I have created a simple Java chat program, which provides one server and multiple clients.
But I only can make it where all clients can talk (the messages was sent to all clients).
I need to make a private chat beside the public chat I've made.
E.g: computerA just wants to chat with computerB, but computerA still can talk with all clients. How can I do this?
The easiest way to do it is to modify your protocol a little bit to include some information whether the message you are sending is a public (everyone can see it) or a private one (just user A and user B talking).
With that information in hand, in the server, whenever you find a private message, just send it to the one and only destination expecting that message. Do not try to do some peer to peer stuff because you will encounter many problems along the way.
Other small variation of this solution would be supporting "private rooms" on your chat server. But that will be a little bit more complicated to implement.
Related
I use this sample: 16.proactive-messages - as the base for my bot and it works fine, but I'd like to extend it, so that it can send messages in a group chat without anyone interacting with it first (like sending a "Hello I'm up!" message at startup), because currently it can only respond if someone has mentioned the bot after it has initialized.
Perhaps there is a proper way to get the group chat(s) where the bot resides at the bot initialization?
I've answered before some tips on Proactive messaging, please see here for that.
To answer your question though, the bot can definitely start the engagement, either by replying to an existing message in a group chat or starting a completely new thread in the chat. However, it does require to have been installed initially, either by a user or programmatically (e.g. Graph API). That part only needs to be done once, then you can capture the conversation reference and use it again anytime thereafter. That is shown in the sample I link to in my other answer I referenced above.
It's not possible to send proactive message without prior interaction.
Sending a proactive message is different from sending a regular message. There's no active turnContext to use for a reply. You must create the conversation before sending the message.
Ref Doc: https://learn.microsoft.com/en-us/microsoftteams/platform/bots/how-to/conversations/send-proactive-messages?tabs=dotnet
I am not new to netty, even with muticast, but this is the first time I need to receive and send at the same time for a multicast program.
I need to code something that could be compared to mDNS. So every instance of my program need to reply to queries, and as such need to be able to receive query and send a reply (in multicast udp).
But the problem is that I can't send a packet without using connect() on the channel that the bootstrap class gives me, and when I do so, it seems I can't receive anymore.
So is it normal to have to create 2 bootstrap, with the only difference is that for the send one I have to connect the channel, and the receive one I must not to it.
It works, but I would like to know if it the right way to do it.
Thanks.
Note: using Netty v4.1.34.Final on JVM 1.8u181
You should be able to send by using DatagramPacket(...) and specific the remote address in the constructor.
I need to send email notification to web site subscribers. All subscribers receive simply the same thing. I can create a for loop and send one email per user, which is not very efficient as the same thing is being copied from the app to email server every time. On the other hand, I can set multiple receivers in in the "to" field. This is not good as I don't want to expose the emails to all receivers. So, is there an option to send a single email to all users and hide the receivers from each other?
Sending each email individually may be inefficient, but it is not like you have to carry each email by hand to the mail server, so it should not be a problem. If you already have it working, I would suggest that you leave it as it is. Especially since this method has an advantage which I will show further down.
If you really feel like spending time to optimize things, you can place recipients of the message in the Bcc: field. This means that they will not see each others' address. (The mail server will make sure they don't.)
There are two problems with Bcc:
Most mail servers impose a limit on how many people you may Bcc:, and it is not like they advertise what this limit is, so you might end up having to discover it yourself with trial and error, possibly accidentally spamming some people in the process.
Most mail servers will still require you to put some recipient in the To: field, regardless of who you put in Bcc:, and then the problem is that people are going to be receiving emails addressed to some unknown-to-them address, like the "undisclosed-recipients" receiver of mailing lists of old. And anti-spam filters tend to dislike this kind of recipient.
Sending each email individually allows you to address each email to its proper intended recipient. Email nowadays is plagued by spam and spam filters, so it is best to not take chances with it.
I'm hoping not to re-invent the wheel -- I'm fairly new to Java, but I need a simple but robust algorithm/code/software to perform email verification for users of a web application (e.g. I only need help with step 4 below). That is, I need to verify the user logging in has access to the email address he/she provides during log in.
The steps I have in mind for the Java middle-tier would be:
Java POJO receives user's email and password from client.
The POJO talks to a database server to verify the email/password combo is valid.
If valid, the POJO sends an email to the email address, asking user to reply to email (or click on some provided link, etc.)
The POJO receives notification (how?) that the user has replied to email (or clicked on link, etc.).
The POJO informs the web-application of success (or failure) of authentication, thereby permitting or denying access to the application.
I can write everything except step 4. Essentially I need a way to send an email to a user and then receive some type of response indicating the user received the email.
Anyone know how this can be accomplished? If not, what do you recommend as the next best/simplest solution?
I'm not using a framework as my Java middle tier is very simple. I'd like to keep the solution lean (meaning, don't want to install/implement more than I need; Spring seems overkill). I read up Shiro, but didn't find any evidence it supports email authentication. Any advice is much appreciated to help me avoid writing unnecessary/unproven routines.
The easiest way is to have some code that connects to the mailbox of the destination address, using either POP3 or IMAP, and waits for new, incoming messages.
When you send the email, you can add a Message-ID header. When the user replies to the email, there will be a References that should have the Message-ID that the user is replying too.
When you can use this ID to correlate what they are responding to.
For safety, you may wish to embed the ID within the message itself (since most folks today don't edit replies), so you can look through the body of the message if for some reason the Reference header isn't supplied. There are other techniques that let you give each mail a customer Reply-To address, that's another way this can be done, but that requires some mail server support.
But, anyway, once you have the message structure figured out, you simply listen to the inbox of the address, and look for new messages. As they arrive, your strip the Message IDs, and flag them as appropriate in the DB, or whatever.
As for "waiting" for the message, you must appreciate that it can be a long wait. Rather than having a POJO waiting for it, rather have a simple process that pings the status. You can have a timer that fires every second, and then checks the database to see if it's been updated, etc. Obviously, this is something you want to be able to cancel.
For all of the mail needs, you can use JavaMail -- it does all this, and it pretty straightforward to use.
there are two controllers involved (two POJOs).
the first connection, for steps 1,2+3 talks to one object in the server. as part of (2) a unique code (the UUID mentioned in comments)is generated and saved to the database.
the second connection, when the user clicks on the link, goes to another controller (another POJO, which could be the same class, or could be a different class, depending on your implementation). that reads the UUID from the link, goes to the database, finds the email associated with the UUID, and marks the email as verified.
update i'm struggling to see what you are missing, but when the user clicks on a link in an email the operating system opens a web browser. the web browser makes a connection to the server. the server receives the HTTP GET request with the UUID in the URL and passes the UUID to the POJO.
some more terms: the process of handling the incoming request in the webserver is typically called "routing" and the general pattern used to structure the code that is called is "MVC". exact details will depend on the application framework you are using. for servlet-based java code there's a mapping from URLs to servlets (servlets are java code implementing a certain interface - a framework might provide the servlet which ultimately invokes what you are calling a POJO, or you might write the servlet yourself, in which case that would be your POJO, although in that case it's a misnomer since it implements a specific interface) in the web.xml file.
also, i guess, the web browser on the client uses TCP to make a connection across the network (almost always this is on top of a protocol called IP because you are using the internet). on top of this, the client "speaks" messages in HTTP. all these different layers are described in the "7 layer osi network model".
there's a huge amount of detail on so many levels. hope that gets you started.
see also http://www.quora.com/What-happens-when-you-type-a-URL-into-your-browser
Hey guys,
I'm using GWT to code a simple multiplayer board game.
And while I was coding the question came up to my mind:
At first I though my client could simply communicate with the server via RemoteServices calls, so if a client wanted to connect to a game he could do as follows:
joinGame (String playerName, String gameName)
And the server implementation would do the necessary processing with the argument's data.
In other words, I would have lots of RemoteService methods, one for each type of message in the worst case.
I thought of another way, which would be creating a Message class and sub-classing it as needed.
This way, a single remoteService method would be enough:
sendMessage (Message m)
The messages building and interpreting processing too would be done by specialized classes.
Specially the building class could even be put in the gwt-app shared package.
That said,
I can't see the benefits of one or another. Thus I'm not sure if I should do one way or another or even another completely different way.
One vs other, who do you think it is better (has more benefits in the given situation)?
EDIT: A thing I forgot to mention is that one of the factors that made me think of the second (sendMessage) option was that in my application there is a CometServlet that queries game instances to see if there is not sent messages to the client in its own message queue (each client has a message queue).
I prefer the command pattern in this case (something like your sendMessage() concept).
If you have one remote service method that accepts a Command, caching becomes very simple. Batching is also easier to implement in this case. You can also add undo functionality, if that's something you think you may need.
The gwt-dispatch project is a great framework that brings this pattern to GWT.
Messaging takes more programmer time and creates a more obfuscated interface. Using remote service methods is cleaner and faster. If you think there are too many then you can split your service into multiple services. You could have a service for high scores, a service for player records, and a service for the actual game.
The only advantage I can see with messaging is that it could be slightly more portable if you were to move away from a Java RPC environment but that would be a fairly drastic shift.