java8根据类的某些属性进行去重操作

 

参考： https://stackoverflow.com/questions/23699371/java-8-distinct-by-property

 

 

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.TreeSet;
import java.util.stream.Collectors;

public class Person {
    private Integer id;
    private String firstName;
    private String secondName;

    /**
     *
     */
    public Person() {
        super();
    }

    /**
     * @param id
     * @param firstName
     * @param secondName
     */
    public Person(Integer id, String firstName, String secondName) {
        super();
        this.id = id;
        this.firstName = firstName;
        this.secondName = secondName;
    }

    /*
     * (non-Javadoc)
     * @see java.lang.Object#equals(java.lang.Object)
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        Person other = (Person) obj;
        if (firstName == null) {
            if (other.firstName != null) {
                return false;
            }
        } else if (!firstName.equals(other.firstName)) {
            return false;
        }
        if (id == null) {
            if (other.id != null) {
                return false;
            }
        } else if (!id.equals(other.id)) {
            return false;
        }
        if (secondName == null) {
            if (other.secondName != null) {
                return false;
            }
        } else if (!secondName.equals(other.secondName)) {
            return false;
        }
        return true;
    }

    /**
     * @return the firstName
     */
    public String getFirstName() {
        return firstName;
    }

    /**
     * @return the id
     */
    public Integer getId() {
        return id;
    }

    /**
     * @return the secondName
     */
    public String getSecondName() {
        return secondName;
    }

    /*
     * (non-Javadoc)
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((firstName == null) ? 0 : firstName.hashCode());
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        result = prime * result + ((secondName == null) ? 0 : secondName.hashCode());
        return result;
    }

    /**
     * @param firstName
     *            the firstName to set
     */
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    /**
     * @param id
     *            the id to set
     */
    public void setId(Integer id) {
        this.id = id;
    }

    /**
     * @param secondName
     *            the secondName to set
     */
    public void setSecondName(String secondName) {
        this.secondName = secondName;
    }

    /*
     * (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        return "Person [id=" + id + ", firstName=" + firstName + ", secondName=" + secondName + "]";
    }

    public static void main(String[] args) {
        Person p1 = new Person(1, "wang", "gang");
        Person p2 = new Person(2, "wang", "qiang");
        Person p3 = new Person(3, "wang", "cheng");
        Person p4 = new Person(4, "wang", "qiang");
        Person p5 = new Person(5, "wang", "cheng");
        List<Person> list = new ArrayList<>();
        list.add(p1);
        list.add(p2);
        list.add(p3);
        list.add(p4);
        list.add(p5);
        System.out.println(list);
        /*
         * output:
         * [Person [id=1, firstName=wang, secondName=gang], Person [id=2,
         * firstName=wang, secondName=qiang], Person [id=3, firstName=wang,
         * secondName=cheng]]
         */
        List<Person> distinctList = list.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.comparing(Person::getFirstName))), ArrayList::new));
        /*
         * output:
         * [Person [id=1, firstName=wang, secondName=gang]]
         */
        System.out.println(distinctList);

        List<Person> distinctList1 = list.stream().collect(Collectors
                .collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> {
                    // 根据firstName和secondName进行去重
                    return o.getFirstName() + "," + o.getSecondName();
                }))), ArrayList::new));
        /*
         * output:
         * [Person [id=3, firstName=wang, secondName=cheng], Person [id=1,
         * firstName=wang, secondName=gang], Person [id=2, firstName=wang,
         * secondName=qiang]]
         */
        System.out.println(distinctList1);

        TreeSet<Person> set = new TreeSet<>(Comparator.comparing(o -> {
            // 根据firstName和secondName进行去重
            return o.getFirstName() + "," + o.getSecondName();
        }));
        set.addAll(list);
        /*
         * output:
         * [Person [id=3, firstName=wang, secondName=cheng], Person [id=1,
         * firstName=wang, secondName=gang], Person [id=2, firstName=wang,
         * secondName=qiang]]
         */
        System.out.println(set);
    }
}