Java MySQL更新查询产生空指针异常_Java_Mysql_Sql_Nullpointerexception

Java MySQL更新查询产生空指针异常

java mysql sql

Java MySQL更新查询产生空指针异常,java,mysql,sql,nullpointerexception,Java,Mysql,Sql,Nullpointerexception,我有一个MySQL更新查询，当用户键入/preference命令时运行，但是我的MySQLPreparedStatementtry/catch正在创建一个NullPointerException 这里是更新的堆栈跟踪： [19:28:19] [Server thread/WARN]: java.lang.NullPointerException [19:28:19] [Server thread/WARN]: at net.coded.playerdata.cmds.Pardon.onCo

我有一个MySQL更新查询，当用户键入

/preference

命令时运行，但是我的MySQL

PreparedStatement

try/catch正在创建一个

NullPointerException

这里是更新的堆栈跟踪：

[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)

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;
    }
}

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;
            }

这是课程：

[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)

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;
    }
}

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;
            }

以下是导致问题的if语句：

[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)

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;
    }
}

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

中关闭连接。我还尝试在

try

之前声明

连接

，

准备语句

，以及查询字符串。我相当肯定这大部分代码都是有效的，因为我使用了MySQL和Java文档来编写这段代码。我肯定错过了什么。非常感谢您的帮助

它是

preparedStmt.setString（3，toUnban.getUniqueId（）.toString（））
根据您的评论，似乎toUnban
或toUnban.getUniqueId（）
是一个null
值。同样添加调试语句并再次运行以检查：
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
，请调查相应变量为什么为null
任何stacktrace？（请更新问题！不要将堆栈跟踪作为注释发布。）看到了。哪一行是preference.java:54
？Stacktrace并不总是必需的，只需指出哪一条语句产生了错误。@ADTC第54行似乎是：conn.close（）@swiftly你说的“似乎是”是什么意思？请查看源代码并检查第54行的语句。您应该能够看到左侧的行号（如果启用了此功能）或编辑器状态栏上的当前行号。另外，我非常怀疑它是conn.close（）
，因为conn.prepareStatement
在此之前被调用了几行，所以conn
不能null
。