I have a jar on a server, and users should be able to develop extensions for it. Therefore the jars main class should be extended and some resources should be added to a second user created jar which will be loaded from another server or locally. Now I have problems accessing the resources (images) from the user loaded jars. Heres is the structure:
My Server:
game.jar containing
game.class
images.class
...
image1.png (...)
Local:
user.jar containing:
user.class extends game
userimage.png
The extension is loaded via Greasemonkey, it modifies the "archive" attribute to "/home/username/user.jar, game.jar" and the "code" attribute to "user.class". The user should be able to overwrite already defined images. If the image does not exist in game.jar, it is loaded correctly from user.jar. But the images loaded early in the game are always loaded from the game.jar, others seem to be overwritten correctly by the user. Is there a way to make sure they are always loaded in the correct order? This might be because of some caching mechanism. Because Greasemonkey removes the game from the page, changes the archive and code and reinsert it, the game is loaded without a mod for a brief second. In that time, images are loaded as expected from game jar, but those are the ones not being overwritable by the user. But how to avoid it?
Another thing:
If I overwrite the "run" method in user.class, the game is unable to load any image at all. Not from the user.jar and not from the game.jar. Java doesn't find the image, as the URL object "getClass().getResource(imagename)" returns with null. I tried to overwrite the image.class, but that doesn't fix the problem, unless I overwrite every class from game.class involved into calling the image.class
I don't think having greasemonkey monkey with the <applet> tag is necessarily the best approach here. Perhaps you should actually have the greasemonkey script communicate with your applet and tell it what is wanted of it?
Of course, that leaves the question of how to have the applet wait for the script, but only when there is such a script...
Related
It is as simple as an application that can update itself.
More specific, maybe a launcher that loads a jar file from the web and replaces it with the current jar.
The approach that I want is:
A launcher which is coded in Java.
That launcher overall uses classloader e.t.c.
I want to keep the data from the previous jar. Maybe the data from the previous jar are written on a .txt file and pass them to the new one? (If possible)
I have no clue about classloader or any direction to follow.
So my question is "How can i use classloader to create an auto-update Java application?".
P.S. I want java web start to be the last choice. Some lines of code would help me very much.
Edit: I understand completely what are you saying in theory. What i am looking for is specific links or code which i can take as reference.
The question isn't a duplicate because i can't find links or code but theory.
You can use the URLClassLoader to load a jar file from an URL. Mind, URLs may also be local files, and I'd recommend that you download the jar file locally before loading it in, instead of loading it directly from the web. The reason for this is that you want the application to remain usable, even if the user cannot reach your server.
However, I'd also recommend against taking this approach. What if you want to update the launcher? It's better to download a seperate updater application from the main application, launch the seperate updater application, have that kill the main application and update it.
I’m coding my first java Desktop application using eclipse and I’m having difficulty deploying it. My project uses JavaFX2 and the e(fx)clipse plugin, the latter is in charge of generating the build.xml file.
ABOUT THE APP
The app, amongst other things, provides an interface where the user can create categories and associate these with labels. All modifications are saved within a single file (the data is stored as a serialized object.) and are supposed to be loaded automatically when the app is reopened.
THE PROBLEM
When build as an executable jar using a .xml file (Ant), the project runs fine within the folder where it gets created. I can run my application, modify data, and save everything once I’m done. When I reopen the app everything gets loaded as it should.
However, if I copy the folder elsewhere, I can no longer save any data. Everything else seems to work; the app will even load the data that was saved when it was in its original directory. I assume that this means that the app can still see the data file, but can no longer write to it.
WHAT IVE TRIED
I’ve read that warping the .jar around an installer may fix the issue; however, one of the goals for the app was to make it as portable as possible. Meaning that it should be possible to move it around from one directory/computer to another, ideally in a manner that is cross-platform friendly, without the need of installing it.
I’ve tried various things to get it to work. I’ve shifted the whole project to Netbeans (to produce a different build), I’ve modified the save/load method file path to make sure the right document is targeted, I’ve tweaked the .xml file the best I could, and I even tried to build the project using the javafxpackager. No matter what I do, when the build works, I get the same results.
Right now, I’m thinking that there may still be something wrong with the .xml file but I’ve got a hard time understanding how to modify it. Perhaps the problem is somehow caused by the way the data gets serialized. I know that at one point when I moved things around within my project, both the save and load methods could no longer interact with the data.
What I find strange is that when the project is moved the load method still works. If the problem is caused by changing the file path, how come only the save method ceases to function?
APP FILES AND STRUCTURE
+src
-(Main.java)
+controller
-(misc.javas)
+modelData
-(Library.java) -->the object that is serialized
+modelLogic
-(misc.javas)
+view
-(misc.javas)
+files
-(library.data) -->the file where the serialized object is saved
+lib
-(empty.empty)
So, is their anything I can do to solve my problem?
Thanks in advance.
In the end, the problem was rather simple. When I was moving the app, I was always putting it on the desktop, which, in the case of my PC, sets by default all content as read-only (in relation to the app's privileges). Because of this, the app could not modify any files that were within folders on the desktop.
Therefore, all I had to do was to move the app to another directory, such as C:\randomFolder, and the problem was solved.
So, if anyone has a similar problem, moving the app elsewhere may be the solution. Alternatively, taking full ownership of the folder and its content can also work.
When possible, it is usually better to have the app ask its user for a specific location to save its data.
I currently have a in-development Java Game.
It runs from a .jar, with all the image files inside. The .jar creates and accesses files in the working directory.
I was wondering if there was a simple way to put this on a webpage as a Java Applet. I currently have Applet code in the Game, but all it does is calls the normal main method to create JFrames and run the game.
I need a simple way to run this on clients from a webpage, prefferably an applet? Is there one?
Please note, I didn't actually make this as an Applet at first. It's currently a .jar, with a .bat to run it. My "Applet" class is this simple...
package explorer.applet;
import java.applet.Applet;
import explorer.boot.Startup;
#SuppressWarnings("serial")
public class ExplorerApplet extends Applet{
public void init()
{
Startup.wp = true;
Startup.main(null);
}
}
I was wondering if there was a simple way to put this on a webpage..
Sure. Launch a JFrame direct from a link using Java Web Start.
..as a Java Applet.
Why? Applets are harder to deploy and maintain, and provide a less satisfactory experience to the end user.
Note that the fundamental problem is the same either way. 'How to access an application resource?'
Such resource access would be by URL. There are these 2 primary alternatives:
Add the resource to the Jar and use Class.getResource("/path/to/the.resource")
Put the resource 'loose' on the home server, and form the URL relative to the code base or document base of the applet, or the code base of the JNLP (the file used to configure a JWS launch).
The .jar creates and accesses files in the working directory.
About 4MB, and they store the game information. (It's a 2D world game.)
They also have to be client side, and in the folder that the "jar" runs from.
That is too large for any of the sand-boxed techniques I had in mind, but since it is 'static'1 resources - they can be added to a Jar which is on the run-time class-path and thereby will be 'downloaded and made available to the app.'.
Access the resources as described above.
By 'static' I simply mean 'do not need to be edited or changed by the user or app.', as opposed to something like 'high scores' which must logically be written by the app. on game exit. It is still possible to update the maps, all you need to do is provide the updated Jar and Java will do the rest.
I have been using IntelliJ for a while now and I'm enjoying its suite of features but I'm having a hard time getting the run configurations to work for a java applet. I have a pre-existing Java tool that uses Swing and I'm using the JApplet class to load those GUI objects as an applet. The problem is I have a couple configuration files that I need loaded. I load these from the working directory and from my knowledge, this working directory would normally be the directory in which the applet resides. I think the major problem is IDEA sets the startup variable:
-Didea.launcher.bin.path=IDEA_BIN_DIR
I would like to be able to change this but I am seemingly unable to. I have tried overriding this flag by editing the applets run configuration VM parameters, but IDEA will continue putting the above one in even if I specify something different.
So in short, I'm having a hard time loading a local configuration file because I can't set the working directory for the run configuration in IDEA. Does anyone know how to get around this or know of a better way of running Java applets that use configuration files, in IDEA?
An applet normally runs in a sandbox in a browser, and such an applet can't access the local computer's file system, for security reasons.
Thus it is generally a bad idea to load configuration files from the file system, and "working directory" is not a useful term for an applet.
If these files change seldom (i.e. in principle only by the developer), you can put them to the applet's class files (i.e. in the jar file, or during development in the directory where the classes will be generated), and use class.getResource() or .getResourceAsStream() to load them.
If the configuration files should be definable by the webmaster, put them on the webserver - either at some fixed location relative to getCodeBase() or .getDocumentBase(), or specify them as parameters to your applet tag in the HTML tag.
If these are user specific configuration files (which the applet should be able to write), you either need to store them on the server and retrieve/store after a login (i.e. you need some logic at the server side), or you would store them at the client side.
The current way to do this would be using the JNLP API (in javax.jnlp.*) - there are some interfaces allowing Persistence, or loading/storing data (with the user having a FileChooser). Alternatively, you could sign your applet and request an AllPermission from the user - then you can access the file system.
Sorry, nothing of these answers your original question (I don't use IDEA), but maybe these help you to find another way.
I'm trying to use this tool
https://swingexplorer.dev.java.net/
to find some information out about an applet's swing structure. Unfortunately, I didn't develop the applet. I've pulled the jars for the applet from the cache, but there are several hundred .class files in the jars, and I don't know which one has the main method.
Is there a way to pinpoint the applet's entry point? The browser must be able to figure it out to run the applet, so that information has to be somewhere in the jar (or maybe the .idx files that were in the same directory with the jars).
Ideas appreciated.
The lifecycle of an Applet (or JApplet) is more complicated than start and run until the program is finished so there is no single main method. It will be managed by the browser (lifecycle tutorial.)
The applet class is specified by the deployment mechanism (e.g. applet/object/embed tags.) See the deployment tutorial for determining how this type is specified.
The entry class will either be in the applet tag, or JNLP for new plugin JRE 6u10+ applets. You should be able to see which one it is from the jar alone by grepping for referecnes to the Applet or JApplet classes or, say, the init()V method.
I was trying to use the wrong tool for the task.