Spin out branches for JDK7 and JDK9 compatibility testing

Author: R. Tyler Croy

Jenkinsfile

@@ -5,21 +5,25 @@ node {
     checkout scm
 
     stage 'Build and test'
+    List<String> javas = ['7', '8']
     List<String> plugins = ['base', 'war', 'jar']
     Map parallelSteps = [:]
 
-    for (int i = 0; i < plugins.size(); i++) {
-        def plugin = "jruby-gradle-${plugins.get(i)}-plugin"
-        parallelSteps[plugin] = {
-            node('docker') {
-                checkout scm
-                docker.image('java:8-jdk').inside {
-                    timeout(30) {
-                        sh "./gradlew -Si ${plugin}:check ${plugin}:gradleTest ${plugin}:assemble"
+    for (int j = 0; j < javas.size(); j++) {
+        for (int i = 0; i < plugins.size(); i++) {
+            def javaVersion = "${javas.get(j)}-jdk"
+            def plugin = "jruby-gradle-${plugins.get(i)}-plugin"
+            parallelSteps["${javaVersion}-${plugin}"] = {
+                node('docker') {
+                    checkout scm
+                    docker.image("java:${javaVersion}").inside {
+                        timeout(30) {
+                            sh "./gradlew -Si ${plugin}:check ${plugin}:gradleTest ${plugin}:assemble"
+                        }
                     }
+                    junit 'build/test-results/**/*.xml'
+                    archiveArtifacts artifacts: 'build/libs/*.jar,build/*.zip', fingerprint: true
                 }
-                junit 'build/test-results/**/*.xml'
-                archiveArtifacts artifacts: 'build/libs/*.jar,build/*.zip', fingerprint: true
             }
         }
     }