1 /*
   2  * Copyright (c) 2013 Oracle and/or its affiliates. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  *
   8  *   - Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  *
  11  *   - Redistributions in binary form must reproduce the above copyright
  12  *     notice, this list of conditions and the following disclaimer in the
  13  *     documentation and/or other materials provided with the distribution.
  14  *
  15  *   - Neither the name of Oracle nor the names of its
  16  *     contributors may be used to endorse or promote products derived
  17  *     from this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
  20  * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  24  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  25  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  26  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  27  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  28  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  29  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  */
  31 
  32 /*
  33  * This source code is provided to illustrate the usage of a given feature
  34  * or technique and has been deliberately simplified. Additional steps
  35  * required for a production-quality application, such as security checks,
  36  * input validation and proper error handling, might not be present in
  37  * this sample code.
  38  */
  39 package stream;
  40 
  41 import stream.data.Customer;
  42 import stream.data.Vendor;
  43 import java.util.ArrayList;
  44 import java.util.List;
  45 import java.util.Map;
  46 import java.util.Set;
  47 import java.util.function.Function;
  48 import java.util.stream.Collectors;
  49 import static java.util.stream.Collectors.*;
  50 import java.util.stream.Stream;
  51 
  52 /**
  53  * A demo shows how does Stream's flatMap works. Demo shows tabulate stream
  54  * element to single element stream or empty stream
  55  *
  56  * @author tyan
  57  */
  58 public class Tabulate extends DemoHelper {
  59     /**
  60      * Join vendor and customer that in same country. note not all vendor
  61      * has customer
  62      * @return  a list of customer-vendor pair which in same country
  63      */
  64     public static Map<Customer, List<Vendor>> sameCountryCustomerAndVendors() {
  65         Map<String, List<Vendor>> countryToVendors = vendors.stream().
  66                 // group vendors by their country
  67                 collect(groupingBy(Vendor::getCountry));
  68         //Find customer in countryToVendors with key as customer's country
  69         Function<Customer, List<Vendor>> vendorsInSameCustomerCountry
  70                 = customer-> countryToVendors.getOrDefault(
  71                         customer.getCountry(), new ArrayList<>());
  72         //Map customer to vendor who are same country as customer's
  73         return customers.stream().
  74                 filter(c -> countryToVendors.containsKey(c.getCountry())).
  75                 collect(toMap(Function.identity(), vendorsInSameCustomerCountry));
  76     }
  77 
  78     /**
  79      * flatMap can generate empty stream, sometimes it's helpful for ruling
  80      * out data
  81      * @return   a string set who is either customer and vendor both.
  82      */
  83     public static Set<String> bothCustomerAndVendor() {
  84         Set<String> vendorsName = vendors.stream().
  85                 map(Vendor::getVendorName).
  86                 collect(toSet());
  87         return customers.stream().
  88                 //map customer to its name
  89                 map(Customer::getCompanyName).
  90                 //query vendor set with customer's name, if exist, create
  91                 //a stream with single element customer name, if doesn't, create
  92                 //an empty stream
  93                 flatMap(c -> vendorsName.contains(c)
  94                         ? Stream.of(c) : Stream.empty()).
  95                 //convert all match name into a set
  96                 collect(Collectors.toSet());
  97     }
  98 }