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difference between network mode and non-network mode

I am having difficulties understanding the difference between network mode and non-network mode terms as used when dealing with client server applications in java.
I know how to develop simple client server apps. For example I can create a client application and server application. These applications can connect to through sockets and send and receive data. I however get confused when people talk about running a server and client in standalone mode, where both the client and server use the same instance of a JVM without loop back networking involved. I have seen this happening with the java derby database.
So my main question is how do you take code that was using sockets to communicate and convert it to use the so called "standalone mode" where the client and server run as one application? I will appreciate any comments that point me to the right material.

In the so-called network mode you have to connect to a remote server, as you describe, typically through a socket and so your client asks the server to do certain task, the server carries out the task and responds to the client.
In this mode, it is customary that the client and the server will be different nodes, that is different machines, running independently.
But what if you wanted to run you client and your server in the same machine? Even in the same virtual machine? Would it make sense to go through a socket to ask your server to do something?
That would be like using Skype to chat with a friend sat right by your side, to simply ask him to go have lunch.
So, ideally, in these cases, you should be able to run your application in non-network mode. That is, instead of going through a socket, you access your sever object directly and ask it to do something for you. Since your server object is located in the same virtual machine as your client.
Evidently, for you to be able to do this, you need a good design that exposes your server functionality through an interface, and your application uses this interface to interact with the server. When you are running in network mode, you use an implementation of this server interface that uses a socket (or RMI or whatever you do for network communication). When you are in non-network mode, you get an implementation of the server object itself.

Can I invoke a client´s method from a server with RMI

I would like to know if with RMI a server can remotely invoke a method from any of his clients, or just the clients can do this with their server.

Regardless of any implications of such a design decision, it is possible to use RMI between two JVMs that are accessible through the network. This means that if the server can access its clients through the network, and the clients have a JVM available and can act as RMI servers, then it is possible to make a client or each of the clients an RMI server and have the "server" communicate with each one of them.
Assuming the server is an application server i advise you to use the Java Messaging Service (JMS) to allow the server communicate with the client systems.

Yes, firewalls permitting. The client has to export its callbacks as remote objects and supply them to the server, typically via some registerCallback() API. Then the server just calls the methods.
However firewalls to the Internet typically don't permit callbacks, and if they do there may be issues with port numbers: you will probably need the clients to export their remote objects on a specific port which is opened in the firewall, typically 1099.

Besides the solution provided by melc, it is also possible to achieve a full duplex communication between the client and server by using WebSockets. They are now part of the Java EE 7 specification, you can read something more about them here: http://docs.oracle.com/javaee/7/tutorial/doc/websocket.htm. There are also other solutions, like Comet, or JMS (which is used like webosckets in RichFaces).

Java RMI for implementing server side of system

I am developing system, that consists of client (written in JavaFX) and server. Now I am going to implement server. Users will download clients. Clients will communicate with server (only one server and many clients). Server will communicate with data base and send results. Server will support authentication and different requests (not http of course). Is it a good idea to implement server with Java RMI? If no, could you advice me any good idea about server realisation.
Thanks a lot for future questions!

RMI is bit kind of traditional but still powerful to me ,it has some draw back . But, despite the RMI there is also a chance for you to use java sockets class ? just like a client -server application ...

Client Server Apps+java

I have a java requirment contains both client and server side program.
Server side
Server program frequently check the data base and checks if a new order came, if order came it check the order and send it to the corresponding client machine using IP address and port.The client machines are out side the LAV and has static IP address.
Client side
Client program listen a its on port , when an order came, read it and process.
For implementing these app, which java package is best,java socket communication or any other.Anybody know please suggest one.
Help is highly appreciated,
Thanks,
vks.

Don't go for low level programming like Sockets etc. Use RMI. Your program will have following two entities
Server side :
An RMI Client for calling client machine to send update after checking the database
Client side :
An RMI server application listening for Server update requests and do processing.
If you are new to RMI check out this tutorial . You can search for better tutorials if don't find these good enough :).

I remember I had to do something similar in the university and I used JMS (Java Messaging Service), documented here:
http://www.oracle.com/technetwork/java/jms/index.html
The Server will create the messages from the DB by checking it periodically and will send messages to the clients which will process the info.

Proxy Server in java

I am new to java.I need to develop a proxy server for IBC 2011 conference.I have some Questions regrading the Proxy server.
1.I am going to develop the proxy server using java.
Suppose A(sending the information) to B(receive the message) through the proxy server.
Here A is sending the information through HTTP serves(application running in A is a wed application) how can i receive the information send by A in proxy server and how can I forward it to the B which is also a HTTP serves.
2.What r the Things I have to now before I start developing the proxy server.
3.How can i get the information from the HTTP protocol.
4.How can i check frequently for the any message is there in line to forward to B from A or B to A.
Can any one helpme.Thanks in advance.

Use one of these instead http://proxies.xhaus.com/java/. Rolling your own proxy implementation will be much harder than you think once you've taken all the intricacies of HTTP into account.

there are many libraries which can you use.
for the A and B they can running hessian server(for listening) + client(for sending)
and for the proxy server you can use JMS + hessian server + client same as for A and B.
In this way you can send java objects.
But hessian is only on suggestion you can use RMI or spring remoting or maybe web services.
By far which a have working hessian is the fastest and very easy to develop.
from 1 to 4 you ask how to design a application which is out of the scope and you need to do it by you self :).

I did something similar in my course project.
As far as i am concerned, the core knowledge u need to learn about java for this a proxy server is socket programming.
you can setup two sockets: one communicates between your proxy server and the web browser, the other communicates between your proxy server and the target server.
Also, you will need some knowledge about thread in Java, open one thread for each connection will be a efficient way.
And I assume that you already have the knowledge about those computer networking stuffs like http, tcp.etc.