Java NoSuchFieldError when using Reflection, BukkitAPI - bukkit

Question

I`m trying to make packet (in bukkit API).However I get a NoSuchFieldException.
public class PacketPlayOutPlayerInfo {
private static final Class<?> packetClass = Reflections.getCraftClass("PacketPlayOutPlayerInfo");
private static final Class<?>[] typesClass = new Class<?>[]{ String.class, boolean.class, int.class };
private static int type = 0;
static {
try {
if (packetClass.getConstructor(typesClass) == null) {
type = 1;
}
} catch (Exception e) {
type = 1;
}
}
public static Object getPacket(String s, boolean b, int i) {
try {
if (type == 0) {
return packetClass.getConstructor(typesClass).newInstance(s, b, i);
}
else if (type == 1) {
Class<?> clazz = Reflections.getCraftClass("PacketPlayOutPlayerInfo");
Object packet = packetClass.getConstructor().newInstance();
Reflections.getPrivateField(clazz, "username").set(packet, s);
Reflections.getPrivateField(clazz, "gamemode").set(packet, 1);
Reflections.getPrivateField(clazz, "ping").set(packet, i);
Reflections.getPrivateField(clazz, "player").set(packet, new OfflineUser(s).getProfile());
if (!b) {
Reflections.getPrivateField(clazz, "action").set(packet, 4);
}
return packet;
}
} catch (Exception e) {
if (FunnyGuilds.exception(e.getCause())) {
e.printStackTrace();
}
}
return null;
}
}
Here`s full error:
[20:25:43] [IndependentThread/WARN]: java.lang.NoSuchFieldException: username
[20:25:43] [IndependentThread/WARN]: at java.lang.Class.getDeclaredField(Unknown Source)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.reflect.Reflections.getPrivateField(Reflections.java:123)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.reflect.transition.PacketPlayOutPlayerInfo.getPacket(PacketPlayOutPlayerInfo.java:31)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerListManager.packets(PlayerListManager.java:88)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerListManager.send(PlayerListManager.java:67)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerList.send(PlayerList.java:160)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerListManager.updatePlayers(PlayerListManager.java:24)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.thread.Action.execute(Action.java:37)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.thread.IndependentThread.execute(IndependentThread.java:43)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.thread.IndependentThread.run(IndependentThread.java:28)
[20:25:43] [IndependentThread/WARN]: java.lang.NullPointerException
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.reflect.transition.PacketPlayOutPlayerInfo.getPacket(PacketPlayOutPlayerInfo.java:31)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerListManager.packets(PlayerListManager.java:88)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerListManager.send(PlayerListManager.java:67)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerList.send(PlayerList.java:160)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.element.PlayerListManager.updatePlayers(PlayerListManager.java:24)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.thread.Action.execute(Action.java:37)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.thread.IndependentThread.execute(IndependentThread.java:43)
[20:25:43] [IndependentThread/WARN]: at net.dzikoysk.funnyguilds.util.thread.IndependentThread.run(IndependentThread.java:28)
PS: Sorry for my bad english.

Answer 1

The exception seems to be appropriate given that PacketPlayOutPlayerInfo does not define the fields you are attempting to access. Given the choice of field names, I gather that you might be trying to set values for PacketPlayOutPlayerInfo.PlayerInfoData; even so, its field names are obfuscated and must be given as such unless you pass the information as part of its constructor.
Since this question concerns itself with accessing de-compiled proprietary code, I will leave you with these suggestions:
Familiarize yourself with ProtocolLib, as it already does most of the heavy lifting when it comes to managing and tweaking packets.
If you still want to get your hands dirt and DIY, peruse ProtocolLib's source on GitHub.
If you want the nitty-gritty details about Minecraft classes, I suggest using Spigot's BuildTool, if you aren't already. A side effect of the build process are decompiled Minecraft classes (see work/decompileXXX/net/minecraft/server directory thereunder. This info will help you properly implement reflection calls to instantiate classes and modified fields.
In older versions of bukkitapi(1.6-1.7) this code works great.
To use ProtocolLib i must edit many of code. Thic exception is caused by this class or other?
PacketPlayOutPlayerInfo was changed in 1.8 and continues to change. I looked at the 1.8 (farthest I could go back) and 1.11.2 version and there is a world of difference. That is the problem working with classes that are not part of an API. They will change at will and no one will shed a tear if code breaks outside of Minecraft.
While ProtocolLib may also break, its knowledgeable and experienced developers will fix it quick. They must, since many plugins use it to avoid nasty surprises with new Minecraft releases. If ProtocolLib is not your cup of tea, then I suggest you use BuildTools, inspect the decompile class and adjust your code accordingly. Having Minecraft Modern a click away would also be a good thing.

Answer 2

I think you should check the requesting object variable names(your variable should be camel case). Because in api call you must request with the name exactly in api doc.