I read and searched almost everywhere, yet i have no answer.
I have a project with multiple .java files, and i need to export them as a single .jar file.
One of the main questions is based on the fact that i don't have a main class.
What can i do to go through that ? Shall i create a main but never run it? Or there's any way around?
Offtopic ( might be usefull): i want to do this in order to use the jar file in IKVM
Thank you!
You do not need a main method to create a jar. There are many such jars out there such as utilities packages. They don't contain any code that would make sense to execute on it's own since it only contains code that makes your application easier to write.
First compile your code using Netbeans or command line javac utility. This will give you .class files.
Now for creating the jar... You can simply create the jar (which is basically a glorified zip archive) by using the command-line jar tool.
jar -cvf my archive.jar myprogram/
Make sure that the file path within the jar archive match the package name of the classes. It is not uncommon to accidentally get an extra layer of directories.
You probably should have searched stackoverflow first since how-to-create-a-jar-file-in-netbeans seems to cover exactly what you're looking for.
Do you want to use the jar as a external library or a program itself?
If it will be a external library, you don't need a main class. In eclipse you can export as a jar file (select classes-> right click-> export as jar).
If it will be a program itself, then you need a main class.
You really need to create main class file, write code in function main(String args[]) which use your java classes and compile it by javac.
Related
I'm trying to use VS Code with java, but I have an issue.
As a student, my teacher gives me a file named Clavier.class.
I have already wrote a programm with another IDE, and when I execute it in the command of Windows, it works without any problem. But, when I put this programm in VS Code, it doesn't recognize Clavier.saisirInt, which is a static method in Clavier.class. I guess that VS Code can't use a class which is in a File.class, but is there a way to make it works ?
Here is an image of my workspace and you can see the error at the bottom
I assume your lib/ folder is placed onto the execution classpath. If this is the case, that's where compiled class files should go, not next to your sources
Otherwise, you'll need to inspect the java command that actually runs your code to see what/if the -cp argument is set to, or include those class files similar to how the documentation shows for JAR files (which are just zipped packages of class files, and honestly what the teacher should provide instead)
By default, VS Code will reference all JAR files in workspace's lib directory using the glob pattern lib/**/*.jar
And so, you need to adjust this to include lib/*.class after moving your files there
I have a problem with finding all the external libraries that a .jar file uses. My .jar file is very big, and manually decompiling it and going through every class, checking all the used paths is impossible. I wonder if there is a way or a tool that would go through a .jar file, and list all the external paths/links to classes that are not in the .jar file?
P.S: I'm not asking "what is the best tool to do so?", I just need to know how to get all the external paths a .jar file uses, without manually decompiling it.
Try this :
Extract the jar contents
Do a directory search for *.class piped to a text file.
Filter out inner and anonymous classes. (Class files names with $)
Write a small program that will simply loop through your list and load the class definition (Class.forName() should be enough)
Run the jar with option -verbose:class piped to a text file
Once your program is completed, you will have a full list of classes loaded from respective jars in the piped file
Filter out rt.jar contents for a more cleaner list
I'm not sure if -verbose:class works with obfustcated code, logically I think it should be fine.
I have a Jar file that has the a few packages.
I want to import the commons library and within Eclipse that's pretty simple.
However when I export the jar file, and run it, it is not able to find the commons library and therefore unable to run. I want to know if I have to move the commons jar files to the exact same directory (within the package)? Or if there is something I can add to the import lines to make it work?
I also want to make this jar file able to be sent to people and used by anyone without having to get them to modify anything on their computer
you need to include jars in your classpath if you are running on command line (Here is an example of this)
if you want it to all be neatly wrapped in one jar consider looking at OneJar. (oneJar example) or JarJar.
I have a Java application that was converted to an .exe with launch4j. For several reasons I need to get access to the class files of the application.
The first thing I tried was unpacking the exe with 7zip. That way I get a handful of class files, but definately not the whole application packed in the exe (the class files seem to belong to launch4j).
What other options are there?
You can use something like this to extract the JAR from the Launch4j executable:
http://www.nirsoft.net/utils/resources_extract.html
Typically the executable packages necessary JAR's as executable resources and then looks for a JDK on the path to execute.
Once you get the JAR file you should be able to decompile it.
You cannot get access to class files. Exes are created, So that nobody can get access to your code.
If somehow , you are able to get access to jar files then you can decompile them to get the code and make changes.
If there's one thing that annoys me about Java it's that you can't double-click a class file so as to run. I assuming there's an entry in the registry that has to be edited to do this but I haven't a clue.
So, as it says on the tin. Does anyone know how to associate Java class files to run on double-click on Windows (I aiming for Windows 7 here but I'm sure there'd be no difference in the three most latest releases)? It would make my life (and I'm sure many other people's) much easier!
Udpate: I've seen answers relating to making a JAR out of the class in question and running it that way. However useful, that is not exactly what I'm looking for here. I'm effectively looking for Windows itself to invoke java with the class on double-click, with the correct arguments.
if classpath doesnt matter too much, easily done with a simple batch file runjava.bat or so that is associated with .class files in the explorer (via right click >> open with..)
#echo off
REM change to folder where the class file resides
cd %~d1%~p1
REM execute the class by calling its name without file extension
start java %~n1
The double-clickable JAR solution is the most common plain Java distribution method. There'd be a number of issues with trying to execute .class files directly, with the classpath the one that pops first to mind.
That said, if you wanted to support the very simplest possibilities in your development environment, you could conceivably implement a script that
inspected the .class file for the full class name (including package and inner class name)
walked up the directory tree to the root of the file's class path
(optionally included any common lib directories in the classpath)
invoked Java for the determined class
Then you could register your shiny script as a handler for .class files. But since you're in the development environment, aren't you happier with your IDE doing that?
For a .class file to run, needs in first place to have "something" to do, that is, that .class should contain a main method. Not all the .class do have one.
One thing you can do, is to wrap your app ( a number of .class files ) inside a jar file.
For short, you just need in addition to your classes a manifest file that says, where the main method is:
jar -cmf yourmanifestfile.mf doubleClickApp.jar *.class
And that's it, the doubleClickApp.jar is now executable with a "doubleClick" gesture.
When you install the Java Runtime Environment, it registers .jar files as an association in Windows. If you double-click on a .jar file, it will open it using Java. For this to work, you need to make sure you have a manifest defined that points to the class to run. Your class file to be run must have a main method that will be called.
Let's assume you have a class named 'com.TheClass.class' on disk. If you want to have this able to run with double click, create a file in a new directory called META-INF/manifest.mf. Put this into it:
Manifest-Version: 1.2
Main-Class: com.TheClass
Zip (or use the jar command) both your class up with this manifest directory and file. Rename it to mine.jar. Double click on it and it should launch your class with the Java runtime.
http://justaddhotwater.webs.com/javaexec.htm
This software makes it possible to run your Java classes by double-clicking them.(Windows ONLY).
The easiest way that I have found was creating a shortcut on the same folder than the .class file. Then right click on it and go to properties. Change the field Target to java NameOfClass, finally double click the shortcut :)