Java中Comparator的示例

业务需求：

先按参与人数降序，再按排名之和升序

人数：perTotal ，排名之和：rankTotal

完整代码：

	@Override
	public JSONObject getTopUnitOfGameRanking(List<Map<Long, Integer>> userMap,
			int limit) {
		JSONObject json = new JSONObject();
		List<JSONObject> list = new ArrayList<JSONObject>();
		List<JSONObject> lists = new ArrayList<JSONObject>();
		List<Long> userIds = new ArrayList<Long>();

		for(Map<Long, Integer> userRanking : userMap){
			for(Long userId : userRanking.keySet()){
				userIds.add(userId);
			}
		}

		if (userIds != null && userIds.size() > 0) {
			List<Object> param = new ArrayList<Object>();
			StringBuilder builder = new StringBuilder();
			builder.append("select  unit_id,count(user_id) as pertotal from t_user_expand where unit_id !=0 and user_id in (  ");
			for (int i = 0; i < userIds.size(); i++) {
				if (i != 0) {
					builder.append(",");
				}
				builder.append("?");
				param.add(userIds.get(i));
			}
			builder.append(" )  GROUP BY unit_id order by pertotal desc limit ? ");
			param.add(limit);
			//final List<Long> unitIds = new ArrayList<Long>();
			list = primaryJdbcTemplate.query(builder.toString(), param.toArray(),new RowMapper<JSONObject>() {

				@Override
				public JSONObject mapRow(ResultSet rs, int rowNum) throws SQLException {
					JSONObject o = new JSONObject();
					o.put("unitId", rs.getLong("unit_id"));
					o.put("perTotal", rs.getLong("pertotal"));
					return o;
				}
			});

			List<Object> params = new ArrayList<Object>();
			StringBuilder builders = new StringBuilder();
			builders.append("select unit_id,user_id  from  t_user_expand where unit_id !=0 and user_id in( ");
			for (int i = 0; i < userIds.size(); i++) {
				if (i != 0) {
					builders.append(",");
				}
				builders.append("?");
				params.add(userIds.get(i));
			}
			builders.append(" ) limit ? ");
			params.add(limit);
			lists = primaryJdbcTemplate.query(builders.toString(), params.toArray(),new RowMapper<JSONObject>() {

				@Override
				public JSONObject mapRow(ResultSet rs, int rowNum) throws SQLException {
					JSONObject o = new JSONObject();
					o.put("unitId", rs.getLong("unit_id"));
					o.put("user_id", rs.getLong("user_id"));
					return o;
				}
			});

			for(JSONObject obj : lists){ // 遍历 “用户id”关联的“府id”
				for(Map<Long, Integer> user : userMap){ //由“用户id”获取对应的排名
					Integer rank =user.get(obj.get("user_id"));
					if(null == rank){
						rank = 0;
					}
					for(JSONObject object : list){
						if(((Long)object.get("unitId")).compareTo((Long)obj.get("unitId"))==0){
							Integer oldRankTotal = (Integer)object.get("rankTotal");
							if(null == oldRankTotal){
								oldRankTotal = 0;
							}
							object.put("rankTotal", oldRankTotal + rank);
						}
					}
				}
			}
		}

		Collections.sort(list, new Comparator<JSONObject>(){
			/**
			 * 先按参与人数降序，再按排名之和升序
			 */
			@Override
			public int compare(JSONObject o1, JSONObject o2) {

				Long perTotal1 = (Long)o1.get("perTotal");
				Long perTotal2 = (Long)o2.get("perTotal");
				Integer rankTotal1 = (Integer)o1.get("rankTotal");
				Integer rankTotal2 = (Integer)o2.get("rankTotal");

				if(perTotal1.compareTo(perTotal2) > 0){
					return -1;
				}else if(perTotal1.compareTo(perTotal2) < 0){
					return 1;
				}else{
					if(rankTotal1.compareTo(rankTotal2) > 0){
						return 1;
					}else if(rankTotal1.compareTo(rankTotal2) < 0){
						return -1;
					}else{
						return 0;
					}
				}
			}

		});

		json.put("data", list);
		return json;
	}

关键部分代码（在人数相同的情况下，比较排名之和）：

		List<JSONObject> list = new ArrayList<JSONObject>();
		Collections.sort(list, new Comparator<JSONObject>(){
			/**
			 * 先按参与人数降序，再按排名之和升序
			 */
			@Override
			public int compare(JSONObject o1, JSONObject o2) {

				Long perTotal1 = (Long)o1.get("perTotal");
				Long perTotal2 = (Long)o2.get("perTotal");
				Integer rankTotal1 = (Integer)o1.get("rankTotal");
				Integer rankTotal2 = (Integer)o2.get("rankTotal");

				if(perTotal1.compareTo(perTotal2) > 0){
					return -1;
				}else if(perTotal1.compareTo(perTotal2) < 0){
					return 1;
				}else{
					if(rankTotal1.compareTo(rankTotal2) > 0){
						return 1;
					}else if(rankTotal1.compareTo(rankTotal2) < 0){
						return -1;
					}else{
						return 0;
					}
				}
			}

		});