A way to send Direct Message to all Server Members? Java Discord Api

I wanted to script a command to send an Private Message to all Server Members, is that possible?
I know how to send a DM to the Author of the message but not to all Server Members.

Yes you can, suppose you have your target server's ID, with that you can call on your bot's jda instance

jda.getGuildById(<ID>);

Or if you just have the name, it's also possible with

jda.getGuildsByName(<NAME>, <CASE_SENSITIVE>)

The name one will return a list with all the matching names, this is quite impractical, since getting the ID is so easy.

You might have gotten your Guild object some other way (Through a listener maybe?), it does not matter.

Now you can either call guild.getMembers() or guild.getMemberCache() which one should you choose?
guild.getMemberCache() is, by default more efficient and in the end it implements the Iterable interface, so for all your intents and purposes, it should be better to use getMemberCache(), the benefit of getMembers() is that you'll get it as a list, making is trivial to do more processing.

Now you have your List<Member> or MemberCacheView, let's iterate through it
here the simplest option is the forEach() method, or just a for each loop:

for (Member member : guild.getMemberCache())

Or:

guild.getMemberCache().forEach(member -> <DO_SOMETHING>)

(If you choose to use guild.getMembers() it would be exactly the same)

Now to actually send your messages:

Remember we are iterating over Member objects, but JDA does not allow us to open private channels through that, so we need

PrivateChannel channel = member.getUser().openPrivateChannel().complete();

Note that here you need to either wait for the synchronous complete() and receive the PrivateChannel object normally, or you can pass a consumer to the queue method when opening the PrivateChannel, which will be executed as soon as the channel is available:

Consumer<PrivateChannel> messageSender = channel -> channel.sendMessage("Hey~~!").queue();
user.openPrivateChannel().queue(messageSender);

Or:

user.openPrivateChannel().queue(channel -> channel.sendMessage("Hey~~!").queue());

Now we have the channel and sending a message is simple

channel.sendMessage("Hey~~!").queue();

So putting it all together we get:

Guild guild; //Guild you got from a listener, or from the JDA pool

for(Member member : guild.getMemberCache()) { //Iterating over cached members in the guild
   User user = member.getUser(); //Converting the member object to a User

  user.openPrivateChannel().queue(channel->
             channel.sendMessage("Hey~~!").queue()); //Opening the channel and sending the message

   /*  Now you can optionally close the channel to remove it from the JDA's mapping */
   channel.close().queue();
}