Develop Reference

Combining .java files and exporting them as an executable jar from java code

I want to know how to export a jar file from within java code. Look at the following situation:
I have some .java files including one main class. I want to know how to pack those files and convert them to an executable jar file. I don't want to do this the traditional way by exporting the project to a jar file using eclipse built in functionality (I know how to do that). I want to know how to export the .java files and the required libraries to a jar file using java code.
Here is my ideal result: I run my own jar exporting program and it asks me to select some files. When I do select and hit 'export', it packs those files in an executable jar file. Thanks in advance and peace out.

Maybe you could try running cmd commands for creating JAR file using JAVA code.
You can create jar File in Command Prompt following these steps:
- Start Command Prompt.
- Navigate to the folder that holds your class files:
C:\>cd \mywork
- Set path to include JDK’s bin. For example:
C:\mywork> path c:\Program Files\Java\jdk1.7.0_25\bin;%path%
- Compile your class(es):
C:\mywork> javac *.java
- Create a manifest file
manifest.txt with, for example, this content:
Manifest-Version: 1.0
Created-By: 1.8.0_171 (Oracle Corporation) #your jdk version
Main-Class: mainPackage.MainClass
- Create the jar file:
C:\mywork> jar cvfm Craps.jar manifest.txt *.class
To see how can we run these commands within JAVA code, follow this link:
Run cmd commands through Java

run java program created in intellij from command line

I have a simple Java Maven program that I created in Intellij. It has Two classes Main and Read. I was able to build a jar and run it. However if I zip the source code into a folder , would I be able to compile it using command line? Something like javac ? How should I do this? Shall I run commands in Java folder in the project? Many thanks.

As far as the Java class loader is concerned, a .jar or .zip file is the same as a directory containing the the files, and .jar and .zip files are generally used to distribute compiled Java packages. Here you can read more about it.
For compiling the zip file: use the -classpath option to javac and java. We could, for example:
javac -classpath .:/users/johnr/java:/opt/jdk1.1.6/lib/classes.zip Hello.java

Create .class file from a jar file -java

I am using Java8. I have one .jar file containing .class files.
I downloaded the source code of the same .jar file. And I edited one of the file in it. It is .java file.
Now I want to compile all these .java files in the source code and create a new .jar file with .class files
Any clues?

There are many options
1. if you want to do it from command prompt then you would need to set the classpath and then either create a list of java files with package name and use it for compiling, something like this
# Linux
$ find -name "*.java" > source.txt
$ javac -classpath "${CLASSPATH}" #source.txt
:: Windows
> dir /s /B *.java > source.txt
> javac -classpath %{CLASSPATH}% #source.txt
or use build tool like Ant.
Once you have the .class files, you can use "jar" command to create a jar of the .class files
2. Use IDE - you can use any of these IDEs - eclipe, intellij, netbeans.
You need to setup a project with the java files and compile project and export as jar using class files.
I think it would work out better for you to use an IDE.

1) Compile the classes (javac command)
If you don't have any jar dependencies required at compile time, you should not need to set the classpath.
Otherwise you should specify the cp argument with.
Example (Unix way) :
javac -cp "myLib.jar:myOtherLib.jar" *.java
2) Then create a jar from these compiled class (jar command)
Example :
jar cf myjar myFolderWithCompiledClass

extract your jar to a folder and run this:
javac [folder]/*.java
read that for more info:
https://docs.oracle.com/javase/7/docs/technotes/tools/windows/javac.html

Need help building a Selenium Java Class file from cmd line

I'm trying to cmd line compile a .java selenium test script into a class file that I can run from the command line.
All of my selenium jar files and all other supporting jar and lib files are in C:\JarFiles
My CLASSPATH is set to C:\WDJarFiles*
I am working at the command line here: C:\EclipseIDEworkspace\MC3\src\Tasks
My .class files are located here C:\EclipseIDEworkspace\MC3\bin\Tasks and I'd like to be able to update them at that location.
My folder structure was set up by using Eclipse IDE so I'd like to keep the existing folder structure but now I want to be able to compile my .java files from the command line and update the .class files.
So, when I run javac like this:
javac Edit.java
It compiles OK and the .class file gets created in the same folder where I am running the javac command -- but -- I also get a huge number of other .class files in this same directory! These look like supporting class files.
I'm not sure what my cmd line javac syntax should be to:
Compile my .java file so its .class file gets updated in the C:\EclipseIDEworkspace\MC3\bin\Tasks folder.
I don't get all those other .class files created in my working folder C:\EclipseIDEworkspace\MC3\src\Tasks
Thanks for any help...

You should try the '-d' option to specify an output directory:
javac Edit.java -d ..\..\bin\Tasks
About the multiple other .class files, you probably have many nested classes into your Edit.java file?

Making a jar file run specific files first

I've made a jar file for all my classes and yes it works. Although it's not running my custom GUI. I'd like to set the jar file to run my GUI before anything else, and from there the rest of the files will be executed.
How would I do this? Thanks in advance.
When I run it through the command prompt using
java GUI
it works, but I need to do this using a jar file as I want my class files obfuscated.

I presume you jave just .class files now and you want to create a .jar file.
To run a jar file you must add -jar after the java command.
Jar files are zip files which contain the classes, possibly resources and a manifest that tells which class has the main() method.
The jar command is used to create a jar file.
jar cvfm output.jar Manifest.txt *class package1 package2
and in Manifest.txt you should have this line:
Main-Class: MainClass
After that just run:
java -jar output.jar