NullPointer从MongoDB获取列表并将其插入数组列表时

Question

因此，到目前为止，我正试图从MongoDB检索一个表，该表目前只包含1个值。因此，每当我试图从Mongo中提取数据并将其插入包含ArrayList的ArrayList或比较器hashmap中时，它就会出于某种奇怪的原因输出空指针。我不太清楚为什么它要抛出空指针，而该表本身甚至都不是空的。

 Caused by: java.lang.NullPointerException
    at krimsonlib.account.Account.addMultiplier(Account.java:538) ~[?:?]
    at krimsonlib.account.AccountManager.MongoTOMap(AccountManager.java:169) ~[?:?]
    at krimsonlib.account.AccountManager.makeProfile(AccountManager.java:61) ~[?:?]
    at krimsonlib.core.join(core.java:37) ~[?:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_66]
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_66]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_66]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_66]
    at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[spigot-1.8.7-
    ... 14 more

这是将列表添加到现有列表的比较器方法。

第538项

 List<String> multipliers;

//comparator
  public Account(String id, String uuid, String name, String kingdom, String rank, String recruit, String joinDate, String lastOnline, List<String> multipliers, List<String> friends,int favor, int playtime, int crystals, int coins, int networklevel, int networkexp, List<String> achievements, List<String> pets, List<String> gadgets, List<String> particles, List<String> cloaking, List<String> clothing){
        this.id = id;
        this.uuid = uuid;
        this.name = name;
        this.kingdom = kingdom;
        this.rank = rank;
        this.recruit = recruit;
        this.joinDate = joinDate;
        this.lastOnline = lastOnline;
        this.multipliers = multipliers;
        this.friends = friends;
        this.favor = favor;
        this.playTime = playtime;
        this.crystals = crystals;
        this.coins = coins;
        this.networklevel = networklevel;
        this.networkexp = networkexp;
        this.achievements = achievements;
        this.pets = pets;
        this.gadgets = gadgets;
        this.particles = particles;
        this.cloaking = cloaking;
        this.clothing = clothing;
    }


public void newAccount(){
        UtilMap.account.put(uuid, new Account(getID(), getUUID(), getName(), getKingdom(), getRank(), getRecruit(), getJoinDate(), getLastOnline(), getMultipliers(), getFriends(), getFavor(), getPlayTime(), getCrystals(), getCoins(), getLevel(), getExp(), getAchievements(), getPets(), getGadgets(), getParticles(), getCloaking(), getClothing()));
    }
 public void addMultiplier(List<String> multipliers) {
            this.multipliers.addAll(multipliers); // this is line 538
        }

此方法从该特定用户中提取所有数据，并将其插入比较器。

MongoToMap法

public static void MongoTOMap(UUID uuid){
    String trim = uuid.toString().replace("-", "");
    String nontrim = uuid.toString();
    Account ac = new Account();
    DBObject r = new BasicDBObject("uuid", nontrim);
    DBObject found = Mongo.users.findOne(r);

    if ( found != null ){
        ac.setID((String) found.get("_id"));
        ac.setUUID((String) found.get("trimuuid"));
        ac.setName((String) found.get("name"));
        ac.setKingdom((String) found.get("Kingdom"));
        ac.setRecruit((String) found.get("recruit"));
        ac.setCrystals((int) found.get("crystals"));
        ac.setCoins((int) found.get("coins"));
        ac.setRank((String) found.get("rank"));
        ac.setFavor((int) found.get("favor"));
        ac.setJoinDate((String) found.get("First_Join_Date"));
        ac.setLastOnline((String) found.get("Last_Join_Date"));
        ac.addPlayTime((int) found.get("Playtime"));
        ac.setLevel((int) found.get("Network_Level"));
        ac.setExp((int) found.get("Network_Exp"));
        ac.addMultiplier((List) found.get("Multipliers"));
        ac.addFriend((List) found.get("friends"));
        ac.addAchievement((List) found.get("achievements"));
        ac.addPet((List) found.get("pets"));
        ac.addGadget((List) found.get("gadgets"));
        ac.addParticle((List) found.get("particles"));
        ac.addCloak((List) found.get("cloaking"));
        ac.addClothes((List) found.get("clothing"));

        ac.newAccount();
        System.out.println("[Mongo]- Converted user `" + UtilMap.account.get(trim).getName() + "` data to Map, Method/MongoTOMap #" + UtilMath.genReceipt());
    } else {
        //this error should NEVER occur
    }
}

Answer 1

您可能需要使用帐户的“长”构造函数：

if (found != null) {
    Account ac = new Account(
        (String) found.get("_id"),
        (String) found.get("trimuuid"),
        ... ,
        (List) found.get("Multipliers"),
        ...
    );
    ac.newAccount();
}

或变更帐户：

public void addMultiplier(List<String> multipliers) {
    if (this.multipliers != null) {
        this.multipliers.addAll(multipliers);
    } else {
        this.multipliers = multipliers;
    }
}

Answer 2

您正在声明变量multipliers，但从未初始化它。

在这种情况下，变量有一个空值，除非您将一个有效的List<String>传递给您的Account构造函数，但是您的代码只使用默认构造函数(new Account())，因此列表保持为空。

如果乘法器是有效的列表，那么在给定行中使用NullPointerException的唯一原因是将无效(null)列表传递给addMultiplier。

要找出异常的原因，可以调试应用程序，也可以添加这样的日志记录：

public void addMultiplier(List<String> multipliers) {
    if(this.multipliers == null)
    {
        System.out.println("this.multipliers is not set correctly");
    }
    if(multipliers == null)
    {
        System.out.println("parameter multipliers is not set correctly");
    }
    this.multipliers.addAll(multipliers); 
}

编辑:哦，我太慢了