Configure a cache busting resource chain

This commit configures a resource chain with
`resources.chain.strategy.content.enabled`, enabling cache busting for
static resources based on the hash of their content.

A template helper (here a Groovy Closure) is added to the model given to
the view for appending hashes to static links such as:

    "/css/spring.css" -> "/css/spring-d35c4193cd32e7e44cda5737205c0c0e.css"

Fixes #321

initializr-service/src/main/groovy/io/spring/initializr/service/InitializrService.groovy

@@ -29,6 +29,7 @@ import org.springframework.context.annotation.Configuration
 import org.springframework.scheduling.annotation.AsyncConfigurerSupport
 import org.springframework.scheduling.annotation.EnableAsync
 import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor
+import org.springframework.web.servlet.resource.ResourceUrlProvider
 
 /**
  * Initializr service application. Enables legacy STS support for older
@@ -47,8 +48,9 @@ class InitializrService {
 	@Bean
 	@SuppressWarnings("deprecation")
 	LegacyStsController legacyStsController(InitializrMetadataProvider metadataProvider,
+											ResourceUrlProvider resourceUrlProvider,
 											GroovyTemplate groovyTemplate) {
-		new LegacyStsController(metadataProvider, groovyTemplate)
+		new LegacyStsController(metadataProvider, resourceUrlProvider, groovyTemplate)
 	}
 
 	@Configuration

initializr-service/src/main/resources/application.yml

@@ -13,6 +13,11 @@ spring:
   jackson:
     serialization:
      write-dates-as-timestamps: false
+  resources:
+    chain:
+      strategy:
+        content:
+          enabled: true
 
 initializr:
   env:

initializr-web/src/main/groovy/io/spring/initializr/web/autoconfigure/InitializrAutoConfiguration.groovy

@@ -16,6 +16,8 @@
 
 package io.spring.initializr.web.autoconfigure
 
+import org.springframework.web.servlet.resource.ResourceUrlProvider
+
 import java.util.concurrent.TimeUnit
 
 import com.github.benmanes.caffeine.cache.Caffeine
@@ -77,9 +79,11 @@ class InitializrAutoConfiguration {
 	@ConditionalOnMissingBean
 	MainController initializrMainController(InitializrMetadataProvider metadataProvider,
 											GroovyTemplate groovyTemplate,
+											ResourceUrlProvider resourceUrlProvider,
 											ProjectGenerator projectGenerator,
 											DependencyMetadataProvider dependencyMetadataProvider) {
-		new MainController(metadataProvider, groovyTemplate, projectGenerator, dependencyMetadataProvider)
+		new MainController(metadataProvider, groovyTemplate, resourceUrlProvider
+				, projectGenerator, dependencyMetadataProvider)
 	}
 
 	@Bean

initializr-web/src/main/groovy/io/spring/initializr/web/project/AbstractInitializrController.groovy

@@ -16,6 +16,8 @@
 
 package io.spring.initializr.web.project
 
+import org.springframework.web.servlet.resource.ResourceUrlProvider
+
 import javax.servlet.http.HttpServletResponse
 
 import io.spring.initializr.generator.InvalidProjectRequestException
@@ -36,12 +38,15 @@ abstract class AbstractInitializrController {
 
 	protected final InitializrMetadataProvider metadataProvider
 	private final GroovyTemplate groovyTemplate
+	private final Closure<String> linkTo
 	private Boolean forceSsl
 
 	protected AbstractInitializrController(InitializrMetadataProvider metadataProvider,
+										   ResourceUrlProvider resourceUrlProvider,
 										   GroovyTemplate groovyTemplate) {
 		this.metadataProvider = metadataProvider
 		this.groovyTemplate = groovyTemplate
+		this.linkTo = { link -> resourceUrlProvider.getForLookupPath(link)?:link }
 	}
 
 	boolean isForceSsl() {
@@ -79,6 +84,9 @@ abstract class AbstractInitializrController {
 		// Google analytics support
 		model['trackingCode'] = metadata.configuration.env.googleAnalyticsTrackingCode
 
+		// Linking to static resources
+		model['linkTo'] = this.linkTo
+
 		groovyTemplate.process templatePath, model
 	}
 

initializr-web/src/main/groovy/io/spring/initializr/web/project/LegacyStsController.groovy

@@ -22,6 +22,7 @@ import io.spring.initializr.util.GroovyTemplate
 import org.springframework.stereotype.Controller
 import org.springframework.web.bind.annotation.RequestMapping
 import org.springframework.web.bind.annotation.ResponseBody
+import org.springframework.web.servlet.resource.ResourceUrlProvider
 
 /**
  * A controller used to serve the legacy home page used by STS.
@@ -33,8 +34,9 @@ import org.springframework.web.bind.annotation.ResponseBody
 @Deprecated
 class LegacyStsController extends AbstractInitializrController {
 
-	LegacyStsController(InitializrMetadataProvider metadataProvider, GroovyTemplate groovyTemplate) {
-		super(metadataProvider, groovyTemplate)
+	LegacyStsController(InitializrMetadataProvider metadataProvider, ResourceUrlProvider resourceUrlProvider,
+						GroovyTemplate groovyTemplate) {
+		super(metadataProvider, resourceUrlProvider, groovyTemplate)
 	}
 
 	@RequestMapping(value = '/sts', produces = 'text/html')

initializr-web/src/main/groovy/io/spring/initializr/web/project/MainController.groovy

@@ -16,6 +16,8 @@
 
 package io.spring.initializr.web.project
 
+import org.springframework.web.servlet.resource.ResourceUrlProvider
+
 import java.nio.charset.StandardCharsets
 import java.util.concurrent.TimeUnit
 
@@ -74,8 +76,9 @@ class MainController extends AbstractInitializrController {
 	private final CommandLineHelpGenerator commandLineHelpGenerator
 
 	MainController(InitializrMetadataProvider metadataProvider, GroovyTemplate groovyTemplate,
-				   ProjectGenerator projectGenerator, DependencyMetadataProvider dependencyMetadataProvider) {
-		super(metadataProvider, groovyTemplate)
+				   ResourceUrlProvider resourceUrlProvider, ProjectGenerator projectGenerator,
+				   DependencyMetadataProvider dependencyMetadataProvider) {
+		super(metadataProvider, resourceUrlProvider, groovyTemplate)
 		this.projectGenerator = projectGenerator
 		this.dependencyMetadataProvider = dependencyMetadataProvider
 		this.commandLineHelpGenerator = new CommandLineHelpGenerator(groovyTemplate)

initializr-web/src/main/resources/templates/home.html

@@ -3,9 +3,9 @@
 <head>
     <title>Spring Initializr</title>
     <link href="//fonts.googleapis.com/css?family=Varela+Round|Montserrat:400,700" rel="stylesheet" type="text/css">
-    <link rel="stylesheet" href="/css/bootstrap.min.css"/>
-    <link rel="stylesheet" href="/css/bootstrap-theme.min.css"/>
-    <link rel="stylesheet" href="/css/spring.css"/>
+    <link rel="stylesheet" href="${linkTo.call('/css/bootstrap.min.css')}"/>
+    <link rel="stylesheet" href="${linkTo.call('/css/bootstrap-theme.min.css')}"/>
+    <link rel="stylesheet" href="${linkTo.call('/css/spring.css')}"/>
     <link rel="shortcut icon" type="image/x-icon" href="/img/favicon.png"/>
     <meta name="viewport" content="width=device-width, initial-scale=1">
 </head>
@@ -170,10 +170,10 @@
             and <a href="https://run.pivotal.io">Pivotal Web Services</a></p>
     </div>
 </footer>
-<script src="/js/jquery-3.1.1.min.js"></script>
-<script src="/js/typeahead.bundle.min.js"></script>
-<script src="/js/mousetrap.min.js"></script>
-<script src="/js/start.js"></script>
+<script src="${linkTo.call('/js/jquery-3.1.1.min.js')}"></script>
+<script src="${linkTo.call('/js/typeahead.bundle.min.js')}"></script>
+<script src="${linkTo.call('/js/mousetrap.min.js')}"></script>
+<script src="${linkTo.call('/js/start.js')}"></script>
 <% if (trackingCode) { %>
 <script>
     (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){