java8根据某一属性过滤去重
最近小编刚接触到java8特性，在不知道有java8特性的时候，一个for循环套一个for循环，自从接触大java8，为自己省了很多事，节省了很多代码量.
根据list某一属性去重
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//根据id去重 examRoomModelLists = examRoomModelLists.stream().collect(Collectors.collectingAndThen(Collectors.toCollection( // 利用 TreeSet 的排序去重构造函数来达到去重元素的目的 // 根据firstName去重 () -> new TreeSet<>(Comparator测试数据paring(ExamRoomModel::getId))), ArrayList:: new )); |
过滤StudentExamState=0的数据
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em.setNoLoginExamineeCount((examinee.stream().map(ExamineeEntity::getStudentExamState).filter(x -> x == 0 ).collect(Collectors.toList())).size()); } |
过滤ExamRoomStudentCount=0的数据
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List<ExamRoomModel> filterList = examRoomModelLists.stream().filter(ExamRoomModel -> !Objects.equals(ExamRoomModel.getExamRoomStudentCount(), 0 )).collect(Collectors.toList()); |
是不是很方便，换成以前过滤去重不知道要写多少横代码，现在一行解决.
Java8 stream根据对象字段去重
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public class Java8StreamTest { public static class Book{ private String id; private String name; public Book(String id, String name) { this .id = id; this .name = name; } public String getId() { return id; } public void setId(String id) { this .id = id; } public String getName() { return name; } public void setName(String name) { this .name = name; } @Override public String toString() { return "Book{" + "id='" + id + '\ '' + ", name='" + name + '\ '' + '}' ; } } @Test public void testUnique(){ List<Book> books = Lists.newArrayList( new Book( "1" , "1" ), new Book( "2" , "2" ), new Book( "3" , "3" ), new Book( "2" , "2" )); //使用TreeSet去重 List<Book> unique1 = books.stream().collect( collectingAndThen(toCollection(() -> new TreeSet<>(Comparator测试数据paring(o -> o.getId()))), ArrayList:: new )); System.out.println(unique1); //使用map去重 List<Book> unique2 = books.stream() .filter(distinctByKey(o -> o.getId())) .collect(Collectors.toList()); System.out.println(unique2); } public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) { Map<Object, Boolean> seen = new ConcurrentHashMap<>(); System.out.println( "这个函数将应用到每一个item" ); return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null ; } } |
stream对list中的对象进行去重
首先我们有一个对象属性如下
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@Data public class Person { private String id; private String name; private String sex; } |
我们根据属性name来去重，去重代码如下
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List<Person> persons = new ArrayList(); //赋值初始化过程省略 List<Person> uniqueByName = persons.stream().collect( Collectors.collectingAndThen( Collectors.toCollection(() -> new TreeSet<>(Comparator测试数据paring(Person::getName))), ArrayList:: new ) ); |
根据name,sex两个属性去重
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List<Person> persons = new ArrayList(); //赋值初始化过程省略 List<Person> uniqueByNameAndSex = persons.stream().collect( Collectors. collectingAndThen( Collectors.toCollection(() -> new TreeSet<>(Comparator测试数据paring(o -> o.getName() + ";" + o.getSex()))), ArrayList:: new ) ); |
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。
原文链接：https://blog.csdn.net/yyx3214/article/details/85949622
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