Java Using Extensions or Other Packaged APIs

Java Using Extensions or Other Packaged APIs

Problem 

You have a JAR file of classes you want to use. 

Solution 

Simply copy the JAR into JDKHOME/jre/lib/ext/. 

Explained

The Java API has grown by leaps and bounds since its first public release in 1995. It is now considered sufficiently functional for writing robust applications, but the areas to which it is being applied continue to grow. Some specialized APIs may require more resources than you have on a given Java platform. Many of the new APIs from Sun are in the form of standard extensions, which is indicated by their package names beginning in javax.. Classes in packages named java. or javax. are treated as built-in classes by a web browser for purposes of applet security, for example. Each extension is distributed in the form of a JAR file (see Recipe 23.4). 

If you have a Java runtime that does not support this feature, you may need to add each JAR file to your CLASSPATH, as in Recipe 1.4. 

As you accumulate these and other optional APIs contained in JAR files, you can simply drop these JAR files into the Java Extensions Mechanism directory, typically something like \jdk1.4\jre\lib\ext., instead of listing each JAR file in your CLASSPATH variable and watching CLASSPATH grow and grow and grow. The runtime looks here for any and all JAR and zip files, so no special action is needed. In fact, unlike many other system changes, you do not even need to reboot your computer; this directory is scanned each time the JVM starts up. You may, however, need to restart a long-running program such as an IDE for it to notice the change. Try it and see first.