Functional Programming in Java, Second Edition: p.91: Rewrite FinanceData HTTP request method

dtonhofer · 2023-04-21T14:26:37.194Z

On page 91, we use a short method to request a stock ticker, class FinanceData

However, this method is based on java.net.URL which has always been broken in several ways, one which being that it doesn’t encode the URL itself. That class is also deprecated in Java 20. The replacement is java.net.URI (since Java 7).

The construction of the query string, while appropriate as an exercise, can also be done better while demonstrating stream use.

Anyway, let’s go. Here is a definitely longer but IMHO nicer replacement:

    public class FinanceData {
        public static BigDecimal getPrice(final String ticker) {
            HttpResponse<String> response;
            try {
                final String scheme = "https";
                final String authority = "eodhistoricaldata.com";
                final String path = String.format("/api/eod/%s.US",ticker);
                final String query =
                        List.of("fmt=json", "filter=last_close", "api_token=OeAFFmMliFG5orCUuwAKQ8l4WWFQ67YX")
                                .stream()
                                .collect(Collectors.joining("&"));
                final String fragment = null;
                final URI uri = new URI(scheme,authority,path,query,fragment);
                System.out.println("Connecting to URI: " + uri);
                HttpClient client = HttpClient.newHttpClient();
                HttpRequest request = HttpRequest.newBuilder().uri(uri).build();
                response = client.send(request, HttpResponse.BodyHandlers.ofString(StandardCharsets.UTF_8));
            } catch(Exception ex) {
                throw new RuntimeException(ex);
            }
            System.out.println("Received status code: " + response.statusCode());
            if (response.statusCode() == 200) {
                System.out.println("Received body: " + response.body());
                // parsing BigDecimal will throw on bad syntax
                return new BigDecimal(response.body());
            }
            else {
                throw new IllegalStateException("Status code was: " + response.statusCode());
            }
        }
    }

venkats · 2023-05-31T19:33:55.560Z

Decided to keep the change minimum here and resolve the deprecation warning. Fixed. Thank you.

dtonhofer · 2023-06-02T08:36:44.202Z

Thank you.

That’s a damn shame (let’s just say I remember having to direct my companion devs forcefully away from using URL back in the early 00’s I think in the end we went with the Apache HttpClient …)

venkats · 2023-06-02T09:14:13.013Z

Practically, given the context of this example code, there is little benefit to the reader to see more code than minimally necessary for this function.