Add Java test

tests/apps/java/src/main/java/HelloWorld.java

@@ -0,0 +1,22 @@
+import java.io.IOException;
+import javax.servlet.ServletException;
+import javax.servlet.http.*;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.servlet.*;
+
+public class HelloWorld extends HttpServlet {
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
+            throws ServletException, IOException {
+        resp.getWriter().print("Hello from Java!\n");
+    }
+    public static void main(String[] args) throws Exception{
+        Server server = new Server(Integer.valueOf(System.getenv("PORT")));
+        ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
+        context.setContextPath("/");
+        server.setHandler(context);
+        context.addServlet(new ServletHolder(new HelloWorld()),"/*");
+        server.start();
+        server.join();
+    }
+}