Does tycho build ignore justj JRE version request?

[Dani-Hub]

Since recently we switched to the headless tycho build following the layout described here:

https://tycho.eclipseprojects.io/doc/latest/StructuredBuild.html

I should point out that the tycho build only generates an executable (Because the target platform completely defines the content), so our target platform file just looks like this:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<?pde version="3.8"?>
<target name="target-platform">
    <locations>
        <location path="target/thirdparty" type="Directory"/>
    </locations>
</target>

Now we try to use an embedded Java-17 JRE by the modifying our the tycho build as shown below. In general it works (The embedded JRE is produced in the final product), but the issue is, that instead of the requested Java-17 we always get a Java-21 JRE, despite the fact that our product is based on an Eclipse 4.26. Here is what we have done so far:

1. We specify

<repositories>
    <repository>
        <id>justj</id>
        <url>https://download.eclipse.org/justj/jres/17/updates/release/17.0.14/</url>
        <layout>p2</layout>
    </repository>
</repositories>

(Note: We are aware that https://download.eclipse.org/justj/jres/17/updates/release/latest/ is generally better, because we would be happy to get the most recent Java-17 JRE, but I'm trying to demonstrate that even a specific version seems to be ignored)

2. In the target-platform-configuration plugin configuration we have:

<plugin>
        <groupId>org.eclipse.tycho</groupId>
        <artifactId>target-platform-configuration</artifactId>
        <version>${tycho.version}</version>
        <configuration>
                <executionEnvironment>org.eclipse.justj.openjdk.hotspot.jre.full-17</executionEnvironment>
                <target>
                        <file>../target-definition/target-platform.target</file>
                </target>
                <environments>
                        <environment>
                                <os>win32</os>
                                <ws>win32</ws>
                                <arch>x86_64</arch>
                        </environment>
                </environments>
        </configuration>
</plugin>

3. In the feature-based product file we have the following two entries (where XXX denotes the normal product feature, irrelevant for the current purpose):

<vm>
   <windows include="false">org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-17</windows>
</vm>

<features>
   <feature id="XXX"/>
   <feature id="org.eclipse.justj.openjdk.hotspot.jre.full" version="17.0.14.v20250130-2147" match="perfect" installMode="root"/>
</features>

(I'm not sure whether the "match" element is actually supported here. Originally we had used
, but I used above technique to test whether enforcing a specific Java-17 JRE works
)

Now what I don't understand is why we get always an embedded Java-21 JRE albeit we attempt to enforce the requested JRE to be of type Java-17. Is there some other flag that needs to be set to ensure that a justj Java-17 JRE is used?

[laeubi]

The easiest way is to just set the "includeJRE" flag in the product and configure the justJ site here:

https://tycho.eclipseprojects.io/doc/latest/tycho-p2-director-plugin/materialize-products-mojo.html#productRepository

you don't need any special configuration, features or additonal sites.

[laeubi]

Remove everything from the feature and product and pom, only set this in the product:

then if you not want a "latest" (why?) then you can configure it in the

https://tycho.eclipseprojects.io/doc/latest/tycho-p2-director-plugin/materialize-products-mojo.html#productRepository

to e.g. only use Java 17.

[Dani-Hub]

Thanks, @laeubi : I can confirm that your suggestion fixed my problem!

[phermsdorf]

@laeubi bonus question to this setting:

after switching from defining the justj jre in the target file and including the justj feature in the product to this setting i see larger breaks in the build process when then build is at tycho-p2-director:4.0.13:materialize-products (create-product-distributions).

Does this resolving and/or artifact download is cached or reused somewhere? I looks like that is happening every time ...

We build several products in one build which all would use this with the same productRepository setting.

[laeubi]

Does this resolving and/or artifact download is cached or reused somewhere? I looks like that is happening every time ...

It should be cached, if something is downloaded you should see it in the logfile.

[phermsdorf]

Thx for your quick reply. I'll check that when beeing back from vacation ;)

[StephFo]

Hi,
By the way, to make it run on my side I have to declare this configuration:

                            <plugin>
			<groupId>org.eclipse.tycho</groupId>
			<artifactId>target-platform-configuration</artifactId>
			<version>${tycho-version}</version>
			<configuration>
				<executionEnvironment>JavaSE-21</executionEnvironment>
				<pomDependencies>consider</pomDependencies>
				<dependency-resolution>
					<localArtifacts>default</localArtifacts>
					<profileProperties>
						<org.eclipse.justj.buildtime>true</org.eclipse.justj.buildtime>
					</profileProperties>
				</dependency-resolution>

Without org.eclipse.justj.buildtime property, product assembly fails with conflicts about justj to include into the product.
Does anyone have an idea ?
I included this justj feature 'org.eclipse.justj.openjdk.hotspot.jre.full.stripped' to fetch relevant version for my app.
If I declare this feature as (root) in the product, justj 23 is included instead of 21.0.8 (at the moment)

Thanks

[laeubi]

See this demo for automatic JustJ inclusion:

https://github.com/eclipse-tycho/tycho/tree/main/demo/justj/automaticInstall

you can control the version by specify a specific updatesite here https://tycho.eclipseprojects.io/doc/latest/tycho-p2-director-plugin/materialize-products-mojo.html#productRepository

[StephFo]

Thank you very much for the pointers, it simplifies the configuration and it works perfectly.
Please note it includes non stripped full JRE.
Do we have product property to select JRE among : base, complete, full, full-stripped ?

[laeubi]

It just includes one JRE suitable for your product, there is currently no way to further restrict this. If you like you can try to propose a patch for supporting this, but due to how it currently works it is not that easy I guess.

[StephFo]

Thank you very much for your quick answers.

No need for a patch since it works doing:

1. include justj stripped feature 'org.eclipse.justj.openjdk.hotspot.jre.full.stripped' in .product as (root install)
2. add justj p2 repository with same url as in 'productRepository'
3. set profileProperties org.eclipse.justj.buildtime at true in configuration of tycho:target-platform-configuration plugin

👍