【发布时间】：2015-08-21 19:15:00
【问题描述】：
我正在尝试创建一个 bukkit 插件，该插件将连接到 tcp 服务器并在事件触发时发送消息。
我已经具备了基础知识，但我缺少一些东西，而且我不知道从哪里开始。我可以看到该插件与服务器建立了连接，但随后引发错误并且没有发送任何消息。
我试图了解在事件发生时如何将字符串发送到 tcp 客户端。为了测试，我使用了玩家移动事件。
当我启动时，我在craftbukkit 服务器日志中看到以下内容：
Loading libraries, please wait...
[19:53:25 INFO]: Starting minecraft server version 1.7.10
[19:53:25 INFO]: Loading properties
[19:53:25 INFO]: Default game type: SURVIVAL
[19:53:25 INFO]: Generating keypair
[19:53:26 INFO]: Starting Minecraft server on *:25565
[19:53:26 INFO]: This server is running CraftBukkit version git-Bukkit-1.7.9-R0.2-20-g0b2ed13-b3108jnks (MC: 1.7.10) (Implementing API version 1.7.10-R0.1-SNAPSHOT)
[19:53:27 INFO]: [Compass] Loading Compass v0.1
[19:53:27 INFO]: Preparing level "world"
[19:53:27 INFO]: Preparing start region for level 0 (Seed: 7985848474339719790)
[19:53:27 WARN]: Could not get information about this CraftBukkit version; perhaps you are running a custom one?: FileNotFoundException
[19:53:28 INFO]: Preparing spawn area: 66%
[19:53:28 WARN]: Could not get latest artifact information: FileNotFoundException
[19:53:28 INFO]: Preparing start region for level 1 (Seed: 524789769407484853)
[19:53:29 INFO]: Preparing spawn area: 70%
[19:53:30 INFO]: Preparing start region for level 2 (Seed: 524789769407484853)
[19:53:30 INFO]: [Compass] Enabling Compass v0.1
[19:53:30 INFO]: [Compass] Start up.
[19:53:30 INFO]: [Compass] trying connect0
[19:53:30 INFO]: [Compass] getOutputStream()
[19:53:30 INFO]: [Compass] getInputStream()
[19:53:30 INFO]: Server permissions file permissions.yml is empty, ignoring it
[19:53:30 INFO]: Done (3.312s)! For help, type "help" or "?"
[19:54:25 INFO]: UUID of player MagicPixelPunk is 0322446d-6b92-4b63-af77-98d6739ec53b
[19:54:25 INFO]: MagicPixelPunk[/127.0.0.1:55376] logged in with entity id 206 at ([world] -164.16068813003193, 65.0, -141.0983355740641)
当我连接到 minecraft 客户端并移动播放器时，我在craftbukkit 服务器日志中看到以下错误：
21:52:01 INFO]: outToServer is null
21:52:01 INFO]: [CompassTask] writing to outToServer
21:52:01 INFO]: [CompassTask] Send failed: exception:
21:52:01 WARN]: java.lang.NullPointerException
21:52:01 WARN]: at compass.Compass.onMove(Compass.java:61)
java类Compass.java如下：
package compass;
import java.util.logging.Logger;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.command.CommandException;
import org.bukkit.entity.Player;
import org.bukkit.plugin.Plugin;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerMoveEvent;
import org.bukkit.scheduler.BukkitRunnable;
import java.io.IOException;
import java.util.concurrent.TimeoutException;
import java.lang.Exception;
import java.lang.Error;
import java.io.*;
import java.net.*;
public class Compass extends JavaPlugin implements Listener{
public static Logger log = Logger.getLogger("Minecraft");
public DataOutputStream outToServer;
public void onEnable() {
log.info("[Compass] Start up.");
String sentence;
String modifiedSentence;
BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
log.info("[Compass] trying connect0");
try{
Socket clientSocket = new Socket("localhost", 6789);
log.info("[Compass] getOutputStream()");
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
log.info("[Compass] getInputStream()");
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
}
catch (Exception e){
log.info("[Compass] Send failed: Exception: ");
e.printStackTrace();
}
getServer().getPluginManager().registerEvents(this, this);
}
public void onReload() {
log.info("[Compass] Server reloaded.");
}
public void onDisable() {
log.info("[Compass] Server stopping.");
}
@EventHandler
public void onMove(PlayerMoveEvent event) {
try{
if (outToServer == null) {
log.info("outToServer is null");
}
log.info("[CompassTask] writing to outToServer");
outToServer.writeBytes("test"+"\n");
log.info(" [x] Sent '" + "test" + "'");
}
catch (Exception e){
log.info("[CompassTask] Send failed: exception:");
e.printStackTrace();
}
catch (Error e){
log.info("[CompassTask] Send failed: error:");
e.printStackTrace();
}
}
}
当我尝试写入时，为什么 outToServer 为空有什么想法吗？
【问题讨论】：
-
我不认为你有 java 堆栈跟踪？或者这是你唯一的痕迹？就像添加 e.printStackTrace();到第 40 行的错误捕获。
-
outToServer.writeBytes("test"+"\n");顺便说一句，这就是您的代码失败的地方。
-
您还有一个任务计时器，您的程序说“错误：[Errno 10054] 现有连接被远程主机强行关闭”我猜这意味着它在任务完成之前关闭.
-
如上所述，更好的异常日志记录会更容易发现问题。在 catch 块中，将 e.getMessage() 包含在您的日志字符串中。或者只是 e.printStackTrace()。它应该更好地了解出了什么问题。
-
我更新了代码以使用 e.printStackTrace，堆栈跟踪现在显示在上面的日志中。