The RSS reader tutorial (Step 3)

Now that Vert.x 3.6.0 has been re­leased, it’s the per­fect time to con­clude our Vert.x Cas­san­dra Client tu­to­r­ial!

In the pre­vi­ous step, we have suc­cess­fully im­ple­mented the sec­ond end­point of the RSS reader app.

The RSS reader ex­am­ple as­sumes im­ple­ment­ing three end­points. This ar­ti­cle is ded­i­cated to im­ple­ment­ing the last GET /articles/by_rss_link?link={rss_link} end­point.

Be­fore com­plet­ing this step, make sure your are in the step_3 git branch:

$ git checkout step_3

Implementing the 3rd endpoint

The 3rd end­point serves a list of ar­ti­cles re­lated to a spe­cific RSS chan­nel. In a re­quest, we spec­ify RSS chan­nel by pro­vid­ing a link. On the ap­pli­ca­tion side, after re­ceiv­ing a re­quest we ex­e­cute the fol­low­ing query:

SELECT title, article_link, description, pubDate FROM articles_by_rss_link WHERE rss_link = RSS_LINK_FROM_REQUEST ;

Implementation

For ob­tain­ing ar­ti­cles by RSS link we need to pre­pare a re­lated state­ment first. Change AppVerticle#prepareSelectArticlesByRssLink in this way:

private Future<Void> prepareSelectArticlesByRssLink() {
    return Util.prepareQueryAndSetReference(client,
            "SELECT title, article_link, description, pubDate FROM articles_by_rss_link WHERE rss_link = ? ;",
            selectArticlesByRssLink
    );
}

And now, we can im­ple­ment the AppVerticle#getArticles method. Ba­si­cally, it will use the selectArticlesByRssLink state­ment for find­ing ar­ti­cles by the given link. Here’s the im­ple­men­ta­tion:

private void getArticles(RoutingContext ctx) {
    String link = ctx.request().getParam("link");
    if (link == null) {
        responseWithInvalidRequest(ctx);
    } else {
        client.executeWithFullFetch(selectArticlesByRssLink.bind(link), handler -> {
            if (handler.succeeded()) {
                List<Row> rows = handler.result();

                JsonObject responseJson = new JsonObject();
                JsonArray articles = new JsonArray();

                rows.forEach(eachRow -> articles.add(
                        new JsonObject()
                                .put("title", eachRow.getString(0))
                                .put("link", eachRow.getString(1))
                                .put("description", eachRow.getString(2))
                                .put("pub_date", eachRow.getTimestamp(3).getTime())
                ));

                responseJson.put("articles", articles);
                ctx.response().end(responseJson.toString());
            } else {
                log.error("failed to get articles for " + link, handler.cause());
                ctx.response().setStatusCode(500).end("Unable to retrieve the info from C*");
            }
        });
    }
}

Conclusion

Dur­ing the se­ries, we have shown how the RSS reader app can be im­ple­mented with the Vert.x Cas­san­dra client.

Thanks for read­ing this. I hope you en­joyed this se­ries. See you soon on our Git­ter chan­nel!