Use HTTPS when linking to groovy-lang.org

Closes gh-21466

spring-boot-project/spring-boot-docs/src/main/asciidoc/getting-started.adoc

@@ -218,7 +218,7 @@ More details on getting started with Spring Boot and Gradle can be found in the
 [[getting-started-installing-the-cli]]
 === Installing the Spring Boot CLI
 The Spring Boot CLI (Command Line Interface) is a command line tool that you can use to quickly prototype with Spring.
-It lets you run http://groovy-lang.org/[Groovy] scripts, which means that you have a familiar Java-like syntax without so much boilerplate code.
+It lets you run https://groovy-lang.org/[Groovy] scripts, which means that you have a familiar Java-like syntax without so much boilerplate code.
 
 You do not need to use the CLI to work with Spring Boot, but it is definitely the quickest way to get a Spring application off the ground.
 

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -2149,7 +2149,7 @@ Also, many other templating engines include their own Spring MVC integrations.
 Spring Boot includes auto-configuration support for the following templating engines:
 
  * https://freemarker.apache.org/docs/[FreeMarker]
- * http://docs.groovy-lang.org/docs/next/html/documentation/template-engines.html#_the_markuptemplateengine[Groovy]
+ * https://docs.groovy-lang.org/docs/next/html/documentation/template-engines.html#_the_markuptemplateengine[Groovy]
  * https://www.thymeleaf.org[Thymeleaf]
  * https://mustache.github.io/[Mustache]
 

spring-boot-samples/spring-boot-sample-web-groovy-templates/README.adoc

@@ -1,5 +1,5 @@
 This sample application uses Spring Boot and
-http://docs.groovy-lang.org/latest/html/documentation/#_the_markuptemplateengine[Groovy templates]
+https://docs.groovy-lang.org/latest/html/documentation/#_the_markuptemplateengine[Groovy templates]
 in the View layer. The templates for this app live in `classpath:/templates/`, which is
 the conventional location for Spring Boot. External configuration is available via
 ``spring.groovy.template.*''.

spring-boot-samples/spring-boot-sample-web-groovy-templates/src/main/resources/templates/layout.tpl

@@ -8,7 +8,7 @@ html {
       div(class:'navbar') {
         div(class:'navbar-inner') {
           a(class:'brand',
-              href:'http://docs.groovy-lang.org/docs/latest/html/documentation/markup-template-engine.html') {
+              href:'https://docs.groovy-lang.org/docs/latest/html/documentation/markup-template-engine.html') {
               yield 'Groovy - Layout'
           }
           ul(class:'nav') {

src/checkstyle/nohttp-whitelist.txt

@@ -1,6 +1,4 @@
-^http://docs.groovy-lang.org.*
 ^http://exslt.org/common.*
-^http://groovy-lang.org.*
 ^http://hsqldb.org.*
 ^http://livereload.com/.*
 ^http://www.jdotsoft.com.*