java stream 根据多字段去重

原文链接：Java 8 stream distinct by multiple fields - HowToDoInJava

import java.util.ArrayList;
import java.util.Arrays;
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 DistinctByMultiFields {

    public static void main(String[] args) {
        List recordsList = getRecords();

        List list = recordsList.stream()
                .filter(distinctByKeys(Record::getId, Record::getName))
                .collect(Collectors.toList());

        System.out.println(list);
    }

    private static  Predicate distinctByKeys(Function... keyExtractors) {
        final Map, Boolean> seen = new ConcurrentHashMap<>();

        return t ->
        {
            final List keys = Arrays.stream(keyExtractors)
                    .map(ke -> ke.apply(t))
                    .collect(Collectors.toList());

            return seen.putIfAbsent(keys, Boolean.TRUE) == null;
        };
    }

		private static ArrayList getRecords() {
        ArrayList records = new ArrayList<>();

        records.add(new Record(1l, 10l, "record1", "record1@email.com", "India"));
        records.add(new Record(1l, 20l, "record1", "record1@email.com", "India"));
        records.add(new Record(2l, 30l, "record2", "record2@email.com", "India"));
        records.add(new Record(2l, 40l, "record2", "record2@email.com", "India"));
        records.add(new Record(3l, 50l, "record3", "record3@email.com", "India"));

        return records;
    }
}

public class Record {
    private long id;
    private long count;
    private String name;
    private String email;
    private String location;

    public Record(long id, long count, String name,
                  String email, String location) {
        super();
        this.id = id;
        this.count = count;
        this.name = name;
        this.email = email;
        this.location = location;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public long getCount() {
        return count;
    }

    public void setCount(long count) {
        this.count = count;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    @Override
    public String toString() {
        return "Record [id=" + id + ", count=" + count + ", name=" + name +
                ", email=" + email + ", location="
                + location + "]";
    }
    }