BitfinexAPIServlet.java

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.conn.ssl.TrustStrategy;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.PoolingClientConnectionManager;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.security.KeyManagementException;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.UnrecoverableKeyException;
import java.util.Scanner;

public class BitfinexAPIServlet extends HttpServlet{
    private Exception exception;
    private String urlOverHttps = "https://api.bitfinex.com/v1/pubticker/btcusd";

    private double usdbtc;
    private long lastRespTime;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if (lastRespTime + 60 * 1000 < System.currentTimeMillis()) {
            try {
                usdbtc = requestUSDBTC();
            } catch (Exception e) {
                e.printStackTrace();
                exception = e;
            } finally {
                lastRespTime = System.currentTimeMillis();
            }
            exception = null;
        }

        ObjectMapper mapper = new ObjectMapper();
        ObjectNode node = mapper.createObjectNode();
        node.put("last_price", usdbtc);
        node.put("error", exception != null);

        final Object obj = mapper.treeToValue(node, Object.class);
        final String json = mapper.writeValueAsString(obj);

        resp.getWriter().print(json);
        resp.setStatus(HttpServletResponse.SC_OK);
    }

    public double requestUSDBTC() throws IOException, UnrecoverableKeyException, NoSuchAlgorithmException, KeyStoreException, KeyManagementException {
        TrustStrategy acceptingTrustStrategy = (cert, authType) -> true;
        SSLSocketFactory sf = new SSLSocketFactory(
                acceptingTrustStrategy, SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER);
        SchemeRegistry registry = new SchemeRegistry();
        registry.register(new Scheme("https", 8443, sf));
        ClientConnectionManager ccm = new PoolingClientConnectionManager(registry);

        DefaultHttpClient httpClient = new DefaultHttpClient(ccm);

        HttpGet getMethod = new HttpGet(urlOverHttps);

        HttpResponse response = httpClient.execute(getMethod);

        String result;
        try(Scanner s = new Scanner(response.getEntity().getContent()).useDelimiter("\\A")) {
            result = s.hasNext() ? s.next() : "";
        }

        ObjectMapper objectMapper = new ObjectMapper();
        JsonNode jsonNode = objectMapper.readTree(result);

        return jsonNode.get("last_price").asDouble();
    }
}