Applications written for 1.5 should run under 1.6. JDK's so far have been backwards compatible.
I run several web and application servers, which do tend to be developed for a particular JDK. In that case I write a batch file to set the PATH and JAVA_HOME environment variables to a particular version.
Specify the absolute path of the java.exe or javaw.exe that you want to use. So instead of
Note how I added double quotes around the path - it is needed if there is a space somewhere in the path. Given that most people install the JRE and JDK in C:\Program Files, it's probably needed.
The java.exe and javaw.exe in C:\WINDOWS\system32 are nothing more than wrapper files. They check a part of the registry for the location of the JRE, then execute the java.exe / javaw.exe in that location. When you install a new JRE it changes the registry to say the new JRE should be used, but the old one can still be executed.
Apparently you can specify the JDK version in the JNLP file:
My application requires a specific version of the JRE. How do I specify this my JNLP file?
The tag <j2se version="versionNum"> specifies a platform version, where versionNum is 1.2, 1.3, 1.4, or 1.5.
You can request a specific product version by including a vendor URL in the href attribute. For Sun's JREs, the URL is http://java.sun.com/products/autodl/j2se For example, the following J2SE tag will request any Sun 1.3.1 implementation: