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274

Chapter 12 Including Files and Applets in JSP Documents

12.3 Including Applets for the Java 

Plug In

With JSP, you don't need any special syntax to include ordinary applets: just

use the normal HTML 

APPLET

 tag. However, these applets must use JDK 1.1

or JDK 1.02 since neither Netscape 4.x nor Internet Explorer 5.x support the

Java 2 platform (i.e., JDK 1.2). This lack of support imposes several restric 

tions on applets:

In order to use Swing, you must send the Swing files over the 

network. This process is time consuming and fails in Internet 

Explorer 3 and Netscape 3.x and 4.01 4.05 (which only support 

JDK 1.02), since Swing depends on JDK 1.1. 

You cannot use Java 2D.

You cannot use the Java 2 collections package.

Your code runs more slowly, since most compilers for the Java 2 

platform are significantly improved over their 1.1 predecessors.

Furthermore, early browser releases had a number of inconsistencies in

the way they supported various AWT components, making testing and deliv 

ery of complex user interfaces more burdensome than it ought to have been.

To address this problem, Sun developed a browser plug in for Netscape and

Internet Explorer that lets you use the Java 2 platform for applets in a variety

of browsers. This plug in is available at 

http://java.sun.com/prod 

ucts/plugin/

, and also comes bundled with JDK 1.2.2 and later. Since the

plug in is quite large (several megabytes), it is not reasonable to expect users

on the WWW at large to download and install it just to run your applets. On

the other hand, it is a reasonable alternative for fast corporate intranets, espe 

cially since applets can automatically prompt browsers that lack the plug in to

download it.

Unfortunately, however, the normal 

APPLET

 tag will not work with the

plug in, since browsers are specifically designed to use only their built in vir 

tual machine when they see 

APPLET

. Instead, you have to use a long and

messy 

OBJECT

 tag for Internet Explorer and an equally long 

EMBED

 tag for

Netscape. Furthermore, since you typically don't know which browser type

will be accessing your page, you have to either include both 

OBJECT

 and

EMBED

 (placing the 

EMBED

 within the 

COMMENT

 section of 

OBJECT

) or identify

the browser type at the time of the request and conditionally build the right

tag. This process is straightforward but tedious and time consuming.

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.