Java Map 通过key过滤

pom文件：

<dependency>
	<groupId>com.google.guava</groupId>
	<artifactId>guava</artifactId>
	<version>31.1-jre</version>
</dependency>

代码：

package com.example.core.utils.collections;

import com.google.common.collect.Maps;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;

public class FilterMapByKeyTest {
    public static void main(String[] args) {
        // 过滤生成map<3的数据
        Map<Integer, String> map = new HashMap<>();
        map.put(1,"a");
        map.put(2,"b");
        map.put(3,"c");
        map.put(4,"d");
        // 方法一：Java原生Map遍历过滤
        Map<Integer, String> newMap = new HashMap<>();
        Set<Map.Entry<Integer, String>> entries = map.entrySet();
        for (Map.Entry<Integer, String> entry : entries) {
            if (entry.getKey() < 3) {
                newMap.put(entry.getKey(),entry.getValue());
            }
        }
        System.out.println(newMap);

        // 方法二：Java8新特性 Lambda表达式过滤
        Map<Integer, String> newMap2 = map.entrySet().stream().filter(m -> m.getKey() < 3).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
        System.out.println(newMap2);

        // 方法三：google.guava 方法
        Map<Integer, String> newMap3 = Maps.filterKeys(map, m -> m < 3);
        System.out.println(newMap3);
    }
}