Sun Microsystem's Java 2 Platform Standard Edition 5.0 (J2SE 5.0), a.k.a Java 1.5, remains the recommended JVM to build and run Sakai. Certain files, such as *.jsp and *.jws, require compilation so downloading and attempting to use only the runtime environment (JRE 5.0) will not suffice.  Mac OS X includes the full version of Java J2SE 5.0, pre-installed with the Java Development Kit (JDK) and the HotSpot virtual machine (VM), so Mac users should not need to install Java.  If you find Sun's version and naming conventions confusing, see Sun Java SE Naming and Versions for an outline of their practices.

(minus) Oracle's Sun Java J2SE 5.0 (a.k.a Java 1.5) has completed the EOL process and is no longer supported. If are still running Java 1.5 please note that security vulnerabilities exist in JDK/JRE 5.0 updates 1.5.0_17 and earlier. Sun recommends that you install JDK/JRE 5.0 Update 18+ (the final update is JDK/JRE 5.0 Update 22).

(warning) Sakai 2.6 can be run using Java Platform, Standard Edition 6 (Java SE 6), a.k.a Java 1.6, although to-date there is little production experience that warrants recommending 2.6 users to upgrade their JVM. Should you choose to run Sakai in a Java 6 JVM you must (at a minimum) add the following environment setting to your JAVA_OPTS:

-Dsun.lang.ClassLoader.allowArraySyntax=true

To confirm that Java is both installed on your system and is the correct version for Sakai, run java -version from the command line:

java -version

If Java is installed, basic version and build information will be displayed:

java version "1.5.0_18"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_18-b02)
Java HotSpot(TM) Server VM (build 1.5.0_18-b02, mixed mode)

If Java is not installed or you are running the wrong version you can download the J2SE 5.0 JDK release from Sun's archive:

Release

Installation Notes

http://java.sun.com/javase/downloads/index_jdk5.jsp

http://java.sun.com/j2se/1.5.0/install.html

Install the SDK, typically in the /opt directory, i.e. /opt/java. Install the JRE in a different directory (usually the default directory, especially if running Windows) or you may experience run-time issues.