Java, bukkit plugin, throws errors

Question

I created this plugin but it says error and I do not know how to solve it, for each answer, thank you.

Plugin is when the command sends a message prefix a suffix setting is in a config.

Source:

package cz.denowq.flatrov;


import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.plugin.java.JavaPlugin;

public class flatrov extends JavaPlugin{
    
    @Override
    public void onEnable() {
        
        getLogger().info("[FlatRov] Načítávaní pluginu na verzi 1.0.1");
        
        getConfig().options().copyDefaults();
        saveConfig();
        
    }
    
    @Override
    public void onDisable() {
        
        getLogger().info("[FlatRov] Byl vypnut!");
        
    }
    
    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        
        Player player = (Player) sender;
        String text = "";
        if (player.hasPermission("flatrov.zprava")) {
            if (cmd.getName().equalsIgnoreCase("zprava")) {
                if((text = getConfig().getString("flatrav.zprava.prikaz")).length() != 0) {
                    String message = joinArgs(args);
                     Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', "" + getConfig().getString("flatrav.zprava.prefix") + " " + getConfig().getString("flatrav.zprava.suffix") + message));
                } else {
                    player.sendMessage(ChatColor.RED + " Použij /zprava <zprava> pro napsání zpravy!");
                }
            }
        } else {
            player.sendMessage(ChatColor.RED + " Nemáš povolený používat tento příkaz!");
        }
        return false;
    }
        
    private String joinArgs(String[] args) {
        String separator = ""; // empty on first iteration
        StringBuilder builder = new StringBuilder();
        for (String arg : args) {
            builder.append(separator).append(arg);
            separator = " "; // space after each arg
        }
        return builder.toString(); // return result
    }
    //String message = joinArgs(args);
}

Error:

[20:04:14] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'zprava' in plugin FlatRov v1.0.1
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot.jar:git-Spigot-1564]
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:181) ~[spigot.jar:git-Spigot-1564]
    at org.bukkit.craftbukkit.v1_7_R4.CraftServer.dispatchCommand(CraftServer.java:767) ~[spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PlayerConnection.handleCommand(PlayerConnection.java:1016) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PlayerConnection.a(PlayerConnection.java:846) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PacketPlayInChat.a(PacketPlayInChat.java:28) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PacketPlayInChat.handle(PacketPlayInChat.java:65) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.NetworkManager.a(NetworkManager.java:184) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.ServerConnection.c(ServerConnection.java:81) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.MinecraftServer.v(MinecraftServer.java:731) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.DedicatedServer.v(DedicatedServer.java:289) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.MinecraftServer.u(MinecraftServer.java:584) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:490) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [spigot.jar:git-Spigot-1564]
Caused by: java.lang.NullPointerException
    at cz.denowq.flatrov.flatrov.onCommand(flatrov.java:36) ~[?:?]
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot.jar:git-Spigot-1564]
    ... 13 more
[20:04:25] [Server thread/INFO]: DenOwq issued server command: /zprava test
[20:04:25] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'zprava' in plugin FlatRov v1.0.1
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot.jar:git-Spigot-1564]
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:181) ~[spigot.jar:git-Spigot-1564]
    at org.bukkit.craftbukkit.v1_7_R4.CraftServer.dispatchCommand(CraftServer.java:767) ~[spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PlayerConnection.handleCommand(PlayerConnection.java:1016) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PlayerConnection.a(PlayerConnection.java:846) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PacketPlayInChat.a(PacketPlayInChat.java:28) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.PacketPlayInChat.handle(PacketPlayInChat.java:65) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.NetworkManager.a(NetworkManager.java:184) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.ServerConnection.c(ServerConnection.java:81) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.MinecraftServer.v(MinecraftServer.java:731) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.DedicatedServer.v(DedicatedServer.java:289) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.MinecraftServer.u(MinecraftServer.java:584) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:490) [spigot.jar:git-Spigot-1564]
    at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [spigot.jar:git-Spigot-1564]
Caused by: java.lang.NullPointerException
    at cz.denowq.flatrov.flatrov.onCommand(flatrov.java:36) ~[?:?]
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot.jar:git-Spigot-1564]
    ... 13 more

EDIT: remove config

This looks like it is a highly specialized question that deals with interfacing with the Minecraft Bukkit plugin. Such questions I think are better suited for the Bukkit forums as opposed to here. Only thing I can suggest is to debug it in your development environment by setting up mock data and passing a command through to see where it errors. From the looks of it, you are not accounting for a case in which an exception is thrown, such as the player object not being extracted correctly. — ryanlutgen
– ryanlutgen, Commented Aug 3, 2014 at 19:07
(text = getConfig().getString("flatrav.zprava.prikaz")).length() appears to be causing the NPE, please make sure your config.yml file has a value associated with that key. — August
– August, Commented Aug 3, 2014 at 19:11
@Vizkos actually it's just an NPE that gets called from some internal methods. — CrypticStorm
– CrypticStorm, Commented Aug 3, 2014 at 19:34

CrypticStorm · Accepted Answer · 2014-08-03 19:33:50Z

1

Your stack trace shows an error on line 36. This is the line containing your first config call: getConfig().getString("flatrav.zprava.prikaz").

If your config does now contain a value at flatrav.zprava.prikaz, the method will return null. In Java, you can not run methods on a null value. You store this null as text which is perfectly fine, but the second you call .length() on that null value, you get a NullPointerException. To fix this, you should check if text == null or change getConfig().getString("flatrav.zprava.prikaz") to getConfig().getString("flatrav.zprava.prikaz", "") which will make the method return an empty string if it fails to find anything at " flatrav.zprava.prikaz".

answered Aug 3, 2014 at 19:33

CrypticStorm

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Comments

gyroninja · Accepted Answer · 2014-08-03 19:47:41Z

You seemed to have either learned bukkit 2 years ago or you are just using bad practices because around 2 years ago bukkit started automatically logging when your plugin was enabled or disabled.

You do not need to log that your plugin is enabled / disabled since bukkit already does that.

This code can be simplified

getConfig().options().copyDefaults();
saveConfig();

can be written as

saveDefaultConfig();

Next, in the command handler you shouldn't check for the permission there. You should add the permission node to the command in your plugin.yml

You should specify a default value when reading the configuration. Since the key doesn't exist it is returning null when you try accessing it with getString(). Use something like this instead.

getString("flatrav.zprava.prikaz"), "")

This method will return an empty string if it doesn't exist.

Also, your joinArgs() function appends an extra space to the output.

A quick fix to that after appending all the elements together use something like

sb.set length(sb.get length - 1);

Rishaan Gupta · Accepted Answer · 2015-04-23 08:12:18Z

There is also the problem here

@Override
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {

    Player player = (Player) sender;
    String text = "";

The problem is that you are immediately casting your sender to type Player without checking if the sender is a player. The problem will only show up if someone sends a command from the console or a plugin uses the server as a CommandSender when dispatching a command. To fix this just add an if statement that encompasses the rest of the method.

Also if you return false from the onCommand method the sender will receive a message from the server about incorrect/invalid usage of the command. Try returning true unless you want them to be sent this message

@Override
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {

    if (sender instanceof Player) {
        Player player = (Player) sender;
        String text = "";
        if (player.hasPermission("flatrov.zprava")) {
            if (cmd.getName().equalsIgnoreCase("zprava")) {
                if((text = getConfig().getString("flatrav.zprava.prikaz")).length() != 0) {
                    String message = joinArgs(args);
                    Bukkit.broadcastMessage(ChatColor.translateAlternateColorCodes('&', "" + getConfig().getString("flatrav.zprava.prefix") + " " + getConfig().getString("flatrav.zprava.suffix") + message));
                } else {
                    player.sendMessage(ChatColor.RED + " Použij /zprava <zprava> pro napsání zpravy!");
                }
            }
        } else {
            player.sendMessage(ChatColor.RED + " Nemáš povolený používat tento příkaz!");
        }
    }
    return true;
}

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