Update gradle, switch to kotlin-gradle and tidy up build-script

LICENSE_HEADER

@@ -0,0 +1,24 @@
+/*
+ * This file is part of BlueMap, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) Blue (Lukas Rieger) <https://bluecolored.de>
+ * Copyright (c) contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */

build.gradle

@@ -1,27 +0,0 @@
-plugins {
-	id 'java'
-	id 'java-library'
-}
-
-repositories {
-	jcenter()
-	mavenCentral()
-}
-
-dependencies {
-   api 'com.flowpowered:flow-math:1.0.3'
-}
-
-apply plugin: 'java'
-
-group = 'de.bluecolored.bluemap.api'
-version = apiVersion
-
-javadoc {
-	options {
-		links += [
-			'https://docs.oracle.com/javase/8/docs/api/',
-			'https://javadoc.io/doc/com.flowpowered/flow-math/1.0.3/'
-		]
-	}
-}

build.gradle.kts

@@ -0,0 +1,56 @@
+plugins {
+	java
+	`java-library`
+	id("com.diffplug.spotless") version "6.1.2"
+}
+
+group = "de.bluecolored.bluemap.api"
+
+val apiVersion: String by project
+version = apiVersion
+
+val javaTarget = 8
+java {
+	sourceCompatibility = JavaVersion.toVersion(javaTarget)
+	targetCompatibility = JavaVersion.toVersion(javaTarget)
+}
+
+repositories {
+	mavenCentral()
+}
+
+dependencies {
+   api ("com.flowpowered:flow-math:1.0.3")
+}
+
+spotless {
+	java {
+		target ("src/*/java/**/*.java")
+
+		licenseHeaderFile("LICENSE_HEADER")
+		indentWithSpaces()
+		trimTrailingWhitespace()
+	}
+}
+
+tasks.withType(JavaCompile::class).configureEach {
+	options.apply {
+		encoding = "utf-8"
+	}
+}
+
+tasks.withType(AbstractArchiveTask::class).configureEach {
+	isReproducibleFileOrder = true
+	isPreserveFileTimestamps = false
+}
+
+tasks.javadoc {
+	options {
+		this as StandardJavadocDocletOptions
+
+		links(
+			"https://docs.oracle.com/javase/8/docs/api/",
+			"https://javadoc.io/doc/com.flowpowered/flow-math/1.0.3/"
+		)
+	}
+}

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.0.2-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.3.3-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists