Java中list集合stream流去重

水深无声 2023-09-27 19:17 17阅读 0赞

## Java中list集合stream流去重 ##

### 1. List单个字段去重 ###

list.stream().distinct().collect(Collectors.toList());

###  ###

### 2. List对象集合根据一个或者多个字段去重 ###

准备类：

@Data
    public class Book {
        
        private Long id;
        private String name;
        private Double price;
    }

（1）根据单字段name去重

bookList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Book::getName))), ArrayList::new));

（2）根据多字段name price去重

bookList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(book -> book.getName() + "-" + book.getPrice()))), ArrayList::new));

（3）示例

import java.util.ArrayList;
    import java.util.Comparator;
    import java.util.List;
    import java.util.TreeSet;
    import java.util.stream.Collectors;
    import lombok.Data;
     
    @Data
    public class Book {
        
        private Long id;
        private String name;
        private Double price;
     
        public Book(Long id, String name, Double price) {
        
            this.id = id;
            this.name = name;
            this.price = price;
        }
     
        public static void main(String[] args) {
        
            List<Book> bookList = new ArrayList<>();
            bookList.add(new Book(1L, "书本1", 1.1));
            bookList.add(new Book(2L, "书本1", 1.1));
            bookList.add(new Book(3L, "书本2", 2.2));
            bookList.add(new Book(4L, "书本2", 4.4));
            // 根据单字段name去重
            List<Book> bookList1 = bookList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Book::getName))), ArrayList::new));
            System.out.println("单字段去重结果：" + bookList1.toString());
            // 根据多字段name price去重
            List<Book> bookList2 = bookList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(book -> book.getName() + "-" + book.getPrice()))), ArrayList::new));
            System.out.println("多字段去重结果：" + bookList2.toString());
        }
    }

输出打印结果

单字段去重结果：[Book(id=1, name=书本1, price=1.1), Book(id=3, name=书本2, price=2.2)]
    多字段去重结果：[Book(id=1, name=书本1, price=1.1), Book(id=3, name=书本2, price=2.2), Book(id=4, name=书本2, price=4.4)]