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I have a working java app and now I would like to extend it to be controlled over ssh. Let's say I have a swing button that increases a counter. I would like to be able to ssh in that computer and say something $: myapp increase and have the button's action listener executed.
Maybe I'm using the wrong keywords but I could not find a solution. The 'kinda' solution I could think of is using signals but I'm not even sure if they can be used as I am used to from C and if that can be done without knowing the actual process ID.
Any material that can get me started would be welcome.
signals are hard to read from java, because there is a lot of difference between OSes on how to do those (some don't even have the concept), and java is designed to expose anything that can be generalized across all OSes java runs on, and to not expose anything that might not be there.
The usual way to do it, is via TCP/IP (so, java.net.Socket), or HTTP (so, jetty or some such).
Note that webapps can trivially be accessed remotely and can be scripted fairly easily. You could also consider building a command line / terminal based app, for example with lanterna which you can shove into a terminal session keeper / eternal SSH kinda deal.
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Suppose I have to run a java, c++, or python3.8 program on my machine, but I don't want these programs to access my system information, run os commands, or perform any malicious activity. Is there a way to do this for each of the aforementioned languages?
Java theoretically has a solution for this: The 'SecurityManager'. You can set one up within your java code (you can tell the system: Here is some code; load it as the manager please).
A securitymanager gets called before certain things happen and can deny the operation. It's mostly anything that feels security sensitive:
Quitting the VM
Opening any file
Opening any network connection
Setting the security manager
accessing clipboards
Printing things
Can influence certain aspects of thread loading
You'd tell java to run some class file that you wrote, that class file sets up a security manager, and will then run the application you want to restrict.
Note that you can't really restrict how much memory and/or CPU it uses with a SecurityManager, which can be quite an issue by itself.
The problem is, the primary use case for this mechanism is to run applets, and applets are long dead. Thus, it's a feature that few people in the java ecosystem are currently using, and little-used blacklist-style mechanisms are usually riddled with holes.
I'd strongly suggest you set up a virtual machine for this purpose. There are leaks in hypervisor based restrictions too, but 'host things in a VM and ensure it cant do things to the underlying machine' is a lot more common.
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I have heard sometimes that the front end of a program was written in language A and the back end in language B. Can i do it for desktop programs I make too? Like do the graphics with Java and the back end with C or C++. How do i do it?
PS. Sorry if its a newbie question because I am one.
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Because i am told that my question is too broad, here is what I exactly want. How can I link mt action listener in java with a C program? For example, if i have a button "next hundred primes" i want the button to be made in Java and primes calculated using C.
This can be done in one Java process with JNI, for example. Java effectively calls C++ as a library.
This can also be done multi-process by having Java process create a C++ process then capture its output as, for example, C++ process exit code, standard output or created file.
A third way to do this would be to have a long-running C++ process listen on a TCP socket then have the Java program communicate with its C++ back-end over the network, either on the same machine or across an intranet.
Other methods also surely exist. These are just a few I know off the top of my head. :)
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I am not a Java pro. I need to enable my completed java applications to ONLINE-Versions. Kindly give me the simplest way.
I have tried to go the JSP and Servlet way, but seems exceedingly tiresome,there surely ought to be a direct way.
When you use a typical web application what do you think is happening? You're in a browser and it's displaying some pages. You click around and some server does some work, for example Amazon shows you a list of books you could buy, the server is passing data to the browser for it to display.
That's a big difference from your current Java Application where everything is happening in the same computer.
This split between the UI part of the application, in the Browser, and the server part that's doing the real business is one reason why Web programming is so different from simple Java programming.
Servlets and JSPs are the traditional Java way of doing things, but modern web apps make much greater use of JavaScript for all the UI and all the Java (or any other server technology) does is provide the data displayed by JavaScript.
Bottom line: Sorry, but there is a whole lot more to learn. My recommendation would be to grit your teeth and forget about what you've done so far and start studying JavaScript and HTML.
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Can you program external application from Java app.?
I know this is a wierd question but lately I really need to do it.
So the lets say I have "VLC" player or MPC or whatever it is, I want to be able to create a Java/C++ application or whatever it is to control the application such as play the video, pause the video and stuff.
If it possible please let me know and how.
It's certainly possible with VLC. Look here: http://wiki.videolan.org/Java_bindings as well as here: how to control VLC by java
For MPC, I don't know of any resources that can be used to do so. You can at least launch it to the best of my knowledge.
To start (execute) an external application you should use Runtime.getRuntime().exec(params);
or ProcessBuilder class.
http://docs.oracle.com/javase/7/docs/api/java/lang/ProcessBuilder.html
See Execute external program in java for more information.
To send key strokes to another application you could use the "Robot" class (http://docs.oracle.com/javase/6/docs/api/java/awt/Robot.html).
What is expected is to have access to interface to do these operations, you can get some references from http://caprica.github.io/vlcj/
This is java api for controlling the VLC instance embedded in AWT.
I have found this site that describes how to run external programms from java
http://www.rgagnon.com/javadetails/java-0014.html
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I'm trying to make a prototype for the company that I'm interning for. I would like to create a program that allows users to make minor updates that will, within 15ish seconds or so, update on everyone's screen. This program will only be used by about 20 people at one time at the most. For instance, if a person were to type click a button that went from red to green, the change to green would show on everyone's screen. I only know Java, but I'm not opposed to learning other languages. I'm just looking for places to read about this type of stuff, or ways that you know to do it.
I'm also hoping to allow an admin account to make usernames for people with differing amounts of access to making updates, but this is the later part to my project.
Thanks
With only 20 users or so, your options are pretty much wide open. You can use TCP or UDP, a web server with HTTP. I'd use TCP myself.
It will be easy to update only 20 people with small updates within 15 seconds.
Here's how to create a TCP server in C#.net
Here's how to create a simple TCP server in Java.
I suggest using ProtoBufs for the binary protocol. Its simple, compact, and allows you to change your language without needing to rewrite protocol parsing/unparsing code.