Why can this object not be serialized?

Question

Ok, for my Bukkit Plugin, I need the following java class (NewItem.java) to be serializable, but it is not. It gives me the error when my plugin tries to save it:

16:33:23 [SEVERE] java.io.NotSerializableException: org.bukkit.inventory.ItemSta
ck
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeObject0(Unknown Sourc
e)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeObject(Unknown Source
)
16:33:23 [SEVERE]       at java.util.ArrayList.writeObject(Unknown Source)
16:33:23 [SEVERE]       at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown
Source)
16:33:23 [SEVERE]       at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unkno
wn Source)
16:33:23 [SEVERE]       at java.lang.reflect.Method.invoke(Unknown Source)
16:33:23 [SEVERE]       at java.io.ObjectStreamClass.invokeWriteObject(Unknown S
ource)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeSerialData(Unknown So
urce)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeOrdinaryObject(Unknow
n Source)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeObject0(Unknown Sourc
e)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeObject(Unknown Source
)
16:33:23 [SEVERE]       at java.util.HashMap.writeObject(Unknown Source)
16:33:23 [SEVERE]       at sun.reflect.GeneratedMethodAccessor42.invoke(Unknown
Source)
16:33:23 [SEVERE]       at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unkno
wn Source)
16:33:23 [SEVERE]       at java.lang.reflect.Method.invoke(Unknown Source)
16:33:23 [SEVERE]       at java.io.ObjectStreamClass.invokeWriteObject(Unknown S
ource)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeSerialData(Unknown So
urce)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeOrdinaryObject(Unknow
n Source)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeObject0(Unknown Sourc
e)
16:33:23 [SEVERE]       at java.io.ObjectOutputStream.writeObject(Unknown Source
)
16:33:23 [SEVERE]       at com.tommy3244.plugins.MakeYourOwnBlocks.SaveLoadAPI.s
ave(SaveLoadAPI.java:16)
16:33:23 [SEVERE]       at com.tommy3244.plugins.MakeYourOwnBlocks.MakeYourOwnBl
ocks.onDisable(MakeYourOwnBlocks.java:60)
16:33:23 [SEVERE]       at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlug
in.java:219)
16:33:23 [SEVERE]       at org.bukkit.plugin.java.JavaPluginLoader.disablePlugin
(JavaPluginLoader.java:481)
16:33:23 [SEVERE]       at org.bukkit.plugin.SimplePluginManager.disablePlugin(S
implePluginManager.java:400)
16:33:23 [SEVERE]       at org.bukkit.plugin.SimplePluginManager.disablePlugins(
SimplePluginManager.java:393)
16:33:23 [SEVERE]       at org.bukkit.plugin.SimplePluginManager.clearPlugins(Si
mplePluginManager.java:434)
16:33:23 [SEVERE]       at org.bukkit.craftbukkit.v1_4_6.CraftServer.reload(Craf
tServer.java:563)
16:33:23 [SEVERE]       at org.bukkit.Bukkit.reload(Bukkit.java:184)
16:33:23 [SEVERE]       at org.bukkit.command.defaults.ReloadCommand.execute(Rel
oadCommand.java:23)
16:33:23 [SEVERE]       at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCo
mmandMap.java:186)
16:33:23 [SEVERE]       at org.bukkit.craftbukkit.v1_4_6.CraftServer.dispatchCom
mand(CraftServer.java:514)
16:33:23 [SEVERE]       at org.bukkit.craftbukkit.v1_4_6.CraftServer.dispatchSer
verCommand(CraftServer.java:506)
16:33:23 [SEVERE]       at net.minecraft.server.v1_4_6.DedicatedServer.al(Dedica
tedServer.java:260)
16:33:23 [SEVERE]       at net.minecraft.server.v1_4_6.DedicatedServer.r(Dedicat
edServer.java:225)
16:33:23 [SEVERE]       at net.minecraft.server.v1_4_6.MinecraftServer.q(Minecra
ftServer.java:494)
16:33:23 [SEVERE]       at net.minecraft.server.v1_4_6.MinecraftServer.run(Minec
raftServer.java:427)
16:33:23 [SEVERE]       at net.minecraft.server.v1_4_6.ThreadServerApplication.r
un(SourceFile:849)

The source code for the NewItem.java is here:

package com.tommy3244.plugins.MakeYourOwnBlocks;

import java.util.*;
import java.util.logging.Logger;
import java.io.Serializable;
import org.bukkit.Bukkit;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.configuration.ConfigurationSection;
import org.bukkit.entity.Player;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.ShapedRecipe;

public class NewItem implements Serializable
{
   public int id;
 public byte data;
  public int damage;
 public String name;
    public List<String> lore;
    public List<List<String>> commands;
    public NewItem(List<String> lore, String name, int itemid, byte itemdata, List<List<String>> lines, int damage, boolean hasRecipe, ConfigurationSection section)
 {
      id = itemid;
       data = itemdata;
       this.name = name;
      this.damage = damage;
      this.lore = lore;
      commands = lines;
      ItemStack stack;
       if(data != 0)
      {
          stack = new ItemStack(id, data);
       }
      else
       {
          stack = new ItemStack(id);
     }
      if(hasRecipe)
      {
      try
        {
      ShapedRecipe recipe = new ShapedRecipe(stack);
     String r1 = section.getString("items."+name+".r1");
        String r2 = section.getString("items."+name+".r2");
        String r3 = section.getString("items."+name+".r3");
        List<Integer> defines = section.getIntegerList("items."+name+".defines");
        Character[] chars = {'1', '2', '3', '4', '5', '6', '7', '8', '9'};
     List<Character> charlist = Arrays.asList(chars);
     for(int defined : defines)
     {
          Material md = Material.getMaterial(defined);
           
           recipe.setIngredient(charlist.get(0), md);
     }
      String[] rows = {r1, r2, r3};
      recipe.shape(rows);
        Bukkit.addRecipe(recipe);
      }
      catch(Exception error)
     {
          
       }
      }
  }
  public NewItem(List<String> lore, String name, int itemid, List<List<String>> lines, int damage, boolean hasRecipe, ConfigurationSection section)
    {
      this(lore, name, itemid, (byte)0, lines, damage, hasRecipe, section);
  }
  public Logger getLogger()
  {
      return Bukkit.getServer().getPluginManager().getPlugin("MakeYourOwnBlocks").getLogger();
 }
  public int getItem()
   {
      return id;
 }
  public String getName()
    {
      return name;
   }
  public boolean onRightClick(Player p, boolean right, boolean block)
    {
      int isright; 
      int isblock;
       if(right)
      {
          isright = 1;
       }
      else
       {
          isright = 0;
       }
      if(block)
      {
          isblock = 1;
       }
      else
       {
          isblock = 0;
       }
      try
        {
          List<String> cmds = commands.get(0);
         for(String line : cmds)
            {
              line = line.replaceAll("\\<block\\>", String.valueOf(isblock));
                line = line.replaceAll("\\<right\\>", String.valueOf(isright));
                String[] segments = line.split(" ");
             String cmd = segments[0];
              List<String> rest = Arrays.asList(segments);
             getLogger().info(String.valueOf(rest));
                rest.remove(0);
                StringBuilder sb = new StringBuilder();
                for(String stst : rest)
                {
                  sb.append(stst);
               }
              String reststr = sb.toString();
                if(cmd.equalsIgnoreCase("cmd"))
              {
                  Bukkit.getServer().dispatchCommand(Bukkit.getConsoleSender(), reststr);
                }
              if(cmd.equalsIgnoreCase("setblock"))
             {
                  Block b = p.getWorld().getBlockAt(Integer.parseInt(rest.get(0)), Integer.parseInt(rest.get(1)), Integer.parseInt(rest.get(2)));
                    b.setTypeId(Integer.parseInt(rest.get(3)));
                    if(rest.size() > 4)
                 {
                      b.setData((byte)Integer.parseInt(rest.get(5)));
                    }
              }
              if(cmd.equalsIgnoreCase("say"))
              {
                  p.sendMessage(reststr);
                }
              if(cmd.equalsIgnoreCase("kill"))
             {
                  p.setHealth(0);
                }
              if(cmd.equalsIgnoreCase("hurt"))
             {
                  p.setHealth(p.getHealth()-Integer.parseInt(rest.get(0)));
              }
          }
      }
      catch(Exception error)
     {
          error.printStackTrace();
           return false;
      }
      return true;
   }
  public boolean onLeftClick(Player p, boolean right, boolean block)
 {
      int isright; 
      int isblock;
       if(right)
      {
          isright = 1;
       }
      else
       {
          isright = 0;
       }
      if(block)
      {
          isblock = 1;
       }
      else
       {
          isblock = 0;
       }
      try
        {
          List<String> cmds = commands.get(1);
         for(String line : cmds)
            {
              line.replaceAll("\\<block\\>", String.valueOf(isblock));
               line.replaceAll("\\<right\\>", String.valueOf(isright));
               String[] segments = line.split(" ");
             String cmd = segments[0];
              List<String> rest = Arrays.asList(segments);
             rest.remove(rest.get(0));
              StringBuilder sb = new StringBuilder();
                for(String stst : rest)
                {
                  sb.append(stst);
               }
              String reststr = sb.toString();
                if(cmd.equalsIgnoreCase("cmd"))
              {
                  Bukkit.getServer().dispatchCommand(Bukkit.getConsoleSender(), reststr);
                }
              if(cmd.equalsIgnoreCase("setblock"))
             {
                  Block b = p.getWorld().getBlockAt(Integer.parseInt(rest.get(0)), Integer.parseInt(rest.get(1)), Integer.parseInt(rest.get(2)));
                    b.setTypeId(Integer.parseInt(rest.get(3)));
                    if(rest.size() > 4)
                 {
                      b.setData((byte)Integer.parseInt(rest.get(5)));
                    }
              }
              if(cmd.equalsIgnoreCase("say"))
              {
                  p.sendMessage(reststr);
                }
              if(cmd.equalsIgnoreCase("kill"))
             {
                  p.setHealth(0);
                }
              if(cmd.equalsIgnoreCase("hurt"))
             {
                  p.setHealth(p.getHealth()-Integer.parseInt(rest.get(0)));
              }
          }
      }
      catch(Exception error)
     {
          return false;
      }
      return true;
   }
}

Answer 1

You need to implement java.io.Serializable :

public class NewItem implements Serializable

From JavaDoc:

Serializability of a class is enabled by the class implementing the java.io.Serializable interface. Classes that do not implement this interface will not have any of their state serialized or deserialized. All subtypes of a serializable class are themselves serializable. The serialization interface has no methods or fields and serves only to identify the semantics of being serializable.

Answer 2

通过实现Serializable接口将其标记为Serializable

Answer 3

You use some List s. List does not implement Serializable . [Not all List -implementations may be Serializable ]

I would try to use ArrayList which implements Serializable .

Of cause NewItem must also implement Serializable .