NullPointerException和参数索引超出范围使用MySQL和PreparedStatement的异常

Question

我使用MySQL时出现这个错误，但无法弄清楚如何解决它。自从我从Connection.execute[whatever]()切换到PreparedStatement后，我一直在收到此错误，但似乎无法解决此问题。

的NullPointerException：

guild info space 
[09:51:56 WARN]: java.lang.NullPointerException 
[09:51:56 WARN]: at net.aspace.guilds.Guild.getGuild(Guild.java:56) 
[09:51:56 WARN]: at net.aspace.guilds.command.GuildsInfoCommand.execute(GuildsInfoCommand.java:28) 
[09:51:56 WARN]: at net.aspace.command.CommandNode.onCommand(CommandNode.java:64) 
[09:51:56 WARN]: at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) 
[09:51:56 WARN]: at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:140) 
[09:51:56 WARN]: at org.bukkit.craftbukkit.v1_10_R1.CraftServer.dispatchCommand(CraftServer.java:646) 
[09:51:56 WARN]: at org.bukkit.craftbukkit.v1_10_R1.CraftServer.dispatchServerCommand(CraftServer.java:632) 
[09:51:56 WARN]: at net.minecraft.server.v1_10_R1.DedicatedServer.aL(DedicatedServer.java:438) 
[09:51:56 WARN]: at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:401) 
[09:51:56 WARN]: at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:668) 
[09:51:56 WARN]: at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:567) 
[09:51:56 WARN]: at java.lang.Thread.run(Thread.java:745) 
[09:51:56 INFO]: Guild space does not exist! 

参数索引超出范围的异常：

java.sql.SQLException: Parameter index out of range (1 > number of parameters, which is 0). 
[11:11:37 WARN]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:963) 
[11:11:37 WARN]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896) 
[11:11:37 WARN]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885) 
[11:11:37 WARN]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860) 
[11:11:37 WARN]: at com.mysql.jdbc.PreparedStatement.checkBounds(PreparedStatement.java:3321) 
[11:11:37 WARN]: at com.mysql.jdbc.PreparedStatement.setInternal(PreparedStatement.java:3306) 
[11:11:37 WARN]: at com.mysql.jdbc.PreparedStatement.setString(PreparedStatement.java:4021) 
[11:11:37 WARN]: at net.aspace.guilds.Guild.getGuild(Guild.java:57) 
[11:11:37 WARN]: at net.aspace.guilds.command.GuildsInfoCommand.execute(GuildsInfoCommand.java:28) 

这里是Guild类：

package net.aspace.guilds; 

import java.sql.PreparedStatement; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.sql.Statement; 
import java.util.ArrayList; 
import java.util.List; 
import java.util.logging.Logger; 

import net.aspace.chat.Message; 
import net.aspace.guilds.GuildsPlugin; 
import net.aspace.guilds.util.MySQL; 
import net.aspace.util.SimpleCallback; 

import org.bukkit.entity.Player; 
import org.bukkit.plugin.Plugin; 
import org.bukkit.scheduler.BukkitRunnable; 
import org.bukkit.scheduler.BukkitTask; 

public class Guild { 

    public String name; 
    public List<String> members; 
    public int maxPlayers = 3; 

    public Guild(String name) { 
    } 

    public Guild(String name, List<String> members, int maxPlayers) { 
     this.name = name; 
     this.members = members; 
     this.maxPlayers = maxPlayers; 
    } 

    public void addPlayer(final Player p) { 
     final String gName = this.name; 
     new BukkitRunnable() { 

      public void run() { 
       try { 
        PreparedStatement ps = MySQL.getConnection() 
          .prepareStatement("UPDATE PlayerData SET GUILD='?' WHERE PLAYERNAME='?'"); 
        ps.setString(1, gName); 
        ps.setString(2, p.getName()); 
        ps.executeUpdate(); 
       } catch (SQLException e) { 
        e.printStackTrace(); 
       } 
      } 
     }.runTaskAsynchronously((Plugin) GuildsPlugin.getInstance()); 
    } 

    public static void getGuild(final String name, final SimpleCallback<Guild> callback) { 
     try { 
      PreparedStatement ps = MySQL.getConnection().prepareStatement("SELECT * FROM Guilds WHERE GUILD_NAME='?'"); 
      ps.setString(1, name); 
      ArrayList<String> players = new ArrayList<String>(); 

      ResultSet set = ps.executeQuery(); 
      if (set.next()) { 
       String gName = set.getString("GUILD_NAME"); 
       int maxMembers = set.getInt("MAX_MEMBERS"); 
       try { 
        PreparedStatement ps2 = MySQL.getConnection() 
          .prepareStatement("SELECT * FROM PlayerData WHERE GUILD = '?'"); 
        ps2.setString(1, name); 
        ResultSet result = ps2.executeQuery(); 
        GuildsPlugin.getInstance().getLogger().info("select"); 
        while (result.next()) { 
         players.add(result.getString("PLAYERNAME")); 
        } 
        result.close(); 
        callback.execute(new Guild(gName, players, maxMembers)); 
       } catch (SQLException e) { 
        e.printStackTrace(); 
       } 
       set.close(); 

      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
      callback.execute(null); 
     } catch (NullPointerException e) { 
      e.printStackTrace(); 
      callback.execute(null); 
     } 
    } 

    public static void createGuild(final Player p, final String name) { 
     new BukkitRunnable() { 

      @Override 
      public void run() { 
       try { 
       PreparedStatement ps = MySQL.getConnection().prepareStatement("SELECT * FROM PlayerData WHERE PLAYER_NAME = '?'"); 
       ps.setString(1,p.getName()); 



        //Get player data 
        ResultSet result = ps.executeQuery(); 
        if (result.first()) { 
         //Check if player is in a guild 
         if (result.getString("GUILD") == null) { 
          // TODO Check if guild exists 
          try { 
           //Add guild 
           PreparedStatement ps2 = MySQL.getConnection().prepareStatement("INSERT INTO Guilds (GUILD_NAME,MAX_MEMBERS) VALUES ('?',10)"); 
           ps2.setString(1,name); 
           ps2.executeUpdate(); 
           //Add player to guild 
           PreparedStatement ps3 = MySQL.getConnection().prepareStatement("UPDATE PlayerData SET GUILD='?'" 
             + "WHERE PLAYER_NAME='?'"); 
           ps3.setString(1,name); 
           ps3.setString(2,p.getName()); 
           p.sendMessage(Message.fromString(String.format("&eYou have created and joined the guild &b%s&e!",name))); 
          } catch (SQLException e) { 
           e.printStackTrace(); 
          } 
         } else { 
          //Player is in a guild 
          p.sendMessage(Message.fromString("&cYou are already in a guild!")); 
         } 
        } 
       } catch (SQLException e1) { 
        e1.printStackTrace(); 
       } 
      } 
     }.runTaskAsynchronously(GuildsPlugin.getInstance()); 
    } 

} 

这里是GuildInfoCommand类：

package net.aspace.guilds.command; 

import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.sql.Statement; 

import org.bukkit.command.CommandSender; 
import org.bukkit.entity.Player; 
import org.bukkit.plugin.Plugin; 

import net.aspace.chat.Message; 
import net.aspace.command.CommandNode; 
import net.aspace.guilds.Guild; 
import net.aspace.guilds.GuildsPlugin; 
import net.aspace.guilds.util.GuildsPlayer; 
import net.aspace.util.SimpleCallback; 

public class GuildsInfoCommand<E extends Plugin> extends CommandNode<E> { 

    public GuildsInfoCommand(E plugin) { 
     super(plugin); 
     // TODO Auto-generated constructor stub 
    } 

    @Override 
    public boolean execute(CommandSender sender, String... args) { 
     if (args.length >= 1) { 
      Guild.getGuild(args[0], new SimpleCallback<Guild>() { 

       @Override 
       public void execute(Guild guild) { 
        if (guild != null) { 

         sender.sendMessage(Message.fromString("&b&lGUILD INFO")); 
         sender.sendMessage(Message.fromString("&eGuild name: " + guild.name)); 
         sender.sendMessage(Message.fromString("&eGuild maxmembers: " + guild.maxPlayers)); 
         sender.sendMessage(
           Message.fromString("&eGuild members &7(" + Integer.toString(guild.members.size()) + "/" 
             + Integer.toString(guild.maxPlayers) + ")&e: ")); 
         guild.members.forEach(s -> { 
          sender.sendMessage(Message.fromString("&7- " + s)); 
         }); 
         sender.sendMessage(Message.fromString("&b&lGUILD INFO")); 

        } else { 
         sender.sendMessage(Message.fromString(String.format("&cGuild &e%s&c does not exist!", args[0]))); 
        } 

       } 
      }); 

     } else { 
      if (sender instanceof Player) { 
       Player player = (Player) sender; 
       GuildsPlayer player2 = GuildsPlayer.getPlayer(player); 
       player2.inGuild(new SimpleCallback<Boolean>() { 

        @Override 
        public void execute(Boolean response) { 
         if (response) { 
          Guild.getGuild(args[0], new SimpleCallback<Guild>() { 

           @Override 
           public void execute(Guild guild) { 
            if (guild != null) { 
             sender.sendMessage(Message.fromString("&b&lGUILD INFO")); 
             sender.sendMessage(Message.fromString("&eGuild name: &b" + guild.name)); 
             sender.sendMessage(Message.fromString("&eMember Limit: &b" + guild.maxPlayers)); 
             sender.sendMessage(Message.fromString(
               "&eGuild members &7(" + Integer.toString(guild.members.size()) + "/" 
                 + Integer.toString(guild.maxPlayers) + ")&e: ")); 
             guild.members.forEach(s -> { 
              sender.sendMessage(Message.fromString("&7- " + s)); 
             }); 
             sender.sendMessage(Message.fromString("&b&lGUILD INFO")); 

            } else { 
             sender.sendMessage(Message.fromString("&cYou are not in a guild!")); 
            } 
           } 

          }); 
         } else { 

         } 
        } 
       }); 
      } else { 
       sender.sendMessage(Message.fromString("&cYou must specify a guild name!")); 
      } 
     } 

     return true; 
    } 

    @Override 
    public String getName() { 
     // TODO Auto-generated method stub 
     return "info"; 
    } 

} 

代码MySQL类：

package net.aspace.guilds.util; 

import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.SQLException; 

import org.bukkit.Bukkit; 
import org.bukkit.command.ConsoleCommandSender; 

public class MySQL { 

    public static String host = "****"; 
    public static String port = "****"; 
    public static String database = "****"; 
    public static String username = "****"; 
    public static String password = "****"; 
    public static Connection con; 

    static ConsoleCommandSender console = Bukkit.getConsoleSender(); 

    // connect 
    public static void connect() { 
     if (!isConnected()) { 
      try { 
       con = DriverManager.getConnection("jdbc:mysql://" + host + ":" + port + "/" + database, username, password); 
       console.sendMessage("\247c[\2476Minepedia-System\247c] \247bMySQL-Verbindung wurde aufgebaut!"); 
      } catch (SQLException e) { 
       e.printStackTrace(); 
      } 
     } 
    } 

    // disconnect 
    public static void disconnect() { 
     if (isConnected()) { 
      try { 
       con.close(); 
       console.sendMessage("\247c[\2476Minepedia-System\247c]\247bMySQL-Verbindung wurde geschlossen!"); 
      } catch (SQLException e) { 
       e.printStackTrace(); 
      } 
     } 
    } 

    // isConnected 
    public static boolean isConnected() { 
     return (con == null ? false : true); 
    } 

    // getConnection 
    public static Connection getConnection() { 
     return con; 
    } 
} 

Answer 1

您需要调用MySQL.connect()方法尝试调用MySQL.getConnection()之前。

当你调用MySQL.getConnection()方法，无需MySQL.connect()方法，你没有创建连接，并且因此得到了NullPointerException在尝试调用MySQL.getConnection().prepareStatement...

您需要删除'字符，因为SQL解析器解释他们喜欢的字符串值，忽略占位符?。

例如：

PreparedStatement ps = 
    MySQL.getConnection().prepareStatement("SELECT * FROM Guilds WHERE GUILD_NAME=?");