% @ Page contenttype = "image/JPEG"... %> Then you need to create a bufferedimage to draw your dynamic image: Bufferedimage image = new bufferedimage (width, Height, bufferedimage. type_int_rgb );

After creating a bufferedimage, You need to obtain the graphic environment for drawing, a graphics or graphics2d object:

Graphics G = image. getgraphics (); // Or Graphics2d g2d = image. creategraphics ();

From now on, you can draw the image content. The image environment will be painted to bufferedimage. This image is black at first, so it is a good idea to fill the image with the background color you want. Then, when you complete the image painting, you need to dispose the graphic environment:

G. Dispose (); // Or G2d. Dispose ();

Once the image is drawn, you return the image in response. You can use the custom imageencoder class in the non-standard com.sun.image.codec.jpeg package to encode the image, or if you use jdk1.4, you can use the standard ImageIO class. There is a trick when using tranquility imageencoder. You must obtain servletoutputstream from servletresponse, instead of using the implied JSP output variable out.

Servletoutputstream SOS = response. getoutputstream (); Required imageencoder encoder = Required codec. createjpegencoder (SOS ); Encoder. encode (image ); // Or ImageIO. Write (image, "Jpeg", out );

Here there is a scheme from all possibilities (such as G. dispose (); or g2d. dispose ();) selects a complete example. in this example, a random polygon is drawn using a graphics object, and the image is drawn using jpegimageencoder. You can freely set the number of vertices of a polygon to get a more complex shape. In other words, there are more vertices and edges.

To run this example, place the JSP code from "<% @" to the last "%>" into an image. in the JSP file, place the file to a location that can be found on your Web server. When Tomcat is used, it is the root directory. start Tomcat and access http: // localhost: 8080/image. JSP.

<% @ Page contenttype = "image/JPEG" Import = "Java. AWT. *, java. AWT. image .*, Com.sun.image.codec.jpeg. *, java. util .*" %> <% // Create Image Int width = 200, Height = 200; Bufferedimage image = new bufferedimage (width, Height, bufferedimage. type_int_rgb ); // Get drawing Context Graphics G = image. getgraphics (); // Fill background G. setcolor (color. White ); G. fillrect (0, 0, width, height ); // Create Random Polygon Polygon poly = new polygon (); Random random = new random (); For (INT I = 0; I <5; I ++ ){ Poly. addpoint (random. nextint (width ), Random. nextint (height )); } // Fill Polygon G. setcolor (color. Cyan ); G. fillpolygon (poly ); // Dispose Context G. Dispose (); // Send back Image Servletoutputstream SOS = response. getoutputstream (); Required imageencoder encoder = Required codec. createjpegencoder (SOS ); Encoder. encode (image ); %>