This might be just too crazy to accomplish but this is what I'm trying to do:
I want an very basic java program that upon running will download another java program from a certain server and run that. I'm terrible with these kind of dynamic things but is there a way to download it and run it from inside the original program?
This is something I wanted to implement to prevent the need for issuing updates, assuming the computer must be connected to the internet in order to run the app, otherwise they can't.
Java does support this, and you can write this sort of thing yourself, but JNLP (aka Java WebStart), already does this, and it might require far less work on your part than rolling your own solution.
Related
I had a question that may sound dumb to many, but I can't stop to post it here as found nothing there on the Internet.
Why does java doesn't have clrscr sort of function that we use in C?
If I created a java concole application that iterates over and over based on user input and then if I want to provide the user an option to clear the screen, then why its not supported in java.
I know there are some ways like this and this.
Is it something related to Java being OOP (I highly doubt but don't have a concrete answer).
OOP has nothing to do with it. It's more clrscr is more a function of the environment the Java is running in than Java itself, and so it is not in Java's scope.
Or to put it another way: since Java is cross platform and can be run without a console, the meaning of clrscr has to change depending on how the app is run and on what platform.
I believe it does not exist because of portability issues. Even in C, clrscr() is not really portable - not all platforms support it.
But Java was designed to be write/compile once, run anywhere. And this function does not quite fit into this agenda.
I would like to know if there is any way to communicate with a running console program (preferably running on Linux / Debian) via PHP. I am currently trying to create a webinterface for a little (existing) console Java program and I have no idea if there is any way I could do this. Could I "inject" a piece of code, lets say, a remote control module, and then use this to "remote-control" the script via PHP?
(It would be great if the existing .jar file wouldn't be changed / just injection, no reprogramming)
I am grateful for every piece of advice!
If the running program has no communication interface, then you can't communicate with it. If it does however, then the answer very much depends on how the program receives external input.
If the program contains a network listening thread (daemon), then you can communicate with it on the loopback interface using CURL or raw sockets from PHP.
Other ways of communicating with the program would be to share access to a file (PHP writes the file, Java reads it) or via a database.
The database would be the best option - it is thread safe and both PHP and Java have excellent MySQL support (Java via JDBC).
If, however you do not need to actually interface with the running program only merely need to start/stop/restart it, you can do this with the system() function in PHP.
If the Java program just runs and outputs to console, then you can do it easily enough, something like this:
$output = system( "java com.yourcompany.package.RunnableClass" );
print $output;
Assuming that the user who is running PHP has access to the Java binary of course, and that you have permission to access the JAR file.
Accessing a running program is a bit more difficult. Most programs will not have this built in by default (nor should they - giving access to random external processes in many cases is not desirable). If it does, though, you are in good shape. If it doesn't, and you can change the Java code, then you're good. If not, then you may be out of luck.
If that is the case, another good approach might be to see what resources the Java code is accessing, and how it is accessing them. Then you can write something similar in PHP. Obviously this is not ideal as you'll be re-inventing the wheel, but if you need to get to the data or whatever it is, and can't use any of the approaches above, it will work.
I'm really confused - but really it's pretty wierd because I know two programming langauges but I can't figure out something simple like this...
I've been looking for ages but I can't seem to get my head around it.
You See, for a long time I've been writting in AutoIt, and I've written two programs in it that are due to go on sale soon! They were never meant to be out for a long time though (kind of like Windows Vista), so lately I've been learning Java with success. I've wrote a few very very simple applications in eclipse while going through Java tutorials! I'm now ready to transfer my programs to Java, to gain me a wider market due to Java's cross-platform ability, but I never anticipated distribution to be this complex.
My first problem I have come across is ease of use on multiple OS's: I don't want my customers to have to deal with JRE or multiple files, I need a double click solution that will work on MAC, Windows, Linux, etc so that even complete computer newbie's can launch my software! Secondly, this is not as much a problem as something I am not sure how to do. This is including files in my software package some need to stay seperate from the program but others could be compiled, but actually I suppose this can be worked around by an installer - which would probably be easier! And finally the other proram I made is stand - alone so it can work on USB sticks (which what it was designed for), now, how do you suppose I do this so it will launch on multiple opearating systems when it's plugged in without any hasle?
Update :: Forgot to add :: My concerns about security
I have read and from personal experience I know: how easy it is to decompile a .jar, and if there not protected properly read the source code! I know about obfuscation and I know I'll have legal back up but it just worries me. Even from the point of view that user may get the wrong first impretion of my software.
So to conclude in one sentace (Please read above still):
I need to be able to let people use my software written in Java by double clicking e.g. Like something made in AutoIt - a standard application i.e *.exe
Thanks in advance
There are two routes you can take without needing any extra software involved.
The first is to just make an executable jar (Java Archive) file. Java automatically associates the .jar extension with the Java interpreter on most systems. The JAR's manifest file will tell it which class to launch when you double-click it.
The second, less recommended route, is to make a Java Web Start application, with a JNLP launcher file. The is aimed more at applications distributed from web sites.
I'll suggest the third way: write several platform-specific launch scripts for your application. For example, run.bat for Windows and run.sh for Linux. Inside every script write a command to run JRE with all the necessary parameters. You can also maintain some pre-launch checks (is JRE installed?) or some platform-specific actions in this scripts.
Suppose you're short on time and you're looking for a program with certain features, and you find one, except it lacks one feature - it cannot save and load its state. Is it possible to achieve this on OS level, or with another program, that can take the whole thing, write it to a file, and then at a later time, load it back into memory? How?
Specifically for me, this is about a Java program, but any more information on this topic is welcome.
One (heavy and easy) solution could be to use VirtualPC and install the program on a virtual OS.
Check these library's:-
Brakes
ACTC(Asynchronous Transfer of Control Threading) [Article]
Apache JavaFlow
You want to do something like the Hibernate function of Windows right?
This will be extremely difficult to implement in Java as you will also have to write the state of the JavaVM. If you had open files when you closed the program end so on.
I think the best you can do is writing the objects you need to recover to disk using Java serialization.
Have a look at the CRIU project at https://criu.org/Main_Page
It offers exactly this possibility within linux systems. Docker integrates it and offers a docker checkpoint command, which if you run your program in a container, will allow you to do this on any OS.
Thinking outside of the box here...
What possible basic approaches could be taken in an effort to create a Flex component that could run Java?
I know I can easily use flex to browse to or launch a Java app, but there are things I can only do if I can run the Java from WITHIN an MXML Component.
I the strictest sense, I know it's not impossible (ie: if you had all the source code for flex and for the jvm), but what's the least impractical means to this end?
Edit:
Lots of people are interested in the reason WHY someone might want to do this. I see it as irrelevant to HOW to do it, but here goes: I have over 100 proprietary pixel-reading windows programs that I could port to Mac in this way, much easier than any other way. But instead of arguing the premises, the winning answer will ignore the reasons why, and focus on the HOW.
Showcase your creativity.
This sounds crazy insane to me. My answer is to not go down this route. It may be a fun technical challenge for fun; but has little practical value that I can see.
Answer the question, Why would you want to run a JVM inside a Flex app?
Also, How would you use a Flex App to browse or launch a Java App? As best I understood, the security sandbox of the browser prevents you from launching other local applications.
I don't believe you are correct about not being able to accomplish certain things you "can only do if I can run the Java from WITHIN an MXML Component". With proper communication set up, you can have the Applet and the SWF simply communicating with each other through an external set of processes.
The easiest way to accomplish this is to "fake it". Load a Java Applet (This should be possible by use of the SWF's ExternalInterface API -- generate the Object tag and add it to the HTML around the swf. To make this even more convincing, use CSS to have to Applet appear "on top" of the swf. ) and have it communicate with the original swf through JavaScript calls. If that is not possible, then it may be possible to have the Java Applet generate some form of pseudo-server which the swf could then communicate with.
If neither of those work, then there is always the SWF bytearray syntax. It would need to load a ByteArray, manipulate the internal data, and then send it... somehow.
A while back I prototyped something like this. I exposed a window / native app via a VNC server and then used an open source VNC client library to connect to the VNC server. It was totally hacky but it worked. Performance was not great but was usable. Here is the Flash VNC client library I used:
http://www.wizhelp.com/flashlight-vnc/index.html
I'm with Flextras, you need to explain why before a reasonable solution can be proposed.
Unreasonable solution:
Implement the jvm in AS3. Read jars in as bytearrays. Pass the bytearrays to you new jvm.
Reasons for unreasonableness:
Implementing even a partial jvm would be at least thousands of man hours of work.
Running a virtual machine inside of Flash's already (relatively) slow vm would be like riding a golf cart that's being towed by a tortoise: either one by itself would be faster.
You can interface between Air & a Java app using merapi (although that's just communication, not actually running the api inside air)