Unban command JDA 4.1.1_101, can't make it work and I don't know why - bots

Question

i'm coding a Discord bot with JDA 4.1.1_101. I created the "ban" command, but i can't make the unban command work. I can't really understand why... Thank you for your help.
if (args[0].equalsIgnoreCase(Main.prefix + "unban")) {
if(event.getGuild().getSelfMember().hasPermission(Permission.BAN_MEMBERS)) {
if (args.length > 0 && args.length < 3) {
try {
event.getMessage().delete().queue();
User member = event.getMessage().getMentionedMembers().get(0).getUser();
String id = member.getId();
event.getGuild().unban(id).queue();
EmbedBuilder ban = new EmbedBuilder();
ban.setColor(Color.GREEN);
ban.setTitle("UnBan");
ban.setDescription("UnBan Report");
ban.addField("Staffer: ", event.getMessage().getAuthor().getName(), true);
ban.addField("Unban: ", member.getName(), true);
logs.sendMessage(ban.build()).queue();
} catch (IndexOutOfBoundsException exx) {
EmbedBuilder error = new EmbedBuilder();
error.setColor(0xff3923);
error.setTitle("Error: User");
error.setDescription("Invalid user.");
event.getChannel().sendMessage(error.build()).queue(message -> {
message.delete().queueAfter(5, TimeUnit.SECONDS);
});
}
} else {
EmbedBuilder error = new EmbedBuilder();
error.setColor(0xff3923);
error.setTitle("Error: Wrong usage.");
error.setDescription("Use: .unban [#user].");
event.getChannel().sendMessage(error.build()).queue(message -> {
message.delete().queueAfter(5, TimeUnit.SECONDS);
});
}
}
}

Answer 1

The problem is, that you are trying to retrieve the user from the mention in the message.
Since the user isn't part of the guild anymore, it seems like this doesn't work.
In order to work around this issue, you have to retrieve the ID manually.
A mention is always in the format <#userid> or <!#userid>.
To get the ID you could just split the message and replace the unnecessary parts, e.g. String id = event.getMessage().getContentRaw().split("<")[1].split(">")[0].replace("!", "").replace("#", "");
I'm sure there are better and smoother ways for doing this. ;)
A better way of retrieving the ID would be using a regex such as <#!?(\d+)> as mentioned by Minn.
In order to get the name of the user, you just need the ID via event.getJDA().getUserById(id).getName().
It's important to mention that you can't properly mention a user who isn't on the server (which is the case when they are banned).
(Addition: I tried using .getMentionedUsers() with the same result as OP.)