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35 changes: 18 additions & 17 deletions posts/2025-09-23-25.0.0.10-beta.adoc
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Expand Up @@ -6,8 +6,8 @@ categories: blog
author_picture: https://avatars3.githubusercontent.com/IsmathBadsha
author_github: https://github.com/IsmathBadsha
seo-title: Support for override library in the application classloader and support for Java 25 in 25.0.0.10-beta - OpenLiberty.io
seo-description: Support for override library in the application classloader to fix the application without requiring the application to be rebuilt and Java 25 compatibility are introduced in 25.0.0.10-beta.
blog_description: Support for override library in the application classloader to fix the application without requiring the application to be rebuilt and Java 25 compatibility are introduced in 25.0.0.10-beta.
seo-description: Support for the override library in the application classloader that allows fixing applications without rebuilding them, and Java 25 compatibility are introduced in version 25.0.0.10-beta.
blog_description: Support for the override library in the application classloader that allows fixing applications without rebuilding them, and Java 25 compatibility are introduced in version 25.0.0.10-beta.
open-graph-image: https://openliberty.io/img/twitter_card.jpg
open-graph-image-alt: Open Liberty Logo
---
Expand Down Expand Up @@ -50,7 +50,7 @@ Ismath Badsha <https://github.com/IsmathBadsha>
// change the "IMAGE CAPTION" to a couple words of what the image is
// // // // // // // //

Support for override library in the application classloader to fix the application without requiring the application to be rebuilt and Java 25 compatibility are introduced in 25.0.0.10-beta.
Support for the override library in the application classloader that allows fixing applications without rebuilding them, and Java 25 compatibility are introduced in version 25.0.0.10-beta.

// // // // // // // //
// Change the RELEASE_SUMMARY to an introductory paragraph. This sentence is really
Expand Down Expand Up @@ -82,9 +82,9 @@ See also link:{url-prefix}/blog/?search=beta&key=tag[previous Open Liberty beta
[#overrideLibrary]
== OverrideLibrary support for application classloader

The 25.0.0.10-beta release introduces a new type of library reference for configuring an application's `<classloader/>`. This new reference type is called an override library reference. An override library reference works similarly to a private library reference, where class instances remain unique to the application's classloader. However, the key difference is in the search order, the override library class path is searched before the application’s own class path.This allows the library path to override classes that are already contained within the application.
The 25.0.0.10-beta release introduces a new type of library reference for configuring an application’s `<classloader/>`: the override library reference. The override library reference is similar to a private library reference because class instances remain unique to the application’s classloader. The key difference is the search order. With an override library reference, the library class path is searched before the application’s own class path, which allows the library path to override classes that are already included in the application.

For example, when a `<webApplication/>` contains a class like `org.acme.needs.fix.SomeImpl` that needs to be overridden in order to fix an issue, but rebuilding the application to include the fix is difficult or undesirable,as a new library JAR (e.g., someImplFix.jar) is built to include the corrected class files. Then the following `server.xml` could be used to configure an `overrideLibraryRef` to fix the application without requiring the application to be rebuilt:
For example, suppose a `<webApplication/>` contains a class such as `org.acme.needs.fix.SomeImpl` that must be overridden to resolve an issue. If rebuilding the application to include the fix is difficult or undesirable, you can instead build a new library JAR (for example, someImplFix.jar) with the corrected class files. The following `server.xml` configuration shows how to use an `overrideLibraryRef` to apply the fix without rebuilding the application:

[source, xml]
----
Expand All @@ -107,11 +107,10 @@ For example, when a `<webApplication/>` contains a class like `org.acme.needs.fi
[#beta_support_java25]
== Beta support for Java 25

Java 25 is the latest version of Java and a Long-Term-Support (LTS) release. It contains many new features and enhancements over previous versions of Java.
Java 25, the latest Long-Term Support (LTS) release, contains many new features and enhancements over previous versions of Java.
There are 18 new features (JEPs) in link:https://openjdk.org/projects/jdk/25/[Java 25]: 6 are test features and 12 are fully delivered.

There are 18 new features (JEPs) in link:https://openjdk.org/projects/jdk/25/[Java 25]. Six are test features and twelve are fully delivered:

Test features:
**Test features**

* 470: link:https://openjdk.org/jeps/470[PEM Encodings of Cryptographic Objects (Preview)]
* 502: link:https://openjdk.org/jeps/502[Stable Values (Preview)]
Expand All @@ -120,7 +119,7 @@ Test features:
* 508: link:https://openjdk.org/jeps/508[Vector API (Tenth Incubator)]
* 509: link:https://openjdk.org/jeps/509[JFR CPU-Time Profiling (Experimental)]

Delivered features:
**Delivered features**

* 503: link:https://openjdk.org/jeps/503[Remove the 32-bit x86 Port]
* 506: link:https://openjdk.org/jeps/506[Scoped Values]
Expand All @@ -135,15 +134,17 @@ Delivered features:
* 520: link:https://openjdk.org/jeps/520[JFR Method Timing & Tracing]
* 521: link:https://openjdk.org/jeps/521[Generational Shenandoah]

An important note about using the `CompletableFuture` and `SubmissionPublisher` classes in Java 25 JDK is that if there is no explicit Executor backing these classes, by default `ForkJoinPool.commonPool` will be used. The pool defaults to a parallelism value equal to the number of available processors minus 1 (# available processors - 1). If the application runs in an environment with 2 (or fewer) processors, there is a possibility of running into concurrency issue since Java 25 uses only 1 thread by default. This was not an issue in earlier versions of Java as the JDK would overlook the parallelism value and create an additional thread.
When you use the `CompletableFuture` and `SubmissionPublisher` classes in Java 25 without an explicit Executor backing these classes, they default to using `ForkJoinPool.commonPool`. This pool sets its parallelism value to the number of available processors minus one (# available processors - 1). If the application runs on a system with two or fewer processors, there is a possibility of running into concurrency issues as Java 25 uses only a single thread by default. In earlier Java versions, this was not a problem because the JDK overlooked the parallelism value and created an additional thread.

The above issue can be avoided by following the below steps:
You can avoid this issue by using one of the following approaches:

. Use the `CompletableFuture` provided in Liberty's Jakarta Concurrency implementation, which does not have this issue. An easy way to do that is with a link:https://www.ibm.com/docs/en/was-liberty/core?topic=manually-configuring-managed-executors[DefaultManagedExecutorService] and using link:https://jakarta.ee/specifications/concurrency/3.1/apidocs/jakarta.concurrency/jakarta/enterprise/concurrent/managedexecutorservice#supplyAsync(java.util.function.Supplier[supplyAsync or runAsync]).
. Use the `CompletableFuture` provided in Liberty’s Jakarta Concurrency implementation, which does not have this limitation. An easy way to do this is with a link:https://www.ibm.com/docs/en/was-liberty/core?topic=manually-configuring-managed-executors[DefaultManagedExecutorService] and the link:https://jakarta.ee/specifications/concurrency/3.1/apidocs/jakarta.concurrency/jakarta/enterprise/concurrent/managedexecutorservice#supplyAsync(java.util.function.Supplier)[supplyAsync or runAsync] methods.
. Explicitly set the `ForkJoinPool.commonPool` parallelism value to whatever you need, `-Djava.util.concurrent.ForkJoinPool.common.parallelism=N` (where N is the minimum number of threads needed)
. Use an explicit backing Executor
. Explicitly set the `ForkJoinPool.commonPool` parallelism value to the desired number of threads by using the system property,
`-Djava.util.concurrent.ForkJoinPool.common.parallelism=N` (where N is the minimum number of threads required).
. Use an explicit backing `Executor`.

For more information about this change, please reference the following links:
For more information on this change, see the following links:
https://bugs.openjdk.org/browse/JDK-8362881
https://bugs.openjdk.org/browse/JDK-8319447
https://bugs.openjdk.org/browse/JDK-8360593
Expand All @@ -152,8 +153,8 @@ Take advantage of the changes in Java 25 in Open Liberty now and get more time t

Just link:https://jdk.java.net/25/[download the latest release of Java 25], download and install the link:https://openliberty.io/downloads/#runtime_betas[25.0.0.10-beta] version of Open Liberty, edit your Liberty server's link:https://openliberty.io/docs/latest/reference/config/server-configuration-overview.html#server-env[server.env] file with JAVA_HOME set to your Java 25 installation directory and start testing!

For more information on Java 25, please visit the Java 25 link:https://jdk.java.net/25/release-notes[release notes page], link:https://download.java.net/java/early_access/jdk25/docs/api/[API Javadoc page] or link:https://jdk.java.net/25/[download page].
For more information on Open Liberty, please visit our link:https://openliberty.io/docs[documentation page].
For more information on Java 25, see the Java 25 link:https://jdk.java.net/25/release-notes[release notes page], link:https://download.java.net/java/early_access/jdk25/docs/api/[API Javadoc page] or link:https://jdk.java.net/25/[download page].
For more information on Open Liberty,see our link:https://openliberty.io/docs[documentation page].


// DO NOT MODIFY THIS LINE. </GHA-BLOG-TOPIC>
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