java - MySQL更新查询产生空指针异常

Question

我有一个 MySQL 更新查询，当用户键入 /pardon 命令时运行，但我的 MySQL PreparedStatement try/catch 正在创建一个 NullPointerException.

这是更新的堆栈跟踪:

[19:28:19] [Server thread/WARN]: java.lang.NullPointerException
[19:28:19] [Server thread/WARN]:    at net.coded.playerdata.cmds.Pardon.onCommand(Pardon.java:50)
[19:28:19] [Server thread/WARN]:    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
[19:28:19] [Server thread/WARN]:    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:180)
[19:28:19] [Server thread/WARN]:    at org.bukkit.craftbukkit.v1_7_R3.CraftServer.dispatchCommand(CraftServer.java:703)
[19:28:19] [Server thread/WARN]:    at org.bukkit.craftbukkit.v1_7_R3.CraftServer.dispatchServerCommand(CraftServer.java:690)
[19:28:19] [Server thread/WARN]:    at net.minecraft.server.v1_7_R3.DedicatedServer.aB(DedicatedServer.java:296)
[19:28:19] [Server thread/WARN]:    at net.minecraft.server.v1_7_R3.DedicatedServer.v(DedicatedServer.java:261)
[19:28:19] [Server thread/WARN]:    at net.minecraft.server.v1_7_R3.MinecraftServer.u(MinecraftServer.java:558)
[19:28:19] [Server thread/WARN]:    at net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:469)
[19:28:19] [Server thread/WARN]:    at net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628)

这是类(class):

public class Pardon implements CommandExecutor {

    @SuppressWarnings("deprecation")
    public boolean onCommand(CommandSender sender, Command cmd, String commandLabel, String[] args) {

        if (cmd.getName().equalsIgnoreCase("pardon")) {

            if (!sender.hasPermission("bukkit.command.unban.player") || (!sender.isOp())) {
                MessageManager.getInstance().severe(sender, ChatColor.RED + "You do not have permission to do that.");
                return true;
            }

            if (args.length == 0) {
                MessageManager.getInstance().severe(sender, "You must specify a player name!");
                return true;
            }

            if (args.length >= 1) {
                //Unban the player when they are offline
                Bukkit.getOfflinePlayer(args[0]).setBanned(false);
                Player toUnban = Bukkit.getPlayer(args[0]);

                // Update database
                try {
                    Class.forName(PlayerData.driver).newInstance();
                    Connection conn = DriverManager.getConnection(PlayerData.url + PlayerData.dbName, PlayerData.userName, PlayerData.password);

                    String query = "UPDATE playerdata SET banned = ?, ban_reason = ? WHERE uuid = ?";

                    // create the MySQL insert preparedstatement
                    PreparedStatement preparedStmt = conn.prepareStatement(query);
                    preparedStmt.setInt(1, 0);
                    preparedStmt.setString(2, null);
                    preparedStmt.setString(3, toUnban.getUniqueId().toString());

                    // execute the preparedstatement
                    preparedStmt.executeUpdate();
                    conn.close();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }

                Command.broadcastCommandMessage(sender, ChatColor.GREEN + "Player " + ChatColor.WHITE + args[0] + ChatColor.GREEN + " has been unbanned.");
                return true;
            }
        }
        return true;
    }
}

以下是导致问题的 if 语句:

if (args.length >= 1) {
                //Unban the player when they are offline
                Bukkit.getOfflinePlayer(args[0]).setBanned(false);
                Player toUnban = Bukkit.getPlayer(args[0]);

                // Update database
                try {
                    Class.forName(PlayerData.driver).newInstance();
                    Connection conn = DriverManager.getConnection(PlayerData.url + PlayerData.dbName, PlayerData.userName, PlayerData.password);

                    String query = "UPDATE playerdata SET banned = ?, ban_reason = ? WHERE uuid = ?";

                    // create the MySQL insert preparedstatement
                    PreparedStatement preparedStmt = conn.prepareStatement(query);
                    preparedStmt.setInt(1, 0);
                    preparedStmt.setString(2, null);
                    preparedStmt.setString(3, toUnban.getUniqueId().toString());

                    // execute the preparedstatement
                    preparedStmt.executeUpdate();
                    conn.close();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }

                Command.broadcastCommandMessage(sender, ChatColor.GREEN + "Player " + ChatColor.WHITE + args[0] + ChatColor.GREEN + " has been unbanned.");
                return true;
            }

我尝试为语句/查询创建一个单独的方法，添加一个finally子句来关闭连接，而不是在try中关闭它们。我还尝试在 try 之前声明 Connection、PreparedStatement 和查询字符串。我相当确定这大部分是有效的代码，因为我使用 MySQL 和 Java 文档来编写此代码。我一定错过了一些东西。非常感谢任何帮助!

Answer 1

it is preparedStmt.setString(3, toUnban.getUniqueId().toString());

根据您的评论，toUnban 或 toUnban.getUniqueId() 似乎是 null 值。同样添加调试语句并再次运行检查:

preparedStmt.setString(2, null);
System.out.println("toUnban null? " + (toUnban==null));
System.out.println("toUnban.getUniqueId() null? " + (toUnban.getUniqueId()==null));
preparedStmt.setString(3, toUnban.getUniqueId().toString());

如果任一调试输出状态为 true，请调查相应变量为何为 null。