feat: Migrate to Java 21 (#2412)

Signed-off-by: Naydenov <nikola.naydenov@limechain.tech>
Signed-off-by: Ivan Ivanov <ivanivanov.ii726@gmail.com>
Co-authored-by: Ivan Ivanov <ivanivanov.ii726@gmail.com>

Author: naydenovn

.github/workflows/build.yml

@@ -51,7 +51,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1
@@ -169,7 +169,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1
@@ -224,7 +224,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Android SDK
         uses: android-actions/setup-android@9fc6c4e9069bf8d3d10b2204b1fb8f6ef7065407 # v3.2.2
@@ -279,7 +279,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1

.github/workflows/pages.yml

@@ -36,7 +36,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1

.github/workflows/release-artifacts.yml

@@ -52,7 +52,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1
@@ -114,7 +114,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1

.github/workflows/snyk-monitor.yml

@@ -28,7 +28,7 @@ jobs:
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
           distribution: temurin
-          java-version: "17.0.13"
+          java-version: "21.0.6"
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1

examples/gradle/toolchain-versions.properties

@@ -1 +1,3 @@
-jdk=17.0.13
+# SPDX-License-Identifier: Apache-2.0
+
+jdk=21.0.6

gradle/toolchain-versions.properties

@@ -1 +1,3 @@
-jdk=17.0.13
+# SPDX-License-Identifier: Apache-2.0
+
+jdk=21.0.6

sdk/src/main/java/com/hedera/hashgraph/sdk/Client.java

@@ -25,14 +25,7 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.CompletionStage;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.LinkedBlockingQueue;
-import java.util.concurrent.ThreadPoolExecutor;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
+import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;