CurrencyCalculator.java

package exchangerate;

import java.util.HashMap;

/**
 *
 * @author sachithra
 */
public class CurrencyCalculator {

    private HashMap<String, Double> rates;
    private String base;

    public CurrencyCalculator() {
        this.rates = new HashMap();
        this.rates.put("USD", 1.0);
        this.rates.put("EUR", 0.933);
        this.rates.put("LKR", 149.132);
        this.rates.put("AUD", 1.345);
        this.rates.put("YEN", 114.123);
        this.base = "USD";
    }

    public double getExchangeRate(String from, String to) {
        if (rates.containsKey(from) && rates.containsKey(to)) {
            double toVal = rates.get(to);
            double fromVal = rates.get(from);
            double rate = toVal / fromVal;
            return rate;
        }
        return 0;
    }
}

ExchangeRate.java

package exchangerate;

import javax.ws.rs.core.Context;
import javax.ws.rs.core.UriInfo;
import javax.ws.rs.Consumes;
import javax.ws.rs.Produces;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PUT;
import javax.ws.rs.PathParam;
import javax.ws.rs.core.MediaType;

/**
 * REST Web Service
 *
 * @author sachithra
 */
@Path("rates")
public class ExchangeRate {

    @Context
    private UriInfo context;

    private final CurrencyCalculator rates;

    /**
     * Creates a new instance of ExchangeRate
     */
    public ExchangeRate() {
        rates = new CurrencyCalculator();
    }

    /**
     * Retrieves representation of an instance of exchangerate.ExchangeRate
     *
     * @param from
     * @param to
     * @return an instance of java.lang.String
     */
    @GET
    @Path("{from}/{to}")
    @Produces(MediaType.TEXT_PLAIN)
    public String getRates(@PathParam("from") String from, @PathParam("to") String to) {
        double value = rates.getExchangeRate(from, to);
        String resultText = "";
        if(value!=0){
             resultText = "1 " + from + " is equal to " + value + " " + to;
        }else{
            resultText = "Sorry, the currencies you defined are invalid or not yet implemented.";
        }
        return resultText;
    }

    /**
     * PUT method for updating or creating an instance of ExchangeRate
     *
     * @param content representation for the resource
     */
    @PUT
    @Consumes(MediaType.TEXT_PLAIN)
    public void putText(String content) {
    }
}