A DESCRIPTION OF THE REQUEST :
Currently, there is no way for a Web Start application to specify that it is only compatible with a 32-bit JRE, or that it requires a 64-bit JRE. If a user has installed both 32-bit and 64-bit versions of JavaSE at the same release level, the JRE that will actually be used when launching a Web Start application is indeterminate. The application might launch with a 32-bit data model, or a 64-bit data model.

The Web Start developer guide describes a "-d32" option for vm-args, but as discussed in bug 6907802, the feature is only supported on Solaris and even if it were supported on Windows, it would still fall short because it will only use a 32 bit JRE "if available". What is needed is a way to require a 32 bit JRE, even if one is not currently installed. It may also be necessary for some applications to require a 64-bit JRE even if one is not currently installed.

JUSTIFICATION :
Web Start applications that depend on JNI libraries need to specify which data model should be used if the appropriate JNI libraries are only available in one data model. This is primarily a concern for older applications that depend on 32-bit libraries and need to require a 32-bit JRE.

It may also be the case that some applications have design requirements that depend on a 64-bit data model and would not be able to function in a 32-bit environment. These applications need a way to specify that they should be launched in a 64-bit JRE.



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
When both 32-bit and 64-bit JRE's are installed, if the JNLP file specifies only one data model or a preferred data model, that is the data model that is used. If the JNLP file does not indicate a requirement or a preference, then one data model or the other should be the consistent default choice.
ACTUAL -
Currently, the behavior is inconsistent (it appears that it might depend on which JRE was installed last). Your application may launch on the 32-bit JRE, or the 64-bit JRE, and there is no way to control this.

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N/A. This RFE is pointing out a gap in the JNLP spec.
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CUSTOMER SUBMITTED WORKAROUND :
1) Refrain from installing a 64-bit JRE if you have an application that requires a 32-bit JRE. Refrain from installing a 32-bit JRE if you have an application that requires a 64-bit JRE.

2) It appears that whichever JRE was installed last might influence this behavior, but to the extent that this is true, that mode of control is not sufficient to accommodate the needs of various applications that require one data model or the other.