Apply Spring checkstyle conventions

Issue gh-1624

etc/checkstyle/checkstyle-suppressions.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<!DOCTYPE suppressions PUBLIC
+		"-//Checkstyle//DTD SuppressionFilter Configuration 1.2//EN"
+		"https://checkstyle.org/dtds/suppressions_1_2.dtd">
+<suppressions>
+	<suppress files=".*" checks="JavadocStyle" />
+	<suppress files="SpringAuthorizationServerVersion\.java" checks="HideUtilityClassConstructor"/>
+</suppressions>

etc/checkstyle/checkstyle.xml

@@ -1,51 +1,18 @@
 <?xml version="1.0"?>
-<!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
-		"https://www.puppycrawl.com/dtds/configuration_1_3.dtd">
-<module name="Checker">
-	<!-- Suppressions -->
+<!DOCTYPE module PUBLIC
+		"-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+		"https://checkstyle.org/dtds/configuration_1_3.dtd">
+<module name="com.puppycrawl.tools.checkstyle.Checker">
 	<module name="SuppressionFilter">
-		<property name="file" value="${config_loc}/suppressions.xml"/>
+		<property name="file"
+				  value="${config_loc}/checkstyle-suppressions.xml" />
 	</module>
-
-	<!-- Root Checks -->
-	<module name="RegexpHeader">
-		<property name="headerFile" value="${config_loc}/header.txt"/>
-		<property name="fileExtensions" value="java"/>
+	<module name="com.puppycrawl.tools.checkstyle.checks.header.RegexpHeaderCheck">
+		<property name="headerFile" value="${config_loc}/header.txt" />
+		<property name="fileExtensions" value="java" />
 	</module>
-
-	<!-- Root Checks -->
-	<module name="TreeWalker">
-		<!-- Annotations -->
-		<module name="MissingOverrideCheck" />
-
-		<!-- Coding -->
-		<module name="EmptyStatementCheck" />
-		<module name="RedundantModifier" />
-
-		<!-- Imports -->
-		<module name="UnusedImportsCheck">
-			<property name="processJavadoc" value="true" />
-		</module>
-
-		<!-- Regexp -->
-		<module name="RegexpSinglelineJava">
-			<property name="format" value="^\t* +\t*\S"/>
-			<property name="message" value="Line has leading space characters; indentation should be performed with tabs only."/>
-			<property name="ignoreComments" value="true"/>
-		</module>
-		<module name="RegexpSinglelineJava">
-			<property name="maximum" value="0"/>
-			<property name="format" value="org\.junit\.Assert\.assert"/>
-			<property name="message" value="Please use AssertJ imports."/>
-			<property name="ignoreComments" value="true"/>
-		</module>
-		<module name="Regexp">
-			<property name="format" value="[ \t]+$"/>
-			<property name="illegalPattern" value="true"/>
-			<property name="message" value="Trailing whitespace"/>
-		</module>
-
-		<!-- Whitespace -->
-		<module name="WhitespaceAfterCheck" />
+	<module name="io.spring.javaformat.checkstyle.SpringChecks">
+		<property name="excludes" value="io.spring.javaformat.checkstyle.check.SpringHeaderCheck" />
+		<property name="excludes" value="com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocPackageCheck" />
 	</module>
 </module>

etc/checkstyle/header.txt

@@ -1,5 +1,5 @@
 ^\Q/*\E$
-^\Q * Copyright\E (\d{4}(\-\d{4})? the original author or authors\.|(\d{4}, )*(\d{4}) Acegi Technology Pty Limited)$
+^\Q * Copyright \E20\d\d\-20\d\d\Q the original author or authors.\E$
 ^\Q *\E$
 ^\Q * Licensed under the Apache License, Version 2.0 (the "License");\E$
 ^\Q * you may not use this file except in compliance with the License.\E$

etc/checkstyle/suppressions.xml

@@ -1,19 +0,0 @@
-<?xml version="1.0"?>
-<!DOCTYPE suppressions PUBLIC "-//Puppy Crawl//DTD Suppressions 1.1//EN"
-		"https://www.puppycrawl.com/dtds/suppressions_1_1.dtd">
-<suppressions>
-	<suppress files=".+Application\.java" checks="HideUtilityClassConstructor"/>
-	<suppress files=".+Configuration\.java" checks="HideUtilityClassConstructor"/>
-	<suppress files="[\\/]BCrypt(Tests)?\.java" checks="RegexpHeader"/>
-
-	<suppress files="[\\/]src[\\/]test[\\/]java[\\/]" checks="Javadoc"/>
-	<suppress files="[\\/]src[\\/]integration-test[\\/]java[\\/]" checks="Javadoc"/>
-
-	<suppress files="[\\/]docs[\\/]" checks="Javadoc"/>
-	<suppress files="[\\/]docs[\\/]" checks="CommentsIndentation"/>
-	<suppress files="[\\/]docs[\\/]" checks="InnerTypeLast"/>
-
-	<suppress files="[\\/]samples[\\/]" checks="Javadoc"/>
-	<suppress files="[\\/]samples[\\/]" checks="CommentsIndentation"/>
-	<suppress files="[\\/]samples[\\/]" checks="InnerTypeLast"/>
-</suppressions>