gistfile1.txt

import com.mongodb.*;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.ws.Endpoint;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.StringJoiner;


public class Get extends javax.servlet.http.HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("Content-Type", "application/json");
        PrintWriter writer = resp.getWriter();

        MongoClient mongoClient = new MongoClient("localhost", 27017);
        DB db = mongoClient.getDB("mydb");
        DBCollection supplements = db.getCollection("supplements");
        DBCollection supplementPrices = db.getCollection("supplement_prices");


        try (DBCursor cursor = supplements.find()) {
            cursor.batchSize(2);
            StringJoiner sj = new StringJoiner(",", "[", "]");
            while (cursor.hasNext()) {
                DBObject dbObject = cursor.next();
                System.out.println(dbObject);
                Object priceId = dbObject.get("price_id");

                BasicDBObject query = new BasicDBObject("id", new BasicDBObject("$eq", String.valueOf(priceId)));
                DBObject priceObject = supplementPrices.findOne(query);
                System.out.println(priceObject);
                String x = dbObject.toString();
//                System.out.println(x + " = " + priceObject.toString());
                sj.add(x);
            }
            writer.write(sj.toString());
        }
        writer.flush();
        writer.close();
    }

}

//data

> db.supplements.find()
{ "_id" : ObjectId("54576ae0ac8d18d02b146498"), "name" : "Arden Grange", "weight" : "1kg", "price_id" : "10" }
{ "_id" : ObjectId("54576ae3ac8d18d02b146499"), "name" : "Arden Grange", "weight" : "2kg", "price_id" : "20" }
{ "_id" : ObjectId("54576ae5ac8d18d02b14649a"), "name" : "Arden Grange", "weight" : "3kg", "price_id" : "30" }
{ "_id" : ObjectId("54576aeaac8d18d02b14649b"), "name" : "Arden Grange", "weight" : "5kg", "price_id" : "40" }
{ "_id" : ObjectId("54576b26ac8d18d02b14649c"), "name" : "BLUE", "weight" : "5kg", "price_id" : "20" }
{ "_id" : ObjectId("54576b29ac8d18d02b14649d"), "name" : "BLUE", "weight" : "10kg", "price_id" : "50" }
{ "_id" : ObjectId("54576b3fac8d18d02b14649e"), "name" : "Chappie", "weight" : "100g", "price_id" : "10" }
{ "_id" : ObjectId("54576b42ac8d18d02b14649f"), "name" : "Chappie", "weight" : "300g", "price_id" : "20" }
{ "_id" : ObjectId("54576b46ac8d18d02b1464a0"), "name" : "Chappie", "weight" : "1kg", "price_id" : "30" }
{ "_id" : ObjectId("54576b49ac8d18d02b1464a1"), "name" : "Chappie", "weight" : "3kg", "price_id" : "40" }
{ "_id" : ObjectId("54576b64ac8d18d02b1464a2"), "name" : "Royal Canin", "weight" : "1kg", "price_id" : "20" }
{ "_id" : ObjectId("54576b67ac8d18d02b1464a3"), "name" : "Royal Canin", "weight" : "3kg", "price_id" : "30" }
{ "_id" : ObjectId("54576b69ac8d18d02b1464a4"), "name" : "Royal Canin", "weight" : "4kg", "price_id" : "40" }
{ "_id" : ObjectId("54576b6eac8d18d02b1464a5"), "name" : "Royal Canin", "weight" : "10kg", "price_id" : "50" }
> db.supplement_prices.find()
{ "_id" : ObjectId("54576f63ac8d18d02b1464a6"), "id" : "10", "price" : "10EUR" }
{ "_id" : ObjectId("54576f6aac8d18d02b1464a7"), "id" : "20", "price" : "20EUR" }
{ "_id" : ObjectId("54576f6fac8d18d02b1464a8"), "id" : "30", "price" : "30EUR" }
{ "_id" : ObjectId("54576f75ac8d18d02b1464a9"), "id" : "40", "price" : "40EUR" }
{ "_id" : ObjectId("54576f7fac8d18d02b1464aa"), "id" : "50", "price" : "50EUR" }