unable to find valid certification path to requested target - Only happening when trying to access XML file from Controller but not from normal class

I have a controller I am trying to access a Xml file to create an arraylist. But it throws the error in the title when trying to access the URL - this is strange because the code is working fine in a normal java class but only in my servlet this is happening.

Can anyone provide some help or advice ? Below is some of the code of the servlet:

@WebServlet

public class RSSController extends HttpServlet {

private static ArrayList<RSSFeed> list = new ArrayList<RSSFeed>();


public void service(HttpServletRequest req, HttpServletResponse res) throws IOException {
    String test = "TEST TEXT";

    PrintWriter out = res.getWriter();
    out.println(test);

    out.println("RSS Function: " + readRSSFeed("https://www.health.gov.au/news/rss.xml"));
    out.println(list.size());
    System.out.println("hi");
    for(int i = 0; i < list.size(); i++){

        RSSFeed temp = list.get(i);
        out.println(temp.getLink());
        out.println(temp.getTitle());
        out.println(i);
    }
}

public static String readRSSFeed(String urlAddress){
    System.out.println("readRSSFeed Function has started");
    try{
        System.out.println("Try loop has initated");
        URL rssUrl = new URL (urlAddress);
        BufferedReader in = new BufferedReader(new InputStreamReader(rssUrl.openStream()));
        String sourceCode = "";
        String line;
        while((line=in.readLine())!=null){

            if(line.contains("<title>")){
                System.out.println(line);
                int firstPos = line.indexOf("<title>");
                String temp = line.substring(firstPos);
                temp=temp.replace("<title>","");
                int lastPos = temp.indexOf("</title>");
                temp = temp.substring(0,lastPos);
                sourceCode +=temp+ "\n" ;

                RSSFeed tempRSS = new RSSFeed(temp, "testDesc", "testLink");
                list.add(tempRSS);
                System.out.println(tempRSS.getTitle());
            }
        }
        in.close();
        return sourceCode;
        //If URL does not work
    } catch (MalformedURLException ue){
        System.out.println("Malformed URL");
    } catch (IOException ioe){ //Any other issues
        System.out.println("Something went wrong reading the contents");
        ioe.printStackTrace();
    }
    return null;
}