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The RSS reader tutorial. Step 2.

Quick recap

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

The RSS reader example assumes implementing 3 endpoints. This article is dedicated to implementing the GET /user/{user_id}/rss_channels endpoint.

Before completing this step, make sure your are in the step_2 git branch:

git checkout step_2

Implementing the second endpoint

The second endpoint produces an array of RSS channels by given user_id.

We need to execute the two following queries to:

  1. Fetch RSS links for a given user:
    SELECT rss_link FROM rss_by_user WHERE login = GIVEN_USER_ID ;
  2. Fetch RSS channel details for a given link:
    SELECT description, title, site_link, rss_link FROM channel_info_by_rss_link WHERE rss_link = GIVEN_LINK ;


The endpoint allows the the front-end app to display the list of RSS feeds a user subscribed on. When the endpoint is accessed, the AppVerticle#getRssChannels method is called. We can implement this method in this way:

private void getRssChannels(RoutingContext ctx) {
    String userId = ctx.request().getParam("user_id");
    if (userId == null) {
    } else {
        Future<List<Row>> future = Future.future();
        client.executeWithFullFetch(selectRssLinksByLogin.bind(userId), future);
        future.compose(rows -> {
            List<String> links =
                    .map(row -> row.getString(0))

            return CompositeFuture.all(
           -> {
                        Future<List<Row>> channelInfoRow = Future.future();
                        client.executeWithFullFetch(statement, channelInfoRow);
                        return channelInfoRow;
        }).setHandler(h -> {
            if (h.succeeded()) {
                CompositeFuture result = h.result();
                List<List<Row>> results = result.list();
                List<Row> list =
                JsonObject responseJson = new JsonObject();
                JsonArray channels = new JsonArray();

                list.forEach(eachRow -> channels.add(
                        new JsonObject()
                                .put("description", eachRow.getString(0))
                                .put("title", eachRow.getString(1))
                                .put("link", eachRow.getString(2))
                                .put("rss_link", eachRow.getString(3))

                responseJson.put("channels", channels);
            } else {
                log.error("failed to get rss channels", h.cause());
                ctx.response().setStatusCode(500).end("Unable to retrieve the info from C*");

Also, this method uses selectChannelInfo and selectRssLinksByLogin fields, they should be initialized in the AppVerticle#prepareNecessaryQueries method:

private Future<Void> prepareNecessaryQueries() {
        Future<PreparedStatement> selectChannelInfoPrepFuture = Future.future();
        client.prepare("SELECT description, title, site_link, rss_link FROM channel_info_by_rss_link WHERE rss_link = ? ;", selectChannelInfoPrepFuture);

        Future<PreparedStatement> selectRssLinkByLoginPrepFuture = Future.future();
        client.prepare("SELECT rss_link FROM rss_by_user WHERE login = ? ;", selectRssLinkByLoginPrepFuture);

        Future<PreparedStatement> insertNewLinkForUserPrepFuture = Future.future();
        client.prepare("INSERT INTO rss_by_user (login , rss_link ) VALUES ( ?, ?);", insertNewLinkForUserPrepFuture);

        return CompositeFuture.all(
                selectChannelInfoPrepFuture.compose(preparedStatement -> {
                    selectChannelInfo = preparedStatement;
                    return Future.succeededFuture();
                selectRssLinkByLoginPrepFuture.compose(preparedStatement -> {
                    selectRssLinksByLogin = preparedStatement;
                    return Future.succeededFuture();
                insertNewLinkForUserPrepFuture.compose(preparedStatement -> {
                    insertNewLinkForUser = preparedStatement;
                    return Future.succeededFuture();


In this part, we have successfully implemented the second endpoint, which allows the browser app to obtain channels information for a specific user. To ensure that it is working fine, point your browser to localhost:8080 and click to the refresh button. Channel list should appear immediately.

If you have any problems with completing this step you can checkout to step_3, where you can find all changes made for completing this step:

git checkout step_3

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