Add project request post processing

This commit introduces `ProjectRequestPostProcessor` as a mean to modify
an incoming `ProjectRequest` before and after its resolution against the
meta-data.

By default, all beans of that type are invoked automatically and they
are ordered against their `@Order` or `Ordered` settings.

Closes gh-260

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

@@ -20,6 +20,8 @@ import java.util.concurrent.TimeUnit
 
 import com.google.common.cache.CacheBuilder
 import io.spring.initializr.generator.ProjectGenerator
+import io.spring.initializr.generator.ProjectRequestPostProcessor
+import io.spring.initializr.generator.ProjectRequestResolver
 import io.spring.initializr.generator.ProjectResourceLocator
 import io.spring.initializr.metadata.DependencyMetadataProvider
 import io.spring.initializr.metadata.InitializrMetadataBuilder
@@ -30,6 +32,7 @@ import io.spring.initializr.web.support.DefaultDependencyMetadataProvider
 import io.spring.initializr.web.support.DefaultInitializrMetadataProvider
 import io.spring.initializr.web.ui.UiController
 
+import org.springframework.beans.factory.annotation.Autowired
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean
 import org.springframework.boot.context.properties.EnableConfigurationProperties
 import org.springframework.cache.CacheManager
@@ -56,6 +59,9 @@ import org.springframework.context.annotation.Configuration
 @EnableConfigurationProperties(InitializrProperties)
 class InitializrAutoConfiguration {
 
+	@Autowired(required = false)
+	List<ProjectRequestPostProcessor> postProcessors = []
+
 	@Bean
 	WebConfig webConfig() {
 		new WebConfig()
@@ -79,6 +85,12 @@ class InitializrAutoConfiguration {
 		new ProjectGenerator()
 	}
 
+	@Bean
+	@ConditionalOnMissingBean
+	ProjectRequestResolver projectRequestResolver() {
+		new ProjectRequestResolver(postProcessors)
+	}
+
 	@Bean
 	ProjectResourceLocator projectResourceLocator() {
 		return new ProjectResourceLocator()

initializr-web/src/test/groovy/io/spring/initializr/web/project/ProjectGenerationPostProcessorTests.groovy

@@ -0,0 +1,59 @@
+package io.spring.initializr.web.project
+
+import io.spring.initializr.generator.ProjectRequest
+import io.spring.initializr.generator.ProjectRequestPostProcessor
+import io.spring.initializr.generator.ProjectRequestPostProcessorAdapter
+import io.spring.initializr.metadata.InitializrMetadata
+import io.spring.initializr.web.AbstractInitializrControllerIntegrationTests
+import org.junit.Test
+
+import org.springframework.boot.test.SpringApplicationConfiguration
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+import org.springframework.core.annotation.Order
+import org.springframework.test.context.ActiveProfiles
+
+@ActiveProfiles('test-default')
+@SpringApplicationConfiguration(classes = [Config, ProjectRequestPostProcessorConfiguration])
+class ProjectGenerationPostProcessorTests extends AbstractInitializrControllerIntegrationTests {
+
+
+	@Test
+	void postProcessorsInvoked() {
+		downloadZip('/starter.zip?bootVersion=1.2.4.RELEASE&javaVersion=1.6')
+				.isJavaProject()
+				.isMavenProject().pomAssert()
+				.hasSpringBootParent('1.2.3.RELEASE')
+				.hasProperty('java.version', '1.7')
+	}
+
+
+	@Configuration
+	static class ProjectRequestPostProcessorConfiguration {
+
+		@Bean
+		@Order(2)
+		ProjectRequestPostProcessor secondPostProcessor() {
+			new ProjectRequestPostProcessorAdapter() {
+				@Override
+				void postProcessBeforeResolution(ProjectRequest request, InitializrMetadata metadata) {
+					request.javaVersion = '1.7'
+				}
+			}
+		}
+
+		@Bean
+		@Order(1)
+		ProjectRequestPostProcessor firstPostProcessor() {
+			new ProjectRequestPostProcessorAdapter() {
+				@Override
+				void postProcessBeforeResolution(ProjectRequest request, InitializrMetadata metadata) {
+					request.javaVersion = '1.2'
+					request.bootVersion = '1.2.3.RELEASE'
+				}
+			}
+		}
+
+	}
+
+}