参考 http://blog.csdn.net/lk\_blog/article/details/7685190

满足自己的特殊需求

GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(Date.class,new JsonSerializer(){
            @Override
            public JsonElement serialize(Date date,Type type,

JsonSerializationContext jsonSerializationContext) {

                return new JsonPrimitive(date==null?0:date.getTime());
            }
        });
builder.create().toJson(map);