jdk8使用stream实现两个list集合合并成一个(对象属性的合并) jdk8使用stream实现两个list集合合

一、前言
二、示例

示例1：java8 合并两个 list＜map＞
示例2：java8 合并两个 list＜T＞
示例3：java8 合并两个 list＜T＞，集合个数前者小于后者，要后者
示例4：java8 合并两个 list＜T＞，集合个数前者大于后者，要后者

java使用stream实现list中对象属性的合并:根据两个List中的某个相同字段合并成一条List，包含两个List中的字段

一、前言为什么要用Lambda表达式和Stream流做集合的处理？因为效率高、代码简洁、高端大气上档次！
【jdk8使用stream实现两个list集合合并成一个(对象属性的合并)】（1）描述：比如一个List集合中List<对象1>，该对象1包含A、B和C列; 另外一个List集合中List<对象2>，该对象2包含A、D列;
（2）问题：需要将两个List合成List<对象3>返回,该对象3包含A、B、C、D列
（3）实现：使用stream实现两个list集合合并成一个list集合
简要说明：filter的使用方式为： filter(item -> item的逻辑判断 ) ，其中filter会保留判断条件为true的记录

二、示例
示例1：java8 合并两个 list＜map＞
java8 合并两个 list＜map＞, 并将userId 相同的所有属性合并到一个map中
list1中对象的属性：userId、userName
list2中对象的属性：userId、gender、age
最总集合中对象的属性：userId、userName、gender、age

import java.util.*; import java.util.stream.Collectors; /** * @author qzz */public class ListTest {public static void main(String[] args) {mergeList(); }/*** @Description: 合并两个list,并将userId相同的其它属性合并* @Title: mergeList* @param: @return* @return: List* @throws*/public static List mergeList(){//构建List集合1List list1 = new ArrayList<>(); Map data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100001"); data.put("userName","唐僧"); list1.add(data); data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100002"); data.put("userName","八戒"); list1.add(data); data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100003"); data.put("userName","悟空"); list1.add(data); data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100004"); data.put("userName","沙僧"); list1.add(data); //构建List集合2List list2 = new ArrayList<>(); data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100001"); data.put("gender","男"); data.put("age",20); list2.add(data); data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100002"); data.put("gender","雄"); data.put("age",1000); list2.add(data); data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100003"); data.put("gender","雄"); data.put("age",600); list2.add(data); data=https://www.it610.com/article/new HashMap<>(); data.put("userId","100004"); data.put("gender","男"); data.put("age",800); list2.add(data); //使用stream流把list1和list2根据属性userId合并一个list集合List list = list1.stream().map(m -> {list2.stream().filter(m2-> Objects.equals(m.get("userId"),m2.get("userId"))).forEach(m2-> {m.put("gender",m2.get("gender")); m.put("age",m2.get("age")); }); return m; }).collect(Collectors.toList()); for(Map map:list){System.out.println(map.toString()); }return list; }}

合并运行结果：

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示例2：java8 合并两个 list＜T＞
java8 合并两个 list＜T＞, 并将tickeId相同的所有属性合并到一个T中
list1中对象的属性：ticketId、ticketName
list2中对象的属性：ticketId、saleNum、batchAvailableNum
最总集合中对象的属性：ticketId、ticketName、saleNum、batchAvailableNum

import java.util.*; import java.util.stream.Collectors; /** * @author qzz */public class ListTest1 {public static void main(String[] args) {mergeList(); }/*** @Description: 合并两个list,并将ticketId相同的其它属性合并* @Title: mergeList* @param: @return* @return: List* @throws*/public static List mergeList(){//构建List集合1List list1 = new ArrayList<>(); Ticket data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setTicketName("唐僧"); list1.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100002"); data.setTicketName("八戒"); list1.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100003"); data.setTicketName("悟空"); list1.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100004"); data.setTicketName("沙僧"); list1.add(data); //构建List集合2List list2 = new ArrayList<>(); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setSaleNum("20"); data.setBatchAvailableNum("10"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setSaleNum("20"); data.setBatchAvailableNum("10"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100002"); data.setSaleNum("1000"); data.setBatchAvailableNum("600"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100003"); data.setSaleNum("600"); data.setBatchAvailableNum("100"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100004"); data.setSaleNum("800"); data.setBatchAvailableNum("300"); list2.add(data); //使用stream流把list1和list2根据属性ticketId合并一个list集合List list = list1.stream().map(m -> {list2.stream().filter(m2-> Objects.equals(m.getTicketId(),m2.getTicketId())).forEach(m2-> {m.setSaleNum(m2.getSaleNum()); m.setBatchAvailableNum(m2.getBatchAvailableNum()); }); return m; }).collect(Collectors.toList()); for(Ticket ticket:list){System.out.println(ticket.getTicketId()+","+ticket.getTicketName()+","+ticket.getSaleNum()+","+ticket.getBatchAvailableNum()); }return list; }}

合并运行结果：

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示例3：java8 合并两个 list＜T＞，集合个数前者小于后者，要后者
list1中对象的属性：ticketId、ticketName
list2中对象的属性：ticketId、batchId
最总集合中对象的属性：ticketId、ticketName、batchId
list1:
ticketId:10001 , ticketName:唐僧
ticketId:10002 , ticketName:八戒
list2:
ticketId:10001 , batchId:1
ticketId:10001 , batchId:2
ticketId:10002 , batchId:1
ticketId:10002 , batchId:2
ticketId:10003 , batchId:2
想要的结果：list1合并到 list 2
ticketId:10001 , ticketName:唐僧,batchId:1
ticketId:10001 , ticketName:唐僧,batchId:2
ticketId:10002 , ticketName:八戒,batchId:1
ticketId:10002 , ticketName:八戒,batchId:2
ticketId:10003 , ticketName:八戒,batchId:2
代码实现：

import java.util.ArrayList; import java.util.List; import java.util.Objects; import java.util.stream.Collectors; /** * @author qzz */public class ListTest2 {public static void main(String[] args) {mergeList(); }/*** @Description: 合并两个list,并将userId相同的其它属性合并* @Title: mergeList* @param: @return* @return: List* @throws*/public static List mergeList(){List list1 = new ArrayList<>(); Ticket data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setTicketName("唐僧"); list1.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100002"); data.setTicketName("八戒"); list1.add(data); List list2 = new ArrayList<>(); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setBatchId("1"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setBatchId("2"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100002"); data.setBatchId("1"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100002"); data.setBatchId("2"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100002"); data.setBatchId("3"); list2.add(data); //使用stream流把list1合并到list2集合中，根据ticketId属性List list = list2.stream().map(m -> {list1.stream().filter(m2-> Objects.equals(m.getTicketId(),m2.getTicketId())).forEach(m2-> {m.setTicketId(m2.getTicketId()); m.setTicketName(m2.getTicketName()); }); return m; }).collect(Collectors.toList()); for(Ticket ticket:list){System.out.println(ticket.getTicketId()+","+ticket.getTicketName()+","+ticket.getBatchId()); }return list; }}

合并运行结果：

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示例4：java8 合并两个 list＜T＞，集合个数前者大于后者，要后者
list1中对象的属性：ticketId、ticketName
list2中对象的属性：ticketId、batchId
最总集合中对象的属性：ticketId、ticketName、batchId
list1:
ticketId:10001 , ticketName:唐僧
ticketId:10002 , ticketName:八戒
list2:
ticketId:10001 , batchId:1
ticketId:10001 , batchId:2
想要的结果：list1合并到 list 2，过滤掉batch不存在的数据
ticketId:10001 , ticketName:唐僧,batchId:1
ticketId:10001 , ticketName:唐僧,batchId:2
代码实现：

import java.util.ArrayList; import java.util.List; import java.util.Objects; import java.util.stream.Collectors; /** * @author qzz */public class ListTest3 {public static void main(String[] args) {mergeList(); }/*** @Description: 合并两个list,并将userId相同的其它属性合并* @Title: mergeList* @param: @return* @return: List* @throws*/public static List mergeList(){List list1 = new ArrayList<>(); Ticket data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setTicketName("唐僧"); list1.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100002"); data.setTicketName("八戒"); list1.add(data); List list2 = new ArrayList<>(); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setBatchId("1"); list2.add(data); data=https://www.it610.com/article/new Ticket(); data.setTicketId("100001"); data.setBatchId("2"); list2.add(data); //data=https://www.it610.com/article/new Ticket(); //data.setTicketId("100002"); //data.setBatchId("1"); //list2.add(data); ////data=https://www.it610.com/article/new Ticket(); //data.setTicketId("100002"); //data.setBatchId("2"); //list2.add(data); ////data=https://www.it610.com/article/new Ticket(); //data.setTicketId("100002"); //data.setBatchId("3"); //list2.add(data); //使用stream流把list1合并到list2集合中，根据ticketId属性List list = list2.stream().map(m -> {list1.stream().filter(m2-> Objects.equals(m.getTicketId(),m2.getTicketId())).forEach(m2-> {m.setTicketId(m2.getTicketId()); m.setTicketName(m2.getTicketName()); }); return m; }).collect(Collectors.toList()); for(Ticket ticket:list){System.out.println(ticket.getTicketId()+","+ticket.getTicketName()+","+ticket.getBatchId()); }return list; }}

合并运行结果：