I had a query related to java programming. I have two wifi modules connected to my access point and my android phone connected to the same access point. Can I send a string message to any of the two modules from my phone using only MAC address? I dont want to create a server on my phone.
Any help is much appreciate
"Can I send a string message to any of the two modules from my phone
using only MAC address?"
Theoretically: Yes, but hard work.
You would need to implement a transport-layer protocol just for that. What speaks against using the IP stack? It has some more overhead in comparison to just sending the messages based on Ethernet but that overhead is totally okay in comparison to the effort you had to invest in building the your own protocol-stack.
"I dont want to create a server on my phone."
You don't need to create a server on your phone. The other two modules do need a "server" that is listening for the message from your phone. Your phone would need to run a client capable sending the message to the other two modules.
Please don't misunderstand me here, but from the question you are asking I'd say working on such a project with that little knowledge would be very frustrating.
If you want to pull it off I recommend having a look at Jpcap. It is a Java library that is design to capture and send network packets.
You can't do any I/O in Java based on a MAC address unless you are prepared to use third party stuff.
Related
I would like to manage a connection between 2 applications, they will run on diffrent phones.
The purpose doesn't really matters let's say that it would be some kind of a chat.
How can I create this connection between the applications? I know how to do it on pc java programs using the socket and the serverSocket classes but I guess it's diffrent in here since the phone might change his ip when he moves between networks.
So how would you do that? how would you create a connection between 2 applications/phones
Given the scenario you described in your comment, using Push Notification i.e Google Cloud Messaging (GCM) might be sufficient.
So, when program B wants update from program A, it will ask the server to push a notification (via GCM) to program A. Note that program A will not connect to the server every x time to check for updates.
Another out-of-the-box solution is to use SMS if the communication is not so frequent and messages are short. Here I mean SMS that will be processed directly by your app (given it has certain attention word) and will not go to the inbox i.e. no SMS notification on the phone
Since the two phones will, as you note, have changing IP addresses, you'll probably need to use an intermediary.
The general design pattern here would be to have a server with a fixed IP or DNS address that relays messages between your two mobile devices. The simplest implementation would be a webserver, to which each phone would connect via HTTP(S) to transmit data or poll for updates.
There are a number of backend-as-a-service platforms that provide this type of functionality pre-built, and would likely suffice for something like a chat system. Check out Cloudmine and Parse.
If you need a low-latency or near-realtime connection, you could also consider implementing your own server that uses the Android C2DM (Cloud to Device Messaging) service.
See Android's Sample Bluetooth Chat App, It will give you an idea for how it can be achieved.
my apologies if this is a trivial question.
I've recently begun doing some android programming and I'm writing a simple app that allows you to use your android device as a controller for your windows PC. Specifically it allows the user to do things like turn off the machine, make it sleep, reboot it etc etc. I'm currently using a python library called CherryPy as a server on the windows machine to execute the actual win32api calls to perform the desired function. What i'm not sure about is how to discover (dynamically) which machine on the network is actually hosting the server. Everything is working fine if I hardcode my machines public IP into the android app, but obviously that is far less than ideal. I've considered having the user manually enter their machines public IP in the app, but if there's a way to, say, broadcast a quick message to all machines on the WiFi and check for a pre-canned response that my Python server would send out, that'd be wonderful. Is that possible?
Thanks in advance guys.
Try sending a UDP packet to the special broadcast address 255.255.255.255. Every device in the network should receive a copy of that packet (barring firewalls), and you can arrange to have the server reply to the packet with its identity.
Write your app using the alljoyn framework. AllJoyn will handle these details for you.
Initially, ip-addresses from the ISP are always changing. I am working on an android app and I need to connect from outside my home to my internal network. I need a server connected to my modem/router and the server should save the public ip of my home network every time it changes.
Goal: make a communication between my android app and the modem/router.
My question is:
Do I have to program an app on the server side to do this job, or is there an app already available?
If none are available, could you please tell me the steps to create one, or any references to that end?
Thank you!
I think your best bet is to use a dynamic dns service. That will allow you to give your machine a string name, run the app they'll give you (or many routers support this built-in), and just reference the computer by name when you need it. See http://en.wikipedia.org/wiki/Dynamic_DNS
Let's say I have two android mobile devices, connected to the same wireless network, and that network hasnt external/internet access.
Without third party software, is it possible to transfer data through wifi without knowing the ip from each other and without creating an hotspot? Something like we do on Windows (if 2 pcs are on same network, they can share information directly without internet access)
Starting with the basics, I would like to develop an application, where android phones on same network appears on a list , and then a user choose on of them and writes something - and if the other user have the same app running, appears that on his phone (and then he can reply of course - basically, a chat.
I know this make no practical sense, but believe makes all the sense for what I need to do (it's not a chat of course). If anyone knows anything, please help me - i found nothing.
Thanks in advance.
If you want to send data or messages from one phone to another using the network you will eventually need the IP address of the recipient phone. However, If you don't care about targeting specific phones you could always send UDP broadcast packets that each device on the network should receive.
If you don't want to manually specify an IP you'll need to create a discovery protocol that a phone uses to discover all the other phones on the network. You could do this buy scanning all available IP addresses and checking to see if they are a valid android phone. Or you could have each phone broadcast its presence on the network using a UDP broadcast packet sent to a predefined port.
Once you have discovered all the phones on the network its really up to you to decide how you want to send the data between phones and there are hundreds of examples of how to send data between devices/computers/processes using sockets.
I have a Java program running on two computers that are both on the same network. I would like to have these applications become aware of each other, so they could communicate directly as opposed to communicating with the server to relay messages.
I believe i may have a solution as to how this would work, but am unable to find any examples to compare my solution against. Do you guys know how this problem is usually solved?
There is a good library that implements the Zeroconf / Bonjour standard in plain java at http://jmdns.sourceforge.net/
This basically relieves you from the protocol burden and allows you to advertise and lookup service providers based in logical names (That's what iTunes or Mac printing does for example).
This book http://www.amazon.com/Zero-Configuration-Networking-Definitive-Guide/dp/0596101007 explains all basic concepts.
You could get them to do a UDP multicast within a LAN environment to identify the programs using protocol messages then have a stored cache of each other's identity and then use TCP to connect and do main exchanging of messages (which is more reliable than UDP). Or you can simply proceed with UDP messaging only if you want to.
You can search for multicasting in Java online.
Some multicast related links:
http://download.oracle.com/javase/1.4.2/docs/api/java/net/MulticastSocket.html
http://www.javafaq.nu/java-article817.html
A good multicast chat software you can reference:
http://sourceforge.net/projects/mc2/
One way would be to send a broadcast to see who's out there, then implement a GUI to show the user what other peers are there and give an option to connect to. (The broadcast will give you the IP address of everybody there.)
Once you know who to connect to, you simply open a TCP connection (or use UDP if it is time-critical) and you're done.
Btw, this is for IPv4 - IPv6 doesn't have broadcast (although something similar).