Ensure single line of whitespace after header

Closes gh-194

Author: philwebb

spring-javaformat/spring-javaformat-checkstyle/src/main/java/io/spring/javaformat/checkstyle/check/SpringHeaderCheck.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2019 the original author or authors.
+ * Copyright 2017-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -77,6 +77,8 @@ public class SpringHeaderCheck extends AbstractFileSetCheck {
 
 	private URI packageInfoHeaderFile;
 
+	private boolean blankLineAfter = true;
+
 	private HeaderCheck check;
 
 	private HeaderCheck packageInfoCheck;
@@ -108,7 +110,7 @@ private HeaderCheck createCheck(String headerType, URI headerFile) throws IOExce
 
 	@Override
 	protected void processFiltered(File file, FileText fileText) throws CheckstyleException {
-		getCheck(file).run(fileText);
+		getCheck(file).run(fileText, this.blankLineAfter);
 	}
 
 	private HeaderCheck getCheck(File file) {
@@ -145,6 +147,10 @@ public void setPackageInfoHeaderFile(URI packageInfoHeaderFile) {
 		this.packageInfoHeaderFile = packageInfoHeaderFile;
 	}
 
+	public void setBlankLineAfter(boolean blankLineAfter) {
+		this.blankLineAfter = blankLineAfter;
+	}
+
 	/**
 	 * Interface used to check for a header.
 	 */
@@ -153,14 +159,15 @@ private interface HeaderCheck {
 		/**
 		 * Don't run any checks.
 		 */
-		HeaderCheck NONE = (fileText) -> true;
+		HeaderCheck NONE = (fileText, blankLineAfter) -> true;
 
 		/**
 		 * Run the check.
 		 * @param fileText the text to check
+		 * @param blankLineAfter if a blank line should be after the header
 		 * @return {@code true} if the header is valid
 		 */
-		boolean run(FileText fileText);
+		boolean run(FileText fileText, boolean blankLineAfter);
 
 	}
 
@@ -209,7 +216,7 @@ private Pattern loadLine(String line, String copyrightPattern) {
 		}
 
 		@Override
-		public boolean run(FileText fileText) {
+		public boolean run(FileText fileText, boolean blankLineAfter) {
 			if (this.lines.size() > fileText.size()) {
 				log(1, RegexpHeaderCheck.MSG_HEADER_MISSING);
 				return false;
@@ -222,6 +229,11 @@ public boolean run(FileText fileText) {
 					return false;
 				}
 			}
+			if (blankLineAfter) {
+				if (fileText.size() <= this.lines.size() || !"".equals(fileText.get(this.lines.size()))) {
+					log(this.lines.size() + 1, "header.blankLine");
+				}
+			}
 			return true;
 		}
 
@@ -233,7 +245,7 @@ public boolean run(FileText fileText) {
 	private class NoHeaderCheck implements HeaderCheck {
 
 		@Override
-		public boolean run(FileText fileText) {
+		public boolean run(FileText fileText, boolean blankLineAfter) {
 			for (int i = 0; i < fileText.size(); i++) {
 				String fileLine = fileText.get(i);
 				if (fileLine.trim().isEmpty()) {

spring-javaformat/spring-javaformat-checkstyle/src/main/resources/io/spring/javaformat/checkstyle/check/messages.properties

@@ -2,6 +2,7 @@ catch.singleLetter=Single letter catch variable (use "ex" instead).
 catch.wideEye=''o_O'' catch variable (use "ex" instead).
 header.unexpected=Unexpected header.
 header.mismatch=Line does not match expected header line of ''{0}''.
+header.blankLine=Blank line expected after header.
 hide.utility.class=Utility classes should not have a public or default constructor.
 import.avoidStatic=Using a static member import should be avoided - {0}.
 import.ordering=Wrong order for ''{0}'' import.

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/check/HeaderMissingBlankLine.txt

@@ -0,0 +1,2 @@
++Blank line expected after header
++1 error

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/config/HeaderMissingBlankLine.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0"?>
+<!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="io.spring.javaformat.checkstyle.SpringChecks">
+		<property name="headerFile" value="src/test/resources/customHeaderFile.txt"/>
+	</module>
+</module>

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/source/HeaderMissingBlankLine.java

@@ -0,0 +1,9 @@
+// (c) Somebody 2017-2019
+/**
+ * A custom header file.
+ *
+ * @author Phillip Webb
+ */
+public class HeaderMissingBlankLine {
+
+}