Gradle: use release flag instead of sourceCompatibility and targetCompatibility.

Fixes FlatBufferBuilder using ByteBuffer instead of Buffer API.

Author: greenrobot-team

objectbox-java-api/build.gradle

@@ -1,7 +1,10 @@
 apply plugin: 'java-library'
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
+// Note: use release flag instead of sourceCompatibility and targetCompatibility to ensure only JDK 8 API is used.
+// https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation
+compileJava {
+    options.release.set(8)
+}
 
 task javadocJar(type: Jar, dependsOn: javadoc) {
     archiveClassifier.set('javadoc')

objectbox-java/build.gradle

@@ -1,8 +1,11 @@
 apply plugin: 'java-library'
 apply plugin: "com.github.spotbugs"
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
+// Note: use release flag instead of sourceCompatibility and targetCompatibility to ensure only JDK 8 API is used.
+// https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation
+compileJava {
+    options.release.set(8)
+}
 
 ext {
     javadocForWebDir = "$buildDir/docs/web-api-docs"

objectbox-kotlin/build.gradle

@@ -5,8 +5,11 @@ buildscript {
 apply plugin: 'kotlin'
 apply plugin: 'org.jetbrains.dokka'
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
+// Note: use release flag instead of sourceCompatibility and targetCompatibility to ensure only JDK 8 API is used.
+// https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation
+compileJava {
+    options.release.set(8)
+}
 
 // Produce Java 8 byte code, would default to Java 6.
 tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {

objectbox-rxjava/build.gradle

@@ -1,7 +1,10 @@
 apply plugin: 'java-library'
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
+// Note: use release flag instead of sourceCompatibility and targetCompatibility to ensure only JDK 8 API is used.
+// https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation
+compileJava {
+    options.release.set(8)
+}
 
 dependencies {
     api project(':objectbox-java')

objectbox-rxjava3/build.gradle

@@ -6,8 +6,11 @@ apply plugin: 'java-library'
 apply plugin: 'kotlin'
 apply plugin: 'org.jetbrains.dokka'
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
+// Note: use release flag instead of sourceCompatibility and targetCompatibility to ensure only JDK 8 API is used.
+// https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation
+compileJava {
+    options.release.set(8)
+}
 
 // Produce Java 8 byte code, would default to Java 6.
 tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {

tests/objectbox-java-test/build.gradle

@@ -3,8 +3,11 @@ apply plugin: 'kotlin'
 
 uploadArchives.enabled = false
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
+// Note: use release flag instead of sourceCompatibility and targetCompatibility to ensure only JDK 8 API is used.
+// https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation
+compileJava {
+    options.release.set(8)
+}
 
 // Produce Java 8 byte code, would default to Java 6.
 tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {

tests/test-proguard/build.gradle

@@ -2,8 +2,11 @@ apply plugin: 'java-library'
 
 uploadArchives.enabled = false
 
-sourceCompatibility = JavaVersion.VERSION_1_8
-targetCompatibility = JavaVersion.VERSION_1_8
+// Note: use release flag instead of sourceCompatibility and targetCompatibility to ensure only JDK 8 API is used.
+// https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation
+compileJava {
+    options.release.set(8)
+}
 
 repositories {
     // Native lib might be deployed only in internal repo