I am setting up a home server on an old PC, but I am not using a server like apache, instead making a really basic one in java. I have got a extremely basic linux kernel compiled and working on it. But I want a gui along with my program. Is it possible for me to do it without installing X11 or wayland on my system?Note: I dont have anything on my system apart from the necessary java files.
You can run Java applications on headless mode on server environment.
From Oracle docs:
Headless mode is a system configuration in which the display device, keyboard, or mouse is lacking. Sounds unexpected, but actually you can perform different operations in this mode, even with graphic data.
It means you can run some AWT graphic stuff, even without X11, but obviously, not visible in your screen. As example, you can create graphics with java.awt.Canvas and save/export as a image. Available AWT classes in headless mode are: Canvas, Font, Image (and subclasses), Print classes and Beep.
See detailed info here: Headless Java SE
Related
I have created a program using Java 8 that utilises a Swing GUI in the Eclipse IDE. To scale images and icons to appropriate sizes, it gets and uses the screen resolution. Upon compiling the program within Eclipse, the program displays perfectly fine, and everything seems to operate as it should. However, when I export the project as a "Runnable Jar", and run the program, the image scaling and the program look and feel are all off.
Upon further investigation, it appears that the runnable jar was returning a screen resolution that is exactly 2.5x less then that in eclipse (which is the actual resolution - 3840x2160 vs 1536x864). There is circumstantial evidence across the internet that Java 8 Look and Feels (or something of the sort) don't support HiDPI screen scaling. There are scattered solutions that claim to fix the problem, like updating to Java versions past 8, or by adding arguments to the jar compilation (whatever that means). This is already confusing to a Java novice, and it is only made more confusing by the program being displayed perfectly when run/compiled within the Eclipse IDE.
My question is whether anyone knows how to get a program compiled in Java using Swing to scale correctly on an HiDPI screen, and what the process is that I need to follow to compile a working program?
EDIT 1: Something interesting to note is that in my Windows settings, the "Scale and Layout", "Change the size of text, apps, and other items" is set to exactly 250%, meaning that this setting is obviously the cause of the scaling issues I am encountering. Does someone know how to bypass this setting from within the program, or why it works when I run it through Eclipse?
Java 8 does not support High DPI. On Windows, it runs in DPI unaware mode and relies on Windows to stretch the window bitmap to the scale set for the monitor in the settings. It means the UI of the application looks blurry when displayed on a High DPI monitor.
Later versions of Java, Java 11 and above, support per-monitor High DPI settings. The UI of your application is correctly scale up according to the settings, the text remains crisp. For the icons and images to remain crisp, you should use MultiResolutionImage or its basic implementation BaseMultiResolutionImage to provide higher resolution alternatives.
You should not base your images based on the screen resolution but rather on the scale set for a monitor. For example, a Full HD monitor 1920×1080 with 150% scale has the effective resolution 1280×720, it is the effective resolution that Java reports to you.
I have a legacy Java application that uses Java 1.3
It works fine on windows Xp but now I need to make it run on windows 7.
I have installed the 1.3 jdk however when it first loads, the app won't render properly. Bits of the screen just show grey background, selecting buttons won't load a new screen etc.
I do know watching the output from the app it just purely graphics not rendering properly.
However if I press "Ctrl-alt-delete" and then just press "cancel" the software runs perfectly.
If I have a second monitor plugged in, it runs perfectly.
Has anyone got any suggestions how to make app run perfectly first time.
Thanks
Firstly, update your java, no excuses not to.
You can try the hack of resizing your component to a different size and then back again. I find this is the best way to make sure that swing doesn't do this sort of mischief with black squares here and there.
These things happen from time to time with non native tools for desktop development as opposed to those specifically designed for the targeted platform.
I have some java code that I use on a windows machine that runs as a service and has a tray icon that I want to port to Mac OS X. From what I can tell there is no good way to make a menu bar icon using java, so I want to basically wrap my java code with objective-c so I can have a nice menu bar icon and still interact with the java code as I am able to when running the code on my windows box. Is there a good way to do this?
My java code makes web requests every so often so the main functionality I'm looking for is to start/stop the web client, as well as receive updates from the java code on the status of the web requests (more or less push notifications).
Thanks for your help everyone!
If all you're trying to do is get your application's icon displayed in the Dock & the Finder, you don't need to write an objective-C wrapper; all you need to do is bundle the Java code up in with the icons in an OS X "application bundle". See Apple's Java Deployment Guide
You might also want to look into the com.apple.eawt package (see questions/1319805/java-os-x-dock-menu), which provides some features to allow a Java app to appear more like a native OS X application to the user (for example, supporting drag-and-dropping a file to the application icon).
How can I disable OS-level keyboard shortcuts (e.g. Alt-Tab, Ctrl-Alt-Left/Right, etc.) on a [Ubuntu] Linux machine? I'm developing a full-screen Java Swing app and don't want the user to be able to task switch away from the program arbitrarily. It's not enough to toggle the "always on top" flag; users mustn't be allowed to switch workspaces, migrate focus or any other such things. The machine must function normally before and after the application is executed. Google says that this will require JNI or JNA but I'm looking for a bit more hand-holding.
There's no point in trying to do this in your application because any of these changes are going to need to be handled by X11 and/or the window manager since those are what respond to the commands. Assuming that you have control of the platform, choose a window manager which supports a kiosk mode. Then use the window manager's settings to start your application and enter kiosk mode.
Options for window managers which can do this include KDE or twm-kiosk.
(And if you don't have control of the platform, you're not likely to be able to have your application intercept things like ctrl-alt-backspace anyway.)
Edit:
In response to a scaled-down version of the question in which he's willing to let things like ctl-alt-backspace go and just wants most of the keys including alt-tab or other similar application switching key combinations, the following should work:
You should be able to do this using XLib's XGrabKeyboard method through JNI. This Java/XLib JNI keypress capture tutorial should be a good starting point. However, it uses XGrabKey which just passively listens for keys and does not prevent other applications from receiving them. You'll instead want to use XGrabKeyboard which actively snags all of the normal keyboard events (which, if the premise of this StackOverflow question is correct, includes the task switching keys).
Note that as a side-effect, key capture in Swing will also probably stop working because your Swing windows are going to be separate from the window you create in C. As such, you will probably have to use your JNI interface to get key presses to your program when needed. (Although I would definitely advise testing it first before writing the code.) You might be able to avoid this if you can get the window using Java AWT Native Interface to get the window ID. (Note that Swing is built on top of AWT, so this will work for Swing.) However, I'm not sure how to do this. It looks like you might be able to navigate the window tree by getting the root window from the Display and going from there to find your Window, but it's all kind of weird. It would be nice if the AWT NI just told you the window ID, but it doesn't look like it does that.
As this warning Reminder: XGrabKeyboard is not a security interface notes, this doesn't make it impossible for other programs to see the keys, but it seems likely that window managers will not be using XQueryKeyMap so it is likely to prevent task switching.
I want to to render an application (e.g. a browser) in memory (not on screen) and stream the result of this rendering to a couple of remote desktops.
What options do I have? Is there a Java framework (maybe based on OpenGL) that I can use for this?
OpenGL is a drawing API; totally unsuited for your demands; just telling you to clear things up.
The whole "do the thing off-screen" requires to hook into the lower parts of the graphics system. With Java this means serious tinkering with the JNI and probably also some native binary code. IMHO not worth the effort, as there is a much nicer solution:
Xorg has a X server that is backed by a VNC framebuffer (Xvnc). You can start a browser in such and if there's no window manager and desktop environment running, the browser will be the only thing visible, no decorations, titlebar or the like. Then you connect using VNC to that server and will see the picture of the browser only. Technically VNC is just a video stream of JPEG images, and there are tools to create a regular video stream from VNC.
X provides you an additional possibility: The Composite extension. X Composite provides a mechanism to transfer a window into an offscreen rendering area. The contents rendered to the offscreen area must be composited to the screen by a so called compositor. It is possible, though quite inefficient, to copy those offscreen images into process memory and from there build a video stream.
Depending on what you are trying to do, you could run you application on a linux box and stream the output of the application over SSH to an xserver on another machine. I believe that there are xservers available for Windows and MacOS, but this gets you pretty far away from Java.
http://www.vanemery.com/Linux/XoverSSH/X-over-SSH2.html