diff --git a/extensions/database/pom.xml b/extensions/database/pom.xml
index 709dbfab3..3ce14a65c 100644
--- a/extensions/database/pom.xml
+++ b/extensions/database/pom.xml
@@ -27,7 +27,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -45,10 +45,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/extensions/gdata/pom.xml b/extensions/gdata/pom.xml
index 9a0ef3c64..192746425 100644
--- a/extensions/gdata/pom.xml
+++ b/extensions/gdata/pom.xml
@@ -27,7 +27,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -45,10 +45,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/extensions/jython/pom.xml b/extensions/jython/pom.xml
index 1399693fa..c095b60f2 100644
--- a/extensions/jython/pom.xml
+++ b/extensions/jython/pom.xml
@@ -29,7 +29,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -47,10 +47,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/extensions/pc-axis/pom.xml b/extensions/pc-axis/pom.xml
index 90d01ce27..c38a34578 100644
--- a/extensions/pc-axis/pom.xml
+++ b/extensions/pc-axis/pom.xml
@@ -27,7 +27,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -45,10 +45,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/extensions/phonetic/pom.xml b/extensions/phonetic/pom.xml
index f7c3a5a74..851eb6bb5 100644
--- a/extensions/phonetic/pom.xml
+++ b/extensions/phonetic/pom.xml
@@ -29,7 +29,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -47,10 +47,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/extensions/sample/pom.xml b/extensions/sample/pom.xml
index 1b2dd8145..78ab96db1 100644
--- a/extensions/sample/pom.xml
+++ b/extensions/sample/pom.xml
@@ -28,7 +28,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -46,10 +46,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/extensions/wikidata/pom.xml b/extensions/wikidata/pom.xml
index 90e487b17..96e10e84c 100644
--- a/extensions/wikidata/pom.xml
+++ b/extensions/wikidata/pom.xml
@@ -37,7 +37,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -55,10 +55,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/main/pom.xml b/main/pom.xml
index 2969d8f6b..e0e2eddc0 100644
--- a/main/pom.xml
+++ b/main/pom.xml
@@ -44,7 +44,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -62,9 +62,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.8.0</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-	  <!--release>11</release-->
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>
diff --git a/pom.xml b/pom.xml
index c9107b449..e1d0cd6ab 100644
--- a/pom.xml
+++ b/pom.xml
@@ -56,6 +56,9 @@
     <jee.path>/</jee.path>
     <jee.port>3333</jee.port>
     <refine.data>/tmp/refine</refine.data>
+    <maven-compiler-plugin.release>9</maven-compiler-plugin.release>  <!-- Which Java version to cross-compile against -->  
+    <maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
+    <build-helper-maven-plugin.version>3.1.0</build-helper-maven-plugin.version>
     <surefire.version>2.22.2</surefire.version>
     <surefireArgs></surefireArgs>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
@@ -74,7 +77,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -92,11 +95,11 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
+          <showWarnings>true</showWarnings>
           <showDeprecation>false</showDeprecation>
         </configuration>
       </plugin>
diff --git a/server/pom.xml b/server/pom.xml
index 17ce539a7..5132b26ec 100644
--- a/server/pom.xml
+++ b/server/pom.xml
@@ -37,7 +37,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>
-        <version>1.8</version>
+        <version>${build-helper-maven-plugin.version}</version>
         <executions>
           <execution>
             <phase>generate-sources</phase>
@@ -55,10 +55,9 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.1</version>
+        <version>${maven-compiler-plugin.version}</version>
         <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
+          <release>${maven-compiler-plugin.release}</release>
           <encoding>UTF-8</encoding>
           <showDeprecation>false</showDeprecation>
         </configuration>