Set alerting plugin 3.0.0 baseline JDK version to JDK-21 (#1695)

Signed-off-by: Andriy Redko <[email protected]>

Author: reta

.github/workflows/bwc-test-workflow.yml

@@ -19,7 +19,7 @@ jobs:
     needs: Get-CI-Image-Tag
     strategy:
       matrix:
-        java: [ 11 ]
+        java: [ 21 ]
     # Job name
     name: Build and test Alerting
     # This job runs on Linux

DEVELOPER_GUIDE.md

@@ -1,8 +1,7 @@
 - [Developer Guide](#developer-guide)
   - [Forking and Cloning](#forking-and-cloning)
   - [Install Prerequisites](#install-prerequisites)
-    - [JDK 11](#jdk-11)
-    - [JDK 14](#jdk-14)
+    - [JDK 21](#jdk-21)
   - [Setup](#setup)
   - [Build](#build)
     - [Building from the command line](#building-from-the-command-line)
@@ -19,32 +18,28 @@ Fork this repository on GitHub, and clone locally with `git clone`.
 
 ### Install Prerequisites
 
-#### JDK 11
+#### JDK 21
 
-OpenSearch builds using Java 11 at a minimum, using the Adoptium distribution. 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`. This is configured in [buildSrc/build.gradle](buildSrc/build.gradle) and [distribution/tools/java-version-checker/build.gradle](distribution/tools/java-version-checker/build.gradle).
+OpenSearch builds using Java 21 at a minimum, using the Adoptium distribution. 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-11`. This is configured in [buildSrc/build.gradle](buildSrc/build.gradle) and [distribution/tools/java-version-checker/build.gradle](distribution/tools/java-version-checker/build.gradle).
 
 ```
 allprojects {
-  targetCompatibility = JavaVersion.VERSION_11
-  sourceCompatibility = JavaVersion.VERSION_11
+  targetCompatibility = JavaVersion.VERSION_21
+  sourceCompatibility = JavaVersion.VERSION_21
 }
 ```
 
 ```
-sourceCompatibility = JavaVersion.VERSION_11
-targetCompatibility = JavaVersion.VERSION_11
+sourceCompatibility = JavaVersion.VERSION_21
+targetCompatibility = JavaVersion.VERSION_21
 ```
 
-Download Java 11 from [here](https://adoptium.net/releases.html?variant=openjdk11).
-
-#### JDK 14
-
-To run the full suite of tests, download and install [JDK 14](https://jdk.java.net/archive/) and set `JAVA11_HOME`, and `JAVA14_HOME`. They are required by the [backwards compatibility test](./TESTING.md#testing-backwards-compatibility).
+Download Java 21 from [here](https://adoptium.net/releases.html?variant=openjdk21).
 
 ### Setup
 
 1. Clone the repository (see [Forking and Cloning](#forking-and-cloning))
-2. Make sure `JAVA_HOME` is pointing to a Java 11 JDK (see [Install Prerequisites](#install-prerequisites))
+2. Make sure `JAVA_HOME` is pointing to a Java 21 JDK (see [Install Prerequisites](#install-prerequisites))
 3. Launch Intellij IDEA, Choose Import Project and select the settings.gradle file in the root of this package.
 
 ### Build