Upgrade min JDK compatibility to JDK 21

CHANGELOG.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Bug Fixes
 ### Infrastructure
 * Removed JDK 11 and 17 version from CI runs [#1921](https://github.com/opensearch-project/k-NN/pull/1921)
+* Upgrade min JDK compatibility to JDK 21 [#2422](https://github.com/opensearch-project/k-NN/pull/2422)
 ### Documentation
 ### Maintenance
 ### Refactoring

DEVELOPER_GUIDE.md

@@ -2,7 +2,7 @@
   - [Getting Started](#getting-started)
     - [Fork OpenSearch k-NN Repo](#fork-opensearch-k-nn-repo)
     - [Install Prerequisites](#install-prerequisites)
-      - [JDK 11](#jdk-11)
+      - [JDK 21](#jdk-21)
       - [CMake](#cmake)
       - [Faiss Dependencies](#Faiss-Dependencies)
       - [Environment](#Environment)
@@ -39,23 +39,20 @@ git clone https://github.com/[your username]/OpenSearch.git
 
 ### Install Prerequisites
 
-#### JDK 11
+#### JDK 21
 
-OpenSearch builds using Java 11 at a minimum. This means you must have a JDK 11 installed with the environment variable 
-`JAVA_HOME` referencing the path to Java home for your JDK 11 installation, e.g. `JAVA_HOME=/usr/lib/jvm/jdk-11`.
+OpenSearch builds using Java 21 at a minimum. This means you must have a JDK 21 installed with the environment variable 
+`JAVA_HOME` referencing the path to Java home for your JDK 21 installation, e.g. `JAVA_HOME=/usr/lib/jvm/jdk-21`.
 
-One easy way to get Java 11 on *nix is to use [sdkman](https://sdkman.io/).
+One easy way to get Java 21 on *nix is to use [sdkman](https://sdkman.io/).
 
 ```bash
 curl -s "https://get.sdkman.io" | bash
 source ~/.sdkman/bin/sdkman-init.sh
-sdk install java 11.0.2-open
-sdk use java 11.0.2-open
+sdk install java 21.0.2-open
+sdk use java 21.0.2-open
 ```
 
-Team has to replace minimum JDK version 14 as it was not an LTS release. JDK 14 should still work for most scenarios.
-In addition to this, the plugin has been tested with JDK 17, and this JDK version is fully supported.
-
 #### CMake
 
 The plugin requires that cmake >= 3.24.0 is installed in order to build the JNI libraries.
@@ -201,10 +198,10 @@ Please follow these formatting guidelines:
 OpenSearch k-NN uses a [Gradle](https://docs.gradle.org/6.6.1/userguide/userguide.html) wrapper for its build. 
 Run `gradlew` on Unix systems.
 
-Tests use `JAVA11_HOME` environment variable, make sure to add it in the export path else the tests might fail. 
+Tests use `JAVA21_HOME` environment variable, make sure to add it in the export path else the tests might fail. 
 e.g 
 ```
-echo "export JAVA11_HOME=<JDK11 path>" >> ~/.zshrc
+echo "export JAVA21_HOME=<JDK21 path>" >> ~/.zshrc
 source ~/.zshrc
 ```
 

build.gradle

@@ -192,7 +192,7 @@ allprojects {
     }
     apply from: rootProject.file('build-tools/repositories.gradle').absoluteFile
     plugins.withId('java') {
-        sourceCompatibility = targetCompatibility = "11"
+        sourceCompatibility = targetCompatibility = "21"
     }
 
     afterEvaluate {

qa/build.gradle

@@ -46,6 +46,13 @@ if (Os.isFamily(Os.FAMILY_WINDOWS)) {
     file_ext = "zip"
 }
 
+allprojects {
+    java {
+        sourceCompatibility = JavaVersion.VERSION_21
+        targetCompatibility = JavaVersion.VERSION_21
+    }
+}
+
 // Task to pull k-NN plugin from archive
 task pullBwcPlugin {
     doFirst {