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.
Related
I want to connect my android application to an applet which is running on my pc on Google chrome on Wi-fi.. where my phone works as a wi-fi hotspot and pc as the connected device. I want the connection to work uniquely as I want commands to be passed from my application to the specific applet, on the execution of which my applet does specific tasks. Please tell me the APIs which I can look in both Java and Android or the technology I have to use to make it work..
You need to use any program, such as wamp server, to make your computer to be a localserver. It will install PHP 5, MySQL and Apache. In other hand, you will also need a little bit of knowledge in Php language to create you own web services.
Another thing you need to be aware is that to handle you connection between server and device (and by this I mean which IP you are going to use) you will have a little headache; but first things first..break your problem in little parts thus will be easier to solve them.
I recommend this tutorial.
I think the simple way to connect these two softwares is using UDP.
It is fast, it is easy to program but it is generally unreliable according to TCP. But it is already local network. I dont think that is a case you need to take care in your local wifi network.
So take a look at this tutorial http://tutorials.jenkov.com/java-networking/udp-datagram-sockets.html
There are other ways like https://www.alljoyn.org/. It has more functinality but more complicated.
You must install Server on your PC(Apache httpd or apache tomcat or other based on your interest). A server listens to request from clients. When your mobile is connected to your pc(doesn't matter wire or wireless), you can make a request to an url(say, localhost:8080/welcome) from your app.
Create an applet and connect it with your web application(in the server) using java.net.URL and java.net.URLConnection.
On performing some operation on the client, call the url of the server application and forward the response to the applet.
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.
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
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.
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.