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 }