Java8 List去重（单属性或组合属性）

朱雀 2022-12-15 03:47 150阅读 0赞

code:

package com.demo.jdk8.collectors;
     
    import com.google.common.collect.Lists;
    import org.junit.jupiter.api.Test;
     
    import java.util.ArrayList;
    import java.util.Comparator;
    import java.util.List;
    import java.util.TreeSet;
    import java.util.stream.Collectors;
     
    /**
     * @author Shanks
     * @date 2018-10-15
     */
    public class CollectingAndThenTest {
     
        @Test
        void testCollectingAndThen() {
     
            UserOrder order0 = new UserOrder("年会", "张三", "box0001");
            UserOrder order1 = new UserOrder("婚庆", "张三", "box0002");
            UserOrder order2 = new UserOrder("旅游", "李四", "box0003");
            UserOrder order3 = new UserOrder("发布会", "张三", "box0002");
            UserOrder order4 = new UserOrder("旅游", "李四", "box0004");
     
            List<UserOrder> list = Lists.newArrayList(order0, order1, order2, order3, order4);
     
            System.out.println("=====>只根据单一属性photographerName进行去重");
            // <R, A> R collect(Collector<? super T, A, R> collector);
            // collectingAndThen(Collector<T, A, R> downstream, Function<R, RR> finisher)
            // toCollection(Supplier<C> collectionFactory)
            ArrayList<UserOrder> distinctByName = list.stream()
                    .collect(
                            Collectors.collectingAndThen(
                                    Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(UserOrder::getPhotographerName))),
                                    userOrders -> new ArrayList<>(userOrders)
                            )
                    );
            distinctByName.forEach(System.out::println);
     
            System.out.println("=====>同时根据photographerName和deviceCode两个属性进行去重");
            ArrayList<UserOrder> distinctByNameAndCode = list.stream()
                    .collect(
                            Collectors.collectingAndThen(
                                    Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(userOrder -> userOrder.getPhotographerName() + userOrder.getDeviceCode()))),
                                    ArrayList::new
                            )
                    );
            distinctByNameAndCode.forEach(System.out::println);
        }
    }

result:

=====>只根据单一属性photographerName进行去重
    UserOrder{shootingTheme='年会', photographerName='张三', deviceCode='box0001'}
    UserOrder{shootingTheme='旅游', photographerName='李四', deviceCode='box0003'}
     
    =====>同时根据photographerName和deviceCode两个属性进行去重
    UserOrder{shootingTheme='年会', photographerName='张三', deviceCode='box0001'}
    UserOrder{shootingTheme='婚庆', photographerName='张三', deviceCode='box0002'}
    UserOrder{shootingTheme='旅游', photographerName='李四', deviceCode='box0003'}
    UserOrder{shootingTheme='旅游', photographerName='李四', deviceCode='box0004'}

entity:

package com.demo.jdk8.collectors;
     
    /**
     * @author Shanks
     * @date 2018-10-16
     */
    public class UserOrder {
     
        /**
         * 拍摄主题
         */
        private String shootingTheme;
        /**
         * 摄影师
         */
        private String photographerName;
        /**
         * 设备编号
         */
        private String deviceCode;
     
        public UserOrder() {
        }
     
        public UserOrder(String shootingTheme, String photographerName, String deviceCode) {
            this.shootingTheme = shootingTheme;
            this.photographerName = photographerName;
            this.deviceCode = deviceCode;
        }
     
        @Override
        public String toString() {
            return "UserOrder{" +
                    "shootingTheme='" + shootingTheme + '\'' +
                    ", photographerName='" + photographerName + '\'' +
                    ", deviceCode='" + deviceCode + '\'' +
                    '}';
        }
     
        public String getShootingTheme() {
            return shootingTheme;
        }
     
        public void setShootingTheme(String shootingTheme) {
            this.shootingTheme = shootingTheme;
        }
     
        public String getPhotographerName() {
            return photographerName;
        }
     
        public void setPhotographerName(String photographerName) {
            this.photographerName = photographerName;
        }
     
        public String getDeviceCode() {
            return deviceCode;
        }
     
        public void setDeviceCode(String deviceCode) {
            this.deviceCode = deviceCode;
        }
    }