Java: Get Exchange Rate From Yahoo Finance Api

In this post, I will show you how to retrieve currency exchange rate from yahoo finance api by Java program.
There are some apis for getting exchange rate - reuters, bloomberg, yahoo finance etc.
If you don't have to get high-ratency realtime exchange rate, the most simple and free api - yahoo finance api - is enough.

Okay, here is the actual code. The api returns exchange rate as a Rate object.

package com.dukesoftware.exchangerate.api;

import static java.lang.String.format;

import java.io.ByteArrayOutputStream;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URI;


public class YahooExchangeRateApi implements ExchangeRateApi {
    
    // url for yahoo finance api
    private final static String URL_FORMAT = "http://finance.yahoo.com/d/quotes.csv?e=.csv&f=sl1d1t1&s=%s%s=X";
    
    
    public Rate getRate(String ccy1, String ccy2)
    {
        assertNotNull(ccy1, "Invalid ccy1" + ccy1);
        assertNotNull(ccy2, "Invalid ccy2" + ccy2);
        
        String urlStr = format(URL_FORMAT, ccy1, ccy2);
        
        HttpURLConnection connection = null;
        InputStream is = null;
        try
        {
            URI uri = new URI(urlStr);
            connection = (HttpURLConnection)uri.toURL().openConnection();
            connection.connect();
            is = connection.getInputStream();

            // raw return string is formatted as csv
            String content = toString(is);
            
            String[] data = content.split(",");
            
            Rate rate = new Rate();
            
            rate.setCcy1(ccy1);
            rate.setCcy2(ccy2);
            rate.setDate(data[2].replaceAll("\"", ""));
            rate.setValue(Double.parseDouble(data[1]));
            
            return rate;
        }
        catch(Exception e)
        {
            throw new IllegalStateException("fail to get rate for " + ccy1 + ccy2, e);
        }
        finally{
            closeQuietly(is);
            
            if(connection != null)
            {
                connection.disconnect();
            }
        }
    }

    // utility methods
    private static String toString(InputStream is) throws IOException
    {
        byte[] buf = new byte[1024];
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        for(int len = is.read(buf); len > 0; len = is.read(buf))
        {
            baos.write(buf, 0, len);
        }
        return baos.toString();
    }

    private static void assertNotNull(Object object, String message)
    {
        if(object == null)
        {
            throw new IllegalArgumentException(message);
        }
    }

    private static void closeQuietly(Closeable closeable)
    {
        if(closeable != null)
        {
            try {
                closeable.close();
            } catch (IOException e) {
            }
        }
        
    }
}

The below interface is a generic interface for getting exchange rate.

package com.dukesoftware.exchangerate.api;

public interface ExchangeRateApi {

    Rate getRate(String ccy1, String ccy2);
    
}

This is rate class.

package com.dukesoftware.exchangerate.api;

public class Rate {

    private String ccy1;
    private String ccy2;
    
    private Double value;
    private String date;

    public String getCcy1() {
        return ccy1;
    }
    public void setCcy1(String ccy1) {
        this.ccy1 = ccy1;
    }
    public String getCcy2() {
        return ccy2;
    }
    public void setCcy2(String ccy2) {
        this.ccy2 = ccy2;
    }
    public Double getValue() {
        return value;
    }
    public void setValue(Double value) {
        this.value = value;
    }
    public String getDate() {
        return date;
    }
    public void setDate(String date) {
        this.date = date;
    }
    
    @Override
    public String toString() {
        return "ccy1:"+ccy1+",ccy2:"+ccy2+",date:" + date + ",value:" + value;
    }
}