Java Custom JRE Support (Extensions)

[Stephan Bergmann]

On 16/09/2019 13:42, Rob Barry wrote:
> I've been developing an extension for LibreOffice in Java and have defaulted to targeting the v1.8
> JDK.
> 
> One issue I've noticed with this is that LibreOffice on Windows requires the x64 JRE in order to
> execute the extension. Given this is not the standard/suggested JRE download for windows it adds a
> bit of complication when a user attempts to install the extension.

Not sure what "the standard/suggested JRE download for windows" would 
be.  But note that LO runs the JVM in-process in its own soffice.bin 
process, so for a 32-bit LO installation the user needs to obtain a 
32-bit JRE, while for a 64-bit LO installation they need to obtain a 
64-bit JRE.

> One way I thought this could be fixed is to use the jlink (
> https://docs.oracle.com/en/java/javase/11/tools/jlink.html +
> https://blog.idrsolutions.com/2017/05/java-9-jlink-explained-in-5-minutes/) functionality which the
> JDK v9 ships with. Broadly speaking this allows the developer to create a custom JRE for the
> application which contains a sub-set of the modules contained in the standard JRE (so it's more
> performant + uses less memory). I've also read suggestions that Java development will be moving
> further in this direction with standard JREs not shipped by Oracle at all.
> 
> "Developers who deploy desktop applications to individual consumers (eg, games, personal banking, or
> other B2C applications) will need to transition to other deployment technologies such as the jlink
> and/or third party packaging and deployment solutions before the end of 2020." -
> https://www.oracle.com/technetwork/java/javase/javaclientroadmapupdate2018mar-4414431.pdf
> 
> This leads to my question: does LibreOffice have any support for the use of jlink custom-built JREs
> to build extensions?  Alternatively, are there any plans to support this in future?

There are no such plans by anyone I'm aware of at least.  As above, LO 
uses a single in-process JVM for all of its Java needs (from extensions 
and from whatever core components that use Java).