调用外部API并解析JSON对象

Question

I am trying to fetch JSON from external API and parse it so that I can access JSON object values in order to avoid values(fields) that I do not need.

I have studied JSONOBject library a little and parsed the objects, however, it feels that I am doing too much hard coding and not doing it correctly at all, feedback is much appreciated.

Output result after user input :

Sending 'GET' request to URL: https://api.coindesk.com/v1/bpi/currentprice/(user input currency)

Data fetched at UTC time/date : Sep 17, 2019 22:51:00 UTC Description: Ukrainian Hryvnia Rate float: 253737.6633

import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class App {

    public static void main(String[] args) throws IOException {

        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

        System.out.println("Please enter the currency you would like to get BTC current rate for");
        String userInput = in.readLine();


        try {

            String url = "https://api.coindesk.com/v1/bpi/currentprice/" + userInput;
            URL obj = new URL(url);

            // HttpURLConnection instance is making a request
            //openConnection() method of URL class opens the connection to specified URL
            HttpURLConnection con = (HttpURLConnection) obj.openConnection();

            // saving the response code from the request
            int responseCode = con.getResponseCode();

            System.out.println("\nSending 'GET' request to URL : " + url);
            System.out.println("---------------------------------------------");
            System.out.println("Response Code from the HTTP request : " + responseCode);
            System.out.println("---------------------------------------------");

            //creating reader instance to reade the response from the HTTP GET request
            BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream()));

            String userInputLine;
            StringBuilder response = new StringBuilder();

            //if there is still something to read from -> then read and append to String builder -> can be mutable
            while ((userInputLine = reader.readLine()) != null) {
                response.append(userInputLine);
            }

            //closing reader
            reader.close();

            //Converting response to JSON object
            JSONObject myresponse = new JSONObject(response.toString());


            JSONObject bpiObject = new JSONObject(myresponse.getJSONObject("bpi").toString());
            JSONObject currencyObjects = new JSONObject(bpiObject.getJSONObject(userInput).toString());

            // since response got a objects within objects, we need to dig dipper in order to access field values
            JSONObject timeObject = new JSONObject(myresponse.getJSONObject("time").toString());
            System.out.println("Data fetched at UTC time/date : " + timeObject.getString("updated"));

            System.out.println("Description : " + currencyObjects.getString("description") + "\nRate float : " + currencyObjects.getString("rate_float"));


        } catch (Exception e) {
            System.out.println(e);

        }

    }
}

Answer 1

I wrote a sample code to demonstrate what I said in comment by using ObjectMapper to transform response json string into POJO.

First, create a class, says CoinDeskResponse to store the transformation result.

public class CoinDeskResponse {
    private TimeInfo time;
    private String disclaimer;
    private BpiInfo bpi;
    //general getters and setters
}

class TimeInfo {
    private String updated;
    private String updatedISO;
    //general getters and setters
}

class BpiInfo {
    private String code;
    private String symbol;
    private String rate;
    private String description;

    @JsonProperty("rate_float")
    private String rateFloat;
    //general getters and setters
}

Next, create ObjectMapper and convert the response to CoinDeskResponse POJO. Then you can get desired data by manipulating the object.

    String responseStr = "{\"time\":{\"updated\":\"Sep 18, 2013 17:27:00 UTC\",\"updatedISO\":\"2013-09-18T17:27:00+00:00\"},\"disclaimer\":\"This data was produced from the CoinDesk Bitcoin Price Index. Non-USD currency data converted using hourly conversion rate from openexchangerates.org\",\"bpi\":{\"code\":\"USD\",\"symbol\":\"$\",\"rate\":\"126.5235\",\"description\":\"United States Dollar\",\"rate_float\":126.5235}}";
    ObjectMapper mapper = new ObjectMapper();
    try {
        CoinDeskResponse coinDeskResponse = mapper.readValue(responseStr, CoinDeskResponse.class);

        System.out.println(coinDeskResponse.getTime().getUpdated());
        System.out.println(coinDeskResponse.getBpi().getDescription());
        System.out.println(coinDeskResponse.getBpi().getRateFloat());
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Console output:

Data fetched at UTC time/date : Sep 18, 2013 17:27:00 UTC
Description : United States Dollar
Rate float : 126.5235