两个list集合对象属性的合并

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

public class Test3 {
    public static void main(String[] args){

        List<Map<String,Object>> list1 = new ArrayList<>();
        Map<String,Object> data=new HashMap<>();
        data.put("userId","100001");
        data.put("userName","唐僧");
        list1.add(data);
        data=new HashMap<>();
        data.put("userId","100002");
        data.put("userName","八戒");
        list1.add(data);

        List<Map<String,Object>> list2 = new ArrayList<>();
        data=new HashMap<>();
        data.put("userId","100001");
        data.put("gender","男");
        data.put("age",20);
        list2.add(data);
        data=new HashMap<>();
        data.put("userId","100002");
        data.put("gender","雄");
        data.put("age",1000);
        list2.add(data);

        System.out.println(list1);
        System.out.println(list2);

        //使用stream流把list1和list2根据属性userId合并一个list集合
        list1.stream().map(m1 -> {
            list2.stream().filter(m2 -> m1.get("userId").equals(m2.get("userId"))).forEach( m2 -> {
                m1.put("gender", m2.get("gender"));
                m1.put("age", m2.get("age"));
            });
            return m1;
        }).collect(Collectors.toList());

        System.out.println(list1);
        System.out.println(list2);
    }
}

运行结果：

结果可见，userId 相同的所有属性合并到集合 list1中。

两个list集合对象属性值运算

合并两个 list＜map＞, 并将 userId 相同的某个属性值进行运算

list1中对象的属性：id、name、amount

list2中对象的属性：id、name、amount

最总集合中对象的属性：id、name、amount（金额进行累加）

User ：

@Data
@AllArgsConstructor
public class User {
    public String id;
    public String name;
    public BigDecimal amount;
}

public class Test3 {
    public static void main(String[] args){

        List<User> userList1 = new ArrayList<>();
        User user1 = new User("1001", "lili", new BigDecimal("100.5"));
        User user2 = new User("1002", "lucy", new BigDecimal("100.66"));
        userList1.add(user1);
        userList1.add(user2);

        List<User> userList2 = new ArrayList<>();
        User user3 = new User("1001", "lili", new BigDecimal("200.5"));
        User user4 = new User("1002", "lucy", new BigDecimal("200.66"));
        User user5 = new User("1003", "jack", new BigDecimal("200.88"));
        userList2.add(user3);
        userList2.add(user4);
        userList2.add(user5);

        System.out.println("userList1：" + userList1);
        System.out.println("userList2：" + userList2);

        List<User> collect = userList1.stream().map(u1 -> {
            userList2.stream().filter(u2 -> u2.getId().equals(u1.getId())).forEach(u2 -> {
                if (u2.getAmount() != null) {
                    u1.setAmount(u1.getAmount().add(u2.getAmount()));
                }
            });
            return u1;
        }).collect(Collectors.toList());

        System.out.println("userList1：" + userList1);
        System.out.println("collect：" + collect);
        System.out.println("userList2：" + userList2);
    }
}

运行结果：

结果可见，相同 id 记录的 amount 属性值进行了累计运算。

结果可见，userList1 的值发生了改变，如果不想改变原集合内容：

public class Test3 {
    public static void main(String[] args){

        List<User> userList1 = new ArrayList<>();
        User user1 = new User("1001", "lili", new BigDecimal("100.5"));
        User user2 = new User("1002", "lucy", new BigDecimal("100.66"));
        userList1.add(user1);
        userList1.add(user2);

        List<User> userList2 = new ArrayList<>();
        User user3 = new User("1001", "lili", new BigDecimal("200.5"));
        User user4 = new User("1002", "lucy", new BigDecimal("200.66"));
        User user5 = new User("1003", "jack", new BigDecimal("200.88"));
        userList2.add(user3);
        userList2.add(user4);
        userList2.add(user5);

        ArrayList<User> result = new ArrayList<>();

        List<User> collect = userList1.stream().map(u1 -> {
            userList2.stream().filter(u2 -> u2.getId().equals(u1.getId())).forEach(u2 -> {
                if (u2.getAmount() != null) {
                    BigDecimal add = u1.getAmount().add(u2.getAmount());
                    result.add(new User(u1.getId(), u1.getName(), add));
                }
            });
            return u1;
        }).collect(Collectors.toList());

        System.out.println("userList1：" + userList1);
        System.out.println("userList2：" + userList2);
        System.out.println("collect：" + collect);
        System.out.println("result： " + result);
    }
}

运行结果：

新增集合 result 进行最终结果存储，原集合内容不变。