Simple Currency Conversion using Google Calculator and Java

Here’s a little trick that I use to generate seed values for some of our mock components to ensure these values are fairly realistic.
Google has a web service that when queried returns a JSON string for calculated values. It’s basically a web service for the extremely useful Google Calculator.
If you point your browser to http://www.google.com/ig/calculator?hl=en&q=1GBP%3D%3FAUD you can see the result for yourself. I’ve wrapped this service in a small java class to demonstrate how to perform these types of calculations programmatically. The class makes use of GSON, which is another really useful Google API for converting JSON objects into POJOs.

package com.caplin.datasrc.ret.ct;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URL;
import com.google.gson.Gson;
public class SeedGenerator
{
	static class Result
    {
        private String lhs;
        private String rhs;
        public String getLhs()
        {
        	return lhs;
        }
        public String getRhs()
        {
        	return rhs;
        }
        public void setLhs(String lhs)
        {
        	this.lhs = lhs;
        }
        public void setRhs(String rhs)
        {
        	this.rhs = rhs;
        }
    }
	public static void main(String[] args) throws Exception
	{
	    String google = "http://www.google.com/ig/calculator?hl=en&q=";
	    String baseCurrency = "GBP";
	    String termCurrency = "AUD";
	    String charset = "UTF-8";
	    URL url = new URL(google + baseCurrency + "%3D%3F" + termCurrency);
	    Reader reader = new InputStreamReader(url.openStream(), charset);
	    Result result = new Gson().fromJson(reader, Result.class);
	    // Get the value without the term currency.
	    String amount = result.getRhs().split("\\s+")[0];
	    System.out.println(amount);
	}
}


The beauty of Google Calculator is of course that it can be used for any conversion. If you point your browser to http://www.google.com/ig/calculator?hl=en&q=1%20mile=?kilometer you will get the following result:

{lhs: "1 mile",rhs: "1.609344 kilometers",error: "",icc: false}

Even extremely arbitrary calculations work! For example http://www.google.com/ig/calculator?hl=en&q=furlongs%20in%20light%20year produces:

{lhs: "1 light year",rhs: "4.70279985 \x26#215; 10\x3csup\x3e13\x3c/sup\x3e furlongs",error: "",icc: false}

which looks like 4.70279985 × 1013. Pretty cool!

8 thoughts on “Simple Currency Conversion using Google Calculator and Java”

  1. Thanx really helpful.
    As i did experiments hope the url should be in this format
    “http://www.google.com/ig/calculator?hl=en&q=1GBP=?USD”
    isn’t that your code doesn’t add the initial amount to the url ? hope it have to be there just after “q=”.

  2. thanks for sharing
    run:
    Exception in thread “main” java.io.IOException: Server returned HTTP response code: 400 for URL: http://www.google.com/ig/calculator?hl=en&q=GBP%3D%3FUSD
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1436)
    at java.net.URL.openStream(URL.java:1010)
    at com.caplin.datasrc.ret.ct.SeedGenerator.main(SeedGenerator.java:52)
    Java Result: 1
    BUILD SUCCESSFUL (total time: 3 seconds)
    how to fix this ?
    —–

  3. Sorry, about my first post :
    i missed to say that when i run your program: in my netbeans developer
    i get the following lines:
    run:
    Exception in thread “main” java.io.IOException: Server returned HTTP response code: 400 for URL: http://www.google.com/ig/calculator?hl=en&q=GBP%3D%3FUSD
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1436)
    at java.net.URL.openStream(URL.java:1010)
    at com.caplin.datasrc.ret.ct.SeedGenerator.main(SeedGenerator.java:52)
    Java Result: 1
    BUILD SUCCESSFUL (total time: 3 seconds)
    how to fix this ?

  4. new Gson().fromJson(reader, Result.class)
    the above statement returned null, why pls help me
    Exception in thread “main” java.lang.NullPointerException
    at com.mm.CurrencyConverter.main(CurrencyConverter.java:42)

  5. hi
    i need api that create a table and update currency rates on daily bases in that table from which i will able to fetch required currency rate any time. currently i am using api that converts currency at real time and it is working fine but i need updated currency rates on daily bases in db table.
    thnx,

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