map具有相同value转变为Map<key,ArrayList<value>>

Map<String,String> map = new HashMap<String,String>();
map.put("1","v1");
map.put("2","v1");
map.put("3","v1");
map.put("4","v2");
map.put("5","v2");
map.put("6","v2");
Map<String,ArrayList<String>> new_map = new HashMap<String,ArrayList<String>>();
Iterator<Entry<String,String>> iter = map.entrySet().iterator();
while(iter.hasNext()){
    Entry<String,String> entry = iter.next();
    String key = entry.getKey();
    String value = entry.getValue();
    if (new_map.get(key) == null) {
        ArrayList<JSONObject> arrList= new ArrayList<JSONObject>();
        evtDocList.add(key);
        new_map.put(value, arrList);
    } else {
        if (!new_map.get(value).contains(key))    
        {
            new_map.get(value).add(key);
        }
}
}

这样就把具有相同value的key赋值给了arrayList，从而生成以value作为key的新map
但是，如果arrayList中需要不同类型比如String、Integer、double等，那么就需要使用泛型来支持。

public class test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		JsonUtils utils = JsonUtils.getInstance();
		Map<String, ArrayList<String>> t1 = new HashMap<String, ArrayList<String>>();
		Map<String, ArrayList<Integer>> t2 = new HashMap<String, ArrayList<Integer>>();
		utils.jsonMap(t2, "a", 2);
		utils.jsonMap(t2, "a", 3);
		utils.jsonMap(t2, "a", 4);
		utils.jsonMap(t1, "b", "t1");
		utils.jsonMap(t1, "b", "t2");
		utils.jsonMap(t1, "b", "t3");
		Iterator<Entry<String,ArrayList<Integer>>> iter = t2.entrySet().iterator();
		while(iter.hasNext()){
			Entry<String,ArrayList<Integer>> entry = iter.next();
			String key = entry.getKey();
			ArrayList<Integer> value = entry.getValue();
			for(Integer str : value){
				System.out.println(key+"========="+str);
			}
		}
		Iterator<Entry<String,ArrayList<String>>> iter2 = t1.entrySet().iterator();
		while(iter2.hasNext()){
			Entry<String,ArrayList<String>> entry = iter2.next();
			String key = entry.getKey();
			ArrayList<String> value = entry.getValue();
			for(String str : value){
				System.out.println(key+"========="+str);
			}
		}
	}

}

public final class JsonUtils {
	private static JsonUtils INSTANCE = new JsonUtils();
	private JsonUtils()
	{
		
	}
	public static JsonUtils getInstance(){
		return INSTANCE;
	}
	public <T> Map<String, ArrayList<T>> jsonMap(Map<String, ArrayList<T>> map,String key,T value){
		if (map.get(key) == null) {
			ArrayList<T> eIdList = new ArrayList<T>();
			eIdList.add(value);
			map.put(key, eIdList);
		} else {
			if (!map.get(key).contains(value)) {
				map.get(key).add(value);
			}
		}
		return map;
	}
}

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2 楼 wt22260 2012-08-19  

wt22260 写道

1 楼 wt22260 2012-08-19