Adding files for BAEL-2196 (#6477)

* Adding files for BAEL-2196

* modified Package structure

maven/compiler-plugin-java-9/src/main/java/com/baeldung/maven/java9/MavenCompilerPlugin.java

@@ -0,0 +1,9 @@
+package com.baeldung.maven.java9;
+
+import static javax.xml.XMLConstants.XML_NS_PREFIX;
+
+public class MavenCompilerPlugin {
+    public static void main(String[] args) {
+        System.out.println("The XML namespace prefix is: " + XML_NS_PREFIX);
+    }
+}

maven/compiler-plugin-java-9/src/main/java/module-info.java

@@ -0,0 +1,3 @@
+module com.baeldung.maven.java9 {
+    requires java.xml;
+}