Integrate checkstyle

Issue gh-10

etc/checkstyle/checkstyle.xml

@@ -0,0 +1,51 @@
+<?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 -->
+	<module name="SuppressionFilter">
+		<property name="file" value="${config_loc}/suppressions.xml"/>
+	</module>
+
+	<!-- Root Checks -->
+	<module name="RegexpHeader">
+		<property name="headerFile" value="${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>
+</module>

etc/checkstyle/header.txt

@@ -0,0 +1,16 @@
+^\Q/*\E$
+^\Q * Copyright\E (\d{4}(\-\d{4})? the original author or authors\.|(\d{4}, )*(\d{4}) Acegi Technology Pty Limited)$
+^\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$
+^\Q * You may obtain a copy of the License at\E$
+^\Q *\E$
+^\Q *      https://www.apache.org/licenses/LICENSE-2.0\E$
+^\Q *\E$
+^\Q * Unless required by applicable law or agreed to in writing, software\E$
+^\Q * distributed under the License is distributed on an "AS IS" BASIS,\E$
+^\Q * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\E$
+^\Q * See the License for the specific language governing permissions and\E$
+^\Q * limitations under the License.\E$
+^\Q */\E$
+^.*$

etc/checkstyle/suppressions.xml

@@ -0,0 +1,19 @@
+<?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>