commons-collections集合类型-MultiMap

末蓝、 2022-08-14 04:52 9阅读 0赞

在日常的开发工作中，我们有的时候需要构造像Map<K, List<V>>或者Map<K, Set<V>>这样比较复杂的集合类型的数据结构，如果是自己写，需要额外大量的代码，此时，就可以使用到commons-collections里面的MultiMap

代码如下

首先加入依赖：

<dependency>
    	<groupId>commons-collections</groupId>
    	<artifactId>commons-collections</artifactId>
    	<version>3.2.2</version>
    </dependency>

package org.osc.hazelcast.coll;
    
    import java.util.HashMap;
    import java.util.HashSet;
    
    import org.apache.commons.collections.MultiMap;
    import org.apache.commons.collections.map.MultiValueMap;
    
    public class MultiMapTest 
    {
    	static void list()
    	{
    		/**
    		 * 默认是取出来的是list
    		 */
    		MultiMap mm = new MultiValueMap();
    		mm.put("唐朝", new User("1", "李渊"));
    		mm.put("唐朝", new User("2", "李世民"));
    		mm.put("唐朝", new User("3", "李治"));
    		mm.put("唐朝", new User("4", "李显"));
    		mm.put("唐朝", new User("4", "李旦"));
    		
    		mm.put("宋朝", new User("5", "赵匡胤"));
    		mm.put("宋朝", new User("6", "赵光义"));
    		
    		System.out.println(mm.get("唐朝"));
    		System.out.println(mm.get("唐朝").getClass());
    	}
    	
    	static void set()
    	{
    		/**
    		 * 如果取出来的是set , 需要调用decorate方法
    		 */
    		MultiMap mm = MultiValueMap.decorate(new HashMap<String, User>(), HashSet.class);
    		mm.put("唐朝", new User("1", "李渊"));
    		mm.put("唐朝", new User("2", "李世民"));
    		mm.put("唐朝", new User("3", "李治"));
    		mm.put("唐朝", new User("4", "李显"));
    		mm.put("唐朝", new User("4", "李旦"));
    		
    		mm.put("宋朝", new User("5", "赵匡胤"));
    		mm.put("宋朝", new User("6", "赵光义"));
    		
    		System.out.println(mm.get("唐朝"));
    		System.out.println(mm.get("唐朝").getClass());
    	}
    	
    	public static void main(String[] args)
    	{
    		list();
    		System.out.println("-----------------");
    		set();
    	}
    
    }
    class User
    {
    	private String id;
    	private String name;
    	public int hashCode() {
    		return id.hashCode();
    	}
    	public boolean equals(Object obj)
    	{
    		User user = (User)obj;
    		return this.id.equals(user.id);
    	}
    	public User(String id, String name)
    	{
    		this.id = id;
    		this.name = name;
    	}
    	public String toString()
    	{
    		return "User [id=" + id + ", name=" + name + "]";
    	}
    }

运行，输出如下：

\[User \[id=1, name=李渊\], User \[id=2, name=李世民\], User \[id=3, name=李治\], User \[id=4, name=李显\], User \[id=4, name=李旦\]\]  
class java.util.ArrayList  
\-----------------  
\[User \[id=1, name=李渊\], User \[id=2, name=李世民\], User \[id=3, name=李治\], User \[id=4, name=李显\]\]  
class java.util.HashSet