guava集合分组

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

import com.google.common.base.Function;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multimaps;

import lombok.Getter;
import lombok.Setter;

@Setter
@Getter
class Goods {
	private Integer id;
	private Integer groupId;
	private String name;
	
	public String toString() {
		return "{id="+id + ", groupId=" + groupId + ", name=" + name + "}";
	}
}
public class TxAspect {
	public static void main(String[] args) {
	    List<Goods> list = new ArrayList<>();
	    {
	    	Goods e = new Goods();
	    	e.setId(1);
	    	e.setGroupId(1);
	    	e.setName("商品1");
	    	list.add(e);
	    }

	    {
	    	Goods e = new Goods();
	    	e.setId(3);
	    	e.setGroupId(3);
	    	e.setName("商品3");
	    	list.add(e);
	    }
	    {
	    	Goods e = new Goods();
	    	e.setId(4);
	    	e.setGroupId(2);
	    	e.setName("商品4");
	    	list.add(e);
	    }
	    {
	    	Goods e = new Goods();
	    	e.setId(5);
	    	e.setName("商品5");
	    	list.add(e);
	    }
	    {
	    	Goods e = new Goods();
	    	e.setId(2);
	    	e.setGroupId(2);
	    	e.setName("商品2");
	    	list.add(e);
	    }
	    //根据groupId分组, 如果groupId为null, 则放到默认为0的group下
	    Function<Goods, Integer> fun = new Function<Goods, Integer>() {
	        @Override
	        public Integer apply(Goods input) {
	            if (input.getGroupId() == null) {
	                return 0;
	            }
	            return input.getGroupId();
	        }
	    };
	    Multimap<Integer, Goods> index = Multimaps.index(list, fun);
	    Map<Integer, Collection<Goods>> map = index.asMap();
	    for (Map.Entry<Integer, Collection<Goods>> entry : map.entrySet()) {
	    	System.out.println(entry.getKey() + " <---> " + entry.getValue());
	    }
	}
}