Develop Reference

How can I connect an android with a local server?

sorry if my english isn't perfect.
I'm trying to make an app and I need to exchange information between more devices.
I thought that could be a solution connect the devices on a server but I really don't have the idea where start.
What language I need to study to make this? There is a better solution?

This highly depends on what you are trying to achieve in the first place. It would be helpful if you could tell what you are trying to do, but I will still outline some general aspects:
You need to decide, what information is going to be exchanged and how this should happen
What information: Figure out, what exactly needs to be sent and received. Generic text messages? Images? Byte Streams?
How should this be done: Generally spoken, there are two approaches of getting information as a client: Polling and subscribing.
Polling: This approach means to periodically check an endpoint for new data. For example, HTTP uses this way: A web browser or any other client (REST-Client for example) periodically requests information from a HTTP-Server, using a connection just for this single request.
Subscribing / Sync / Notification: In some way or another, the client tells the server that it is interested in the information and wants to get notified when there is something new. The connection is initiated at the beginning and held open for further usage. The benefit of this approach is that changes are received immediately, but on the other hand a permanent connection needs to be maintained.
Things to study
At the beginning, get a good understanding of the TCP/IP Protocol, how Sockets work, how common Protocols do their job (e.g. HTTP, WebSockets)
Take a look at specific Protocols working on top of the basic ones
Tip: REST: Most common WebServices Protocol, providing a common way to exchange stateless data. Uses Polling.
WebSockets: Socket connection using Web Browsers. Commonly used to update information without needing to poll.
There is no specific language to learn for connections. It's more about understanding what the difficulties are and what ways have been invented to address this. Once you get to this point and know what you want to do, it's possible in every language.
Recommendation: As you seem to use Java/Android, I would try to use REST. A really great client-side library for REST on Android is Retrofit. For the server side use what fits for you .. common Java way would be to use Jersey, but you are free to choose from a lot of choices. If using Jersey is too hard for the beginning, maybe take a look at the JS/NodeJS world, those guys invented Express, which allows you to create a REST service out of just a database, wihtout having to code a lot.

First you need to decide if you want to go for an Android or an iOS application. There are other various mobile operating systems as well, but these are widely used . If you want to go for android which is most widely used in my opinion, then you need to learn Java. If you want to go for iOS application, then you need to learn swift or objectiveC. These languages provide the API to connect with various types of services such as Facebook, Firebase and Amazon etc. If you want to connect to some other local server who’s IP is known to you, then you can use socket programming to send messages.

There could be many ways you can implement this. One way will be using Web services. Of course REST might be a better option, if you follow this approach. You can implement Your service(server side code) with any language. I will recommend you use java since you are already using android.
Aside from this You might need to go through the basics of REST, its specifications and
some reference implementations for language of your preference.

Make a GUI program to communicate with microcontroller via serial link

I want to connect my PIC micro controller to computer via serial link and control it. The MCU will send a series of bits, my program should extract useful information, so basically i should be able to work on individual bytes of received data and send some commands back. So where should i begin to write such a program ?. I have worked on C programs and simple java programs and i know bit of PHP.
It will be much better if i can make it more like a webpage so that i can host a page on my computer which can be accessed by all devices in the network and control the mcu.
Please suggest me some ideas to implement the same

If I were you, I would consider dealing with PIC or other microcontroller, because they are very low level hardware. There are some options like Arduino, RasberyPI, etc. They already have LAN or WiFi modules and cheap as well.
I would do it in a Service oriented way, so communicate via TCP/IP or UDP socket. In this way, you will have a standard interface. No mather what harware/software you have.

One way of going about it:
write software to interface your micro-controller with your computer
the pc side of the interface is most likely written in c, so learn how to interface java and c with something like jni or jna
look into java ee to create a web server
It will be very broad and require a fair amount of work/learning.

Inter-process-communication between a Java application and a local server

Firstly Cheers to all PROGRAMMERS [ Today = Programmers day :) ]
Secondly,
I'm working on a project where the specifications require using a server as a front end and an application in the back end. The project is an advanced smart home system. The server will handle commands coming from the client through the internet (let's say like a remote control from outside the house) and send them (through a channel of communication) to the application (planning on using JAVA application) which will handle the main logic like controlling hardware stuff (lights ...) , reading from a microphone (local mic) and accessing a database to act as a speech recognition system (offline).
Now I'm still in the planning phase and I'm not sure which technologies are the best for this project. I'm thinking to use Node.js or Apache as the server and a JAVA application as the back end and any SQL database for the application's SRS.
I hope this illustration demonstrates clearly how the system works:
The main question is:
What is the best way to make the Java application communicate with the server (communication channel [must be bidirectional]) ?
and Do you recommend a specific server other than the mentioned ones for this job ?
What crossed my mind so far:
1- JSP and servlets (making the server is the application too). But I don't want a server to handle the offline stuff and I'm not sure if java servlets can access hardware interface. I also want the server to be separate from making critical decisions (different layer for security reasons and since it won't be used as frequently as the local [offline] system).
2- Communication channel :
A- A shared file, but it's a bad idea since I don't want the application to check if the file contents changed (command received) or not from time to time (excessive operations).
B- A an inter-process-communication through a port (socket communication) seems the best solution but I don't know how that would turn in terms of operation cost and communication errors.
OS used : Linux Raspbian
EDIT:
I'm sure ZMQ+Apache is good enough for this task, but how is it in comparison to WebServices (like SOAP) ? Would WebServices be a better solution in terms of standard implementation and security ?
All related suggestions are welcomed, TQ

ZeroMQ is great for internal communications, or any other similar communication solutions.
For specifically your case, I can see that ZeroMQ would be a best fit.
Reasons:
You offline server have to be agnostic to web solution.
Communication can be reliable and bi-directional, possibly another patterns like (pub>sub, req<>res, etc).
Restarting any of sides would not require to restart the sockets (connection) on other side, as messages are queued.
Possibility to scale not just on same hardware, but as well to local area network or even through internet.
Big community of support. It might look a bit hard to get into, but in reality it is dead simple, just go to examples and once concept understood - it is very easy and neat to work with.
ZeroMQ has lots drivers for most popular languages, that includes Java and Node.js.
Considerations:
You need to think over packets and data will be sent. So some popular data protocols like XML or JSON is good way of thinking.
Responsibilities over different services - make sure they are not dependant on each other too much. Or if main offline server - is a core of system, make sure it does not depend on web facing service, so that web face can be removed/replaced/improved etc.
Few more points to think about:
Why Java, and what about modular approach? For example if you want to expand and scale - add more sensors into smart home solutions, then having one giant application would require to change it, it is harder to maintain as well as maintain different clients with own needs. Think modular way - some core functionality for offline stuff, but many aggregator processes that would talk to different sensors. This makes easier to support different setups and environments, as well maintain the system as a whole by improving independent components.

How can I implement a good Client-Server approach?

I'm developing a distributed application, and I need to connect a client Java based to a server C++ based. Both of them will need to send information to each other, but I need them to be able to do things while waiting for the information, and they don't know when they are gonna get new information, or send information.
How can I achieve this? Now I'm trying to implement a basic communication with Sockets, but I don't really get to communicate them. I have read that using sockets + threads is usually a good approach for client-server apps.
Could you please recommend me some web or book to read about this, or send me some example code to learn?
Do you think that i should use other approach, better than sockets? maybe a higher level library (i would need it for c++ and java) or a totally different way?
EDIT:
I will add some extra information.
What I would love to achieve is the following:
My C++ program has a main loop, where I would like to have a call like GetUpdatedDataFromRemoteDevice() where I read the new values of some numerical variables that previously got updated from the net (the socket, for example).
Eventually, the C++ program will need to send a message to the remote device, to tell him to send other kind of data, and after that, keep getting the updated values.
From the Java program (remote device) the application running is an interactive touchable screen, that cant get blocked by the network transmissions, because it must keep working for the user, so all the networking should be done in a separated thread.
That thread, should connect to the server, and when a button is pushed, start to send the data (4 changing numerical values) in a loop until another event happens.
It would be nice also to be easily re-connectable to the server.

ICE is a modern and good library for distributed applications:
many languages as C++ and Java
many platforms
GNU GPL
good performance
easy to use
First, you define the messages you want to exchange between server and client.
Then, you implement the C++ and Java source code to handle these messages.
More info at http://zeroc.com/ice.html
Have fun ;-)
EDIT: I have to use ACE in some projects. I can tell ACE is very old, maybe mature, but uses outdated C++ coding rules :-(
Therefore ACE is not as easy to use as STL or BOOST. Moreover, ACE is not really efficient... I prefer ICE ;-)

I don't know what your application is but robust client server socket programming is pretty hairy task to do properly. Hardware byte order, String encoding, Network errors, retries, duplicate messages, acks etc.. require lots of good design and careful programming. You need to get it work well as single-threaded before even thinking using multiple threads.
Unless you need instant notifications from server to client I suggest that you use HTTP as protocol between client and server. Client can poll server occasionally for new messages.
Anyway the problem has been solved multiple times already.
http://activemq.apache.org/
http://www.rabbitmq.com/devtools.html
http://www.cs.wustl.edu/~schmidt/ACE-overview.html

I did something of this sort once. In my case it was easier to connect my C++ app to a local Java app using JNI and then have the two Java apps talk to each other.

Grid Computing and Java

I couldn't seem to find a similar question to this.
I am currently looking at the best solution solving a grid computing problem.
The setup:
I have a server/client situation where there clients [typically dumb of most logic] and recieve instructions from the server
Have an authorization request
Clients report back information on speed of completing the task (the task's difficult is judged by the task type)
Clients recieve the best fit task for their previous performance (the best clients receive the worst problems)
Eventually the requirements would be:
The client's footprint must be small and standalone - I can't have a client that requires lots to install and setup
The client should be able to grab new jobs and job runtimes from the server (it would be nice to have the grid scale to new problems [and the new problems would be distributed by the server] that are introduced)
I need to have an authentication layer (doesn't have to be complex or conform to an existing ldap) [easier requirement: clients can signup for a new "membership" and get access] (I'm not sure that RMI's strengths lie here)
The clients would be able to run from the Internet rather in a networked environement
Which means encryption of the results requested
I'm currently using webservices to communicate between the clients and and the server. All of the information and results goes back to the hosting server (J2EE).
My question is there a grid system setup that matches all/most of these requirements, and is open source?
I'm not interested in doing a cloud because most of these tasks are small, but very frequent (once a day but the task may be easy, but performs maintenance).
All of the code for this system is in Java.

You may want to investigate space-based architectures, and in particular Jini and Javaspaces. What's Jini ? It is essentially RMI with a configurable discovery mechanism. You request an implementor of a Java interface, and the Jini subsystem finds current services implementing that interface and dynamically informs your service of these.
Briefly, you'd write the work items into a space. The grid nodes would be set up to read data transactionally from the space. Each grid node would take a work item, process it and write a result back into that space (or another space). The distributing node can monitor for results being written back (and.or for your projected result timings, as you've requested).
It's all Java, and will scale linearly. Because it's Jini, the grid nodes can dynamically load their classes from an HTTP server and so you can propagate code updates trivially.

Take a look on Grid Beans

BOINC sounds like it would work for your problem, though you have to wrap java for your clients. That, and it may be overkill for you.