We have a web application which talks to spark server.
This is how we have done the integration.
1) In the tomcat's classpath, add the spark distribution jar for spark code to be available at runtime ( for you it would be Jetty).
2) In the Web application project, add the spark distribution jar in the classpath ( Could be Java / Web project).
3) Setup the FAIR scheduling mode, which would help send parallel requests from web application to the spark cluster.
4) In our application startup, initialize the connection to the spark cluster. This is composed of creating the JavaSparkContext and making it available throughout the web application, in case this needs to be the only Driver Program required by the web application.
5) Using the JavaSpark Context, Create RDD's and make them available globally to the web application code.
6) invoke transformation / actions as required.