从 MongoDB 中获取列表并将其插入数组列表时出现 NullPointer

Question

所以现在我正在尝试从 MongoDB 中检索一个 table，它目前只包含 1 个值。因此，每当我尝试从 Mongo 中提取数据并将其插入包含 ArrayList 的 ArrayList 或比较器散列图中时，它都会出于某种奇怪的原因输出 空指针 。我不确定为什么当 table 本身不为空时它会抛出 空指针 。错误

 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.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 行

 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提取所有数据并将其插入比较器

MongoToMap 方法

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 "long" 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();
}

或更改帐户：

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，但您从未对其进行初始化。

在这种情况下，除非您将有效的 List<String> 传递给 Account 构造函数，否则变量具有空值，但您的代码仅使用默认构造函数 (new Account())，因此该列表保持为空。

如果您的乘数是有效列表，则给定行中出现 NullPointerException 的唯一原因是您将无效（空）列表传递给 addMultiplier。

要找出异常的原因，您可以调试您的应用程序或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:)

从 MongoDB 中获取列表并将其插入数组列表时出现 NullPointer

NullPointer when grabbing a list from MongoDB and inserting it into an arraylist

java

arraylist

mongodb

bukkit