Improve your REST Webservice response time using java.util.TimerTask

A while ago, I built an MAF application, which was consuming a few REST webservices from Oracle Java Cloud. But for each request from the app, the response JSON was getting created, and which made the app response very slow. 
So, I created the contents of the REST response as a scheduled job. My data wasn't getting changed that often, so I choose to build my REST responses every morning at 10am using java.util.TimerTask.

Used Software: JDeveloper 12.1.3

#1. REST response POJOs :
public class Feed {
   
    public String url;
    public String source;
   
    public Feed() {
        super();
    }
   
    public Feed(String source, String url) {
        setSource(source);
        setUrl(url);
    }
   
    public void setSource(String source) {
        this.source = source;
    }

    public String getSource() {
        return source;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getUrl() {
        return url;
    }
}

================================

@XmlRootElement(name = "feeds")
public class FeedsArray {

    private List<Feed> feeds;

    public void setFeeds(List<Feed> feeds) {
        this.feeds = feeds;
    }

    public List<Feed> getFeeds() {
        return feeds;
    }
}

#2. TimerTask class :
You need to create a class which extends java.util.TimerTask and override run() to put your custom code.
I have used a Singleton object (Feeds) to create and store my response.

public class FeedRSSScheduler extends TimerTask {
    public FeedRSSScheduler() {
        super();
    }

    @Override
    public void run() {
        Feeds.getInstance().buildFeedsMap();
    }
}

============================

public class Feeds {
   
    private static Feeds instance = null;
   
    private FeedsArray feedsArray;
   
    protected Feeds() {
        super();
    }
   
    public static Feeds getInstance() {
      if(instance == null) {
         instance = new Feeds();
      }
      return instance;
    }


    public FeedsArray getFeedsArray() {
        if(feedsArray == null) {
            buildFeedsMap();
        }
        return feedsArray;
    }
   
    public void buildFeedsMap() {
        // PUT your custom code here to populate the FeedsArray object
    }
}

#3. Servlet container class :
 
public class JobSchedulerServlet extends ServletContainer {
   
    private final static long ONCE_PER_DAY = 1000*60*60*24;
    private final static int TEN_AM = 10;
    private final static int ZERO_MINUTES = 0;
   
    public JobSchedulerServlet(Application application) {
        super(application);
    }

    @Override
    public void init() throws ServletException {   
        startFeedRSSTask();
        super.init();
    }

    public JobSchedulerServlet(Class<? extends Application> class1) {
        super(class1);
    }

    public JobSchedulerServlet() {
        super();
    }
   
    private Date getTomorrowMorning10AM(){
        Date date2am = new Date();
        date2am.setHours(TEN_AM);
        date2am.setMinutes(ZERO_MINUTES);
        return date2am;
    }
   
    private void startFeedRSSTask(){
        FeedRSSScheduler feedRSSScheduler = new FeedRSSScheduler();
        Timer timer = new Timer(); 
        timer.schedule(feedRSSScheduler, getTomorrowMorning10AM(), ONCE_PER_DAY);
    }
}

#4. Register your Servlet container class in web.xml :
  <servlet>
    <servlet-name>jersey</servlet-name>
    <servlet-class>rest.scheduler.JobSchedulerServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>jersey</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>

#5. Create REST service :

@Path("/feeds")
public class FeedMap {
   
    @GET
    @Path("/sources")
    @Produces(MediaType.APPLICATION_JSON)
    public FeedsArray getFeedsMap() {
        return Feeds.getInstance().getFeedsArray();
    }
}
/// URL to access this service : http://<server>:<port>/<context_root>/feeds/sources

That's it. When you create and deploy this WAR file, the job will start instantly and then every day morning at 10am.