List stream 对象属性去重 - 山河永慕~ - 博客园

安宇雨 - 随手采集
2020-11-13 14:54:41
随手采集
0000-未整理-等待研究

单值去重不写了,记录对象去重

随手一个对象:

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@Data
@AllArgsConstructor public class Milk { private Integer key; private String value;
}

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操作:

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package com.yus.util; import java.util.*; import java.util.stream.Collectors; import static java.util.Comparator.comparing; import static java.util.Comparator.comparingLong; import static java.util.stream.Collectors.collectingAndThen; import static java.util.stream.Collectors.toCollection; public class main { public static void main(String[] args) {

    Milk milk0=new Milk(0,"a");
    Milk milk1=new Milk(1,"b");
    Milk milk2=new Milk(0,"c");
    List<Milk> list=new ArrayList<>();
    list.add(milk0);
    list.add(milk1);
    list.add(milk2); //去重
    List<Milk> uniqueMilk = list.stream().collect(
            collectingAndThen(
                    toCollection(() -\> new TreeSet<>(comparing(n->n.getKey()))),ArrayList::new)
    ); for (Milk m:uniqueMilk) {
        System.out.println(m.toString());
    }

}

}

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操作底层是set,视图,collection...一堆东西,还是有点意思的,不记录了,有兴趣可深入

任何Object类型去重...~

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import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.function.Function; import java.util.function.Predicate; import java.util.stream.Collectors; public class TestMain { public static void main(String[] args) {

    List<Map<String, Object>> list = new ArrayList<>();

    Map<String, Object> map = new HashMap<>();
    map.put("id", "11");
    map.put("orderno", "No.1");
    list.add(map);

    Map<String, Object> map1 = new HashMap<>();
    map1.put("id", "2222");
    map1.put("orderno", "No.2");
    list.add(map1);

    Map<String, Object> map2 = new HashMap<>();
    map2.put("id", "33");
    map2.put("orderno", "No.2");
    list.add(map2);

    Map<String, Object> map3 = new HashMap<>();
    map3.put("id", "444");
    map3.put("orderno", "No.1");
    list.add(map3);


    Map<Object, List<Map<String, Object>>> map0 = list.stream().collect(Collectors.groupingBy(e -> e.get("orderno")));

    List<Map<String, Object>> collect = list.stream().filter(distinctByKey(n -> n.get("orderno")))
            .collect(Collectors.toList());

    collect.forEach(System.out::println);
} private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
    ConcurrentHashMap<Object, Boolean> map = new ConcurrentHashMap<>(); return t -> map.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
}

}

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原网址: 访问
创建于: 2020-11-13 14:54:40
目录: default
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