I have a script that starts Tomcat and it looks like this:
rem set JRE_HOME=C:\Program Files\Java\jdk1.7.0_03
set JRE_HOME=C:\Program Files\Java\jre7\
set CATALINA_HOME=D:\test\Server\apache-tomcat-6.0.18
"%CATALINA_HOME%\bin\catalina.bat" jpda start
I can set JRE_HOME to either my jre folder or my JDK folder and Tomcat will work, but if I remove JRE_HOME and use JAVA_HOME instead, Tomcat will only work if I give it the path to the JDK folder.
So what is the difference between JRE and JAVA home, why does Tomcat behave in this manner?
Tomcat enables some additional debugging options at start up if you are running with a full JDK. These options require the JDK so you Tomcat checks you are actually using one if you claim that you are to ensure these options don't fail if used.
I rarely see these options being used. I think I have used them once in getting on for 10 years working with Tomcat.
When you use JRE_HOME Tomcat doesn't enable JDK specific options so it doesn't check if you are running with the full JDK rather than the JRE.