Issue #487 - JDK 9 build compatibility.

Made sure that when compiling with JDK 9 we actually use a JDK 8 runtime.

Updated the Maven Compiler Plugin to latest version, with support for
JDK 9 --release command line.

Removed unnecessary Maven Compiler Plugin declarations in POMs.

aggregates/jetty-all-compact3/pom.xml

@@ -20,8 +20,6 @@
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
         <configuration>
-          <source>8</source>
-          <target>8</target>
           <compilerArgs>
             <arg>-profile</arg>
             <arg>compact3</arg>

jetty-alpn/jetty-alpn-java-client/pom.xml

@@ -24,6 +24,7 @@
                 <configuration>
                     <source>1.9</source>
                     <target>1.9</target>
+                    <release>9</release>
                 </configuration>
             </plugin>
         </plugins>

jetty-alpn/jetty-alpn-java-server/pom.xml

@@ -23,6 +23,7 @@
                 <configuration>
                     <source>1.9</source>
                     <target>1.9</target>
+                    <release>9</release>
                 </configuration>
             </plugin>
         </plugins>

jetty-osgi/test-jetty-osgi/pom.xml

@@ -390,15 +390,6 @@
           <argLine>-Dmortbay-alpn-boot=${settings.localRepository}/org/mortbay/jetty/alpn/alpn-boot/${alpn.version}/alpn-boot-${alpn.version}.jar</argLine>
         </configuration>
       </plugin>
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-compiler-plugin</artifactId>
-        <version>2.5.1</version>
-        <configuration>
-          <source>1.7</source>
-          <target>1.7</target>
-        </configuration>
-      </plugin>
       <plugin>
         <groupId>org.apache.servicemix.tooling</groupId>
         <artifactId>depends-maven-plugin</artifactId>

pom.xml

@@ -35,17 +35,6 @@
   <build>
     <defaultGoal>install</defaultGoal>
     <plugins>
-      <plugin>
-        <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.3</version>
-        <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
-          <testSource>1.8</testSource>
-          <testTarget>1.8</testTarget>
-          <verbose>false</verbose>
-        </configuration>
-      </plugin>
       <plugin>
         <artifactId>maven-release-plugin</artifactId>
         <version>2.5</version>
@@ -333,6 +322,15 @@
             </dependency>
           </dependencies>
         </plugin>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <version>3.6.2</version>
+          <configuration>
+            <source>1.8</source>
+            <target>1.8</target>
+          </configuration>
+        </plugin>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-dependency-plugin</artifactId>
@@ -802,17 +800,6 @@
       <modules>
         <module>aggregates/jetty-all</module>
       </modules>
-      <build>
-        <plugins>
-          <plugin>
-            <artifactId>maven-compiler-plugin</artifactId>
-            <configuration>
-              <source>1.8</source>
-              <target>1.8</target>
-            </configuration>
-          </plugin>
-        </plugins>
-      </build>
     </profile>
     <profile>
       <id>ci</id>
@@ -1256,5 +1243,21 @@
         <alpn.version>8.1.11.v20170118</alpn.version>
       </properties>
     </profile>
+    <profile>
+      <id>jdk9</id>
+      <activation>
+        <jdk>[1.9,)</jdk>
+      </activation>
+      <build>
+        <plugins>
+          <plugin>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <configuration>
+              <release>8</release>
+            </configuration>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
   </profiles>
 </project>

tests/test-webapps/test-mock-resources/pom.xml

@@ -13,12 +13,6 @@
   </properties>
   <build>
     <plugins>
-      <plugin>
-        <artifactId>maven-compiler-plugin</artifactId>
-        <configuration>
-          <verbose>false</verbose>
-        </configuration>
-      </plugin>
       <plugin>
         <groupId>org.apache.felix</groupId>
         <artifactId>maven-bundle-plugin</artifactId>

tests/test-webapps/test-servlet-spec/test-container-initializer/pom.xml

@@ -13,12 +13,6 @@
   </properties>
   <build>
     <plugins>
-       <plugin>
-        <artifactId>maven-compiler-plugin</artifactId>
-        <configuration>
-          <verbose>false</verbose>
-        </configuration>
-       </plugin>
        <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-jar-plugin</artifactId>

tests/test-webapps/test-servlet-spec/test-web-fragment/pom.xml

@@ -5,23 +5,15 @@
     <artifactId>test-servlet-spec-parent</artifactId>
     <version>9.3.22-SNAPSHOT</version>
   </parent>
+
   <name>Jetty Tests :: WebApp :: Servlet Spec :: Fragment Jar</name>
-  <groupId>org.eclipse.jetty.tests</groupId>
   <artifactId>test-web-fragment</artifactId>
   <packaging>jar</packaging>
+
   <properties>
     <bundle-symbolic-name>${project.groupId}.fragment</bundle-symbolic-name>
   </properties>
-  <build>
-    <plugins>
-      <plugin>
-        <artifactId>maven-compiler-plugin</artifactId>
-        <configuration>
-          <verbose>false</verbose>
-        </configuration>
-      </plugin>
-    </plugins>
-  </build>
+
   <dependencies>
       <dependency>
          <groupId>javax.servlet</groupId>