1.Collectors.collectingAndThen
下面例子是:在UserEntity的集合中,根据Id属性去重,生成一个新的集合
package com.test.lamdba; import com.test.entity.UserEntity; import java.util.ArrayList; import java.util.Comparator; import java.util.List; import java.util.TreeSet; import java.util.function.Function; import java.util.function.Supplier; import java.util.stream.Collectors; public class TestCollectors { /** * 在UserEntity的集合中,根据Id属性去重,生成一个新的集合 * * @param args */ public static void main(String[] args) { List<UserEntity> userEntityList = new ArrayList<>(); userEntityList.add(new UserEntity("1", "zhangsan")); userEntityList.add(new UserEntity("2", "lisi")); userEntityList.add(new UserEntity("3", "wangwu")); userEntityList.add(new UserEntity("4", "zhaoliu")); userEntityList.add(new UserEntity("2", "sunqi")); userEntityList.add(new UserEntity("3", "qianba")); /** * 根据Id属性去重,生成一个新的集合 */ ArrayList<UserEntity> result = userEntityList.stream().collect( Collectors.collectingAndThen( Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(UserEntity::getId))), ArrayList::new ) ); result.forEach(System.out::println); System.out.println("---------------------------------------"); /** * 上线方法看着过于复杂,把他改成匿名函数的形式写下,便于看懂 */ ArrayList result2 = userEntityList.stream().collect(Collectors.collectingAndThen( Collectors.toCollection(new Supplier<TreeSet<UserEntity>>() { @Override public TreeSet<UserEntity> get() { return new TreeSet<>(Comparator.comparing(UserEntity::getId)); } }), new Function<TreeSet<UserEntity>, ArrayList>() { @Override public ArrayList apply(TreeSet treeSet) { return new ArrayList(treeSet); } } )); result2.forEach(System.out::println); } }
Console:
UserEntity(id=1, name=zhangsan) UserEntity(id=2, name=lisi) UserEntity(id=3, name=wangwu) UserEntity(id=4, name=zhaoliu) --------------------------------------- UserEntity(id=1, name=zhangsan) UserEntity(id=2, name=lisi) UserEntity(id=3, name=wangwu) UserEntity(id=4, name=zhaoliu)
对于Collectors.collectingAndThen、toCollection的使用参考了以下博客:
https://blog.csdn.net/qq_35634181/article/details/108867857
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