Java 8 Stream之partitioningBy 特殊分组

谁借莪１个温暖的怀抱￠ 2023-10-10 12:16 43阅读 0赞

本文主要讲解：Java 8 Stream之Collectors.partitioningBy()分组示例

功能说明:partitioningBy分区是一种特殊的分组，可以将List划分为两个子List。

## Collectors.partitioningBy() 特殊分组之基础类型用法 ##

功能代码:

/**
    	 * partitioningBy特殊的分组之Integer 类型
    	 */
    	public void partitioningByInteger(){
    		// 数据初始化
    		List<Integer> list = Lists.newArrayList(1, 2, 3, 4, 5, 6, 7, 8);
    		
    		Map<Boolean,List<Integer>> map = list.stream().collect(Collectors.partitioningBy(item ->{
    			return item > 6;
    		}));
    		
    		map.forEach((k, v) -> {
    			System.out.println(k + " = " + v);
    			v.forEach(item -> {
    				System.out.println("item = " + item);
    			});
    		});
    	}

## Collectors.partitioningBy() 特殊分组之Object类型用法 ##

功能代码:

/**
    	 * partitioningBy特殊的分组之Object 类型
    	 */
    	public void partitioningByObject(){
    		// 数据初始化
    		List<Integer> sexs = Arrays.asList(1, 2);
    		List<Integer> ages =  Arrays.asList(4,5,6,7);
    		
    		// 数据集合
    		List<Student> students = new ArrayList<Student>();
    		for (int i = 0; i < 10; i++) {
    			Random random = new Random();
    			Integer sexIndex = random.nextInt(2);
    			Integer ageIndex = random.nextInt(4);
    			Student student = new Student(""+i, "姓名" + i, sexs.get(sexIndex), ages.get(ageIndex), new Date());
    			students.add(student);
    		}
    		
    		// 特殊分组
    		Map<Boolean,List<Student>> map = students.stream().collect(Collectors.partitioningBy(item ->{
    			Student student = item;
    			return student.getAge() == 5;
    		}));
    		
    		map.forEach((k, v) -> {
    			System.out.println(k + " = " + v);
    			v.forEach(item -> {
    				System.out.println("item = " + item);
    			});
    		});
    		
    		// 特殊分组后，List拼接
    		List<Student> container = new ArrayList<Student>();
    	    map.entrySet().stream().map(Map.Entry::getValue).collect(Collectors.toList())
    	      	.stream().forEach(item->{
    	      		container.addAll(item);
    	      	});
    	    if(container != null && container.size() > 0){
    	    	container.stream().forEach(item ->{
    				System.out.println("items = " + item);
    			});
    	    }
    		
    	}

完整源代码:

package com.stream;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.Comparator;
    import java.util.Date;
    import java.util.List;
    import java.util.Map;
    import java.util.Random;
    import java.util.stream.Collectors;
    import java.util.stream.Stream;
    
    import com.google.common.collect.Collections2;
    import com.google.common.collect.Lists;
    import com.stream.Java8GroupBy.Employee;
    import com.stream.entity.Student;
    
    public class Java8PartitioningBy {
    	
    	
    	/**
    	 * partitioningBy特殊的分组之Integer 类型
    	 */
    	public void partitioningByInteger(){
    		// 数据初始化
    		List<Integer> list = Lists.newArrayList(1, 2, 3, 4, 5, 6, 7, 8);
    		
    		Map<Boolean,List<Integer>> map = list.stream().collect(Collectors.partitioningBy(item ->{
    			return item > 6;
    		}));
    		
    		map.forEach((k, v) -> {
    			System.out.println(k + " = " + v);
    			v.forEach(item -> {
    				System.out.println("item = " + item);
    			});
    		});
    	}
    	
    	/**
    	 * partitioningBy特殊的分组之Object 类型
    	 */
    	public void partitioningByObject(){
    		// 数据初始化
    		List<Integer> sexs = Arrays.asList(1, 2);
    		List<Integer> ages =  Arrays.asList(4,5,6,7);
    		
    		// 数据集合
    		List<Student> students = new ArrayList<Student>();
    		for (int i = 0; i < 10; i++) {
    			Random random = new Random();
    			Integer sexIndex = random.nextInt(2);
    			Integer ageIndex = random.nextInt(4);
    			Student student = new Student(""+i, "姓名" + i, sexs.get(sexIndex), ages.get(ageIndex), new Date());
    			students.add(student);
    		}
    		
    		// 特殊分组
    		Map<Boolean,List<Student>> map = students.stream().collect(Collectors.partitioningBy(item ->{
    			Student student = item;
    			return student.getAge() == 5;
    		}));
    		
    		map.forEach((k, v) -> {
    			System.out.println(k + " = " + v);
    			v.forEach(item -> {
    				System.out.println("item = " + item);
    			});
    		});
    		
    		// 特殊分组后，List拼接
    		List<Student> container = new ArrayList<Student>();
    	    map.entrySet().stream().map(Map.Entry::getValue).collect(Collectors.toList())
    	      	.stream().forEach(item->{
    	      		container.addAll(item);
    	      	});
    	    if(container != null && container.size() > 0){
    	    	container.stream().forEach(item ->{
    				System.out.println("items = " + item);
    			});
    	    }
    		
    	}
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		Java8PartitioningBy instance = new Java8PartitioningBy();
    		instance.partitioningByInteger();
    		instance.partitioningByObject();
    	}
    
    }

package com.stream.entity;
    
    import java.util.Date;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    import lombok.NoArgsConstructor;
    
    @AllArgsConstructor
    @NoArgsConstructor
    @Data
    public class Student {
    
    	private String id;
    	private String name;
    	private Integer sex;
    	private Integer age;
    	private Date birthDay;
    }

pom.xml 文件添加如下依赖:

<dependency>
    			<groupId>com.google.guava</groupId>
    			<artifactId>guava</artifactId>
    			<version>28.2-jre</version>
    		</dependency>
    		<dependency>
    			<groupId>org.projectlombok</groupId>
    			<artifactId>lombok</artifactId>
    			<version>1.18.10</version>
    			<scope>provided</scope>
    		</dependency>