Specify JDK version. (#341)

Reverting Java 11 changes (3d8d0e5).

build.gradle

@@ -39,6 +39,7 @@ subprojects {
       'equalsverifier': '3.8.2',
       'guava':          '29.0-jre',
       'jackson':        '2.13.3',
+      'jdk':            '8',
       'jena':           '3.17.0',
       'jetty':          '9.4.14.v20181114',
       'jquery':         '3.3.1-1',
@@ -66,9 +67,6 @@ subprojects {
 
   check.dependsOn(javadoc)
 
-  sourceCompatibility = '1.8'
-  targetCompatibility = '1.8'
-
   repositories {
     mavenCentral()
     maven githubPackage.invoke("metafacture")
@@ -86,6 +84,18 @@ subprojects {
     toolVersion '8.44'
   }
 
+  java {
+    toolchain {
+      languageVersion = JavaLanguageVersion.of(versions.jdk)
+    }
+  }
+
+  tasks.withType(JavaExec) {
+    javaLauncher = javaToolchains.launcherFor {
+      languageVersion = java.toolchain.languageVersion
+    }
+  }
+
   tasks.withType(JavaCompile) {
     'all -processing -rawtypes -serial'.split().each {
       options.compilerArgs << "-Xlint:${it}"

metafix/src/test/java/org/metafacture/metafix/MetafixMethodTest.java

@@ -2310,7 +2310,7 @@ public void copyFieldToSubfieldOfArrayOfObjectsWithExplicitAppend() {
 
     @Test
     public void copyFieldToSubfieldOfArrayOfStringsWithIndexImplicitAppend() {
-        MetafixTestHelpers.assertProcessException(IndexOutOfBoundsException.class, "Index 0 out of bounds for length 0", () ->
+        MetafixTestHelpers.assertProcessException(IndexOutOfBoundsException.class, "Index: 0, Size: 0", () ->
             MetafixTestHelpers.assertFix(streamReceiver, Arrays.asList(
                     "set_array('test[]')",
                     "copy_field('key', 'test[].1')"

metafix/src/test/resources/org/metafacture/metafix/integration/record/fromJson/toJson/copy_fieldToArrayOfStringsWithIndex/expected.err

@@ -1,2 +1,2 @@
 ^Exception in thread "main" org\.metafacture\.metafix\.FixProcessException: Error while executing Fix expression \(at .*/metafix/src/test/resources/org/metafacture/metafix/integration/record/fromJson/toJson/copy_fieldToArrayOfStringsWithIndex/test\.fix, line 2\): copy_field\("key", "test\[\]\.1"\)$
-^Caused by: java\.lang\.IndexOutOfBoundsException: Index 0 out of bounds for length 0$
+^Caused by: java\.lang\.IndexOutOfBoundsException: Index: 0, Size: 0$

settings.gradle

@@ -1,3 +1,7 @@
+plugins {
+  id 'org.gradle.toolchains.foojay-resolver-convention' version '0.8.0'
+}
+
 include 'metafix'
 include 'metafix-ide'
 include 'metafix-runner'