list 按照元素的某個(gè)字段去重
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
private Integer age;
private String name;
}
測(cè)試數(shù)據(jù)
List<Student> studentList = Lists.newArrayList(); studentList.add(new Student(28, "river")); studentList.add(new Student(12, "lucy")); studentList.add(new Student(33, "frank")); studentList.add(new Student(33, "lucy"));
java8 通過(guò)tree set 去重
List<Student> studentDistinctList = studentList.stream() .collect(Collectors.collectingAndThen (Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(t -> t.getName()))), ArrayList::new ) ); System.out.println(new Gson().toJson(studentDistinctList));
擴(kuò)展distinct 方法去重
List<Student> studentDistinct2List = studentList.stream().filter(StreamUtil.distinctByKey(t->t.getName())) .collect(Collectors.toList()); System.out.println(new Gson().toJson(studentDistinct2List));
工具類
public class StreamUtil {
/**
* https://stackoverflow.com/questions/23699371/java-8-distinct-by-property
* @param keyExtractor
* @param <T>
* @return
*/
public static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
Set<Object> seen = ConcurrentHashMap.newKeySet();
return t -> seen.add(keyExtractor.apply(t));
}
}
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