It's All in the Packaging.

Hello all.

Recently, I posted that if you want to build a Jython project with JDK code, it is very simple to do. However, if you want to DEVELOP your OWN Java classes, it takes a little more work. If you use an IDE to develop your code, understanding how your IDE packages your .class files is a must. Because Jython DEPENDS on knowing where your .class files are.

Understanding Java package rules will help in this are. I have found that the easiest way is to develop your Java project FIRST, then create a separate Jython project. You need to point to the directory where your .class files live.  As an alternative, you could take your Java code, package it in a .JAR file, includ it in your JYTHONPATH environment variable and you're good to go.

Creating a .JAR file is simple. A short tutorial follows:

I use IntelliJ IDEA for my coding in both Java and Jython. In my project settings, under project, I defined a global /out folder for my compiled .class files. Doing this makes it easy to create .jar files depending on your project, as I will demonstrate soon. So, currently, my folder structure is

/home/patrick/out

When IntelliJ compiles the .class files, it adds a series of sub-folders, so that it looks like this\

/home/patrick/out/production/<projectname>

Under the project name is the hierarch you created with your Java project  For me, it is

org.ppalczewski.<project>.<source1>.<so on>

So, in the end, my /out folder looks like this:

/home/patrick/out/production/<projectname>/org.ppalczewski.<project>/<source1>/<source2>/ etc

Wow, that's a lot of typing. But I only want to create a .jar that shows the hierarchy from org.ppaczewski dowm. I can do this two ways. First, I can navigate to my <projectname> folder (i.e. /home/patrick/out/production/<projectname>).

Then, I type this command to build my .JAR file:

jar cvf <project>.jar .

This will recurse from the <projectname> folder down and include all .class files. The switches are c(create), v(verbose), f(jar file name)

I have a root jarfiles folder that holds all of my jar files. I can navigate to this folder and type the following:

jar cvf <project>.jar -C /home/patrick/out/production/<projectname>/ .

This will do the same thing, and it retains your fully qualified package name structure (for me: org.ppalczewski.<project>.etc,etc).

It is very important to include the ending slash (or backslash in Windows). If you don't, you may get unexpected results. you can verify your package qualified name by

jar tf <jarfile>.jar

and this will list the .class files you have in your project.

So, after I have built my .jar file, and included this in my JYTHONPATH (you MUST include the actual name of your .jar file also), I can now fire up my Jython interpreter and test to see that it works.

In my code, I type this:

import org.ppalczewski.<project> as project

Now I have access to any classes I may have created.

To me, this makes it easier than having worry about whether Jython can see the .class files or not. 1. Build Java code. 2. Package in .jar file. 3. Import into Jython 4. Enjoy!

Then, for distribution, have the .jar file available and that's it.

Say you alread have a .jar file and you updated the code in your project? Do you need to delete the jar file and create a new one? No. Use the jar command's updatte feature, which will recreate the .jar file for you, adding any new files or updated code.

jar uvf <jarfile>.jar [-C <path>/<to>/<production>/] .

If I am able, I will create a blog with a simple project demonstrating this.

That's it for today. Happy coding!

Hybrid Jython/Java projects in IntelliJ?

The post title is a pretty good question. The answer is: It's extremely difficult.

I will explain:

If you are pulling from extablished Java packages (JAR files), it's very easy.

However, if you are developing YOUR OWN Java classes, this is where the roadblocks start popping up. What I have found is that it's easier (in the long run) to develop you own classes in a Java project, and package them into a JAR file. Then create a separate Jython package that points to the JAR file. You can actually add it as a library in your Project settings,
The reason for this is that IntelliJ actually stores all your .class files in an output directory you must specify. So,m when you open up a .py file, it can see your code internally, but the actual .class files are somewhere else. And if you use a package structure, Jython cannot see the .class files, so it breaks the code.

For the really adventurous, you need to navigate to your output folder, call the java class with the FULLY qualified name, and it will work.

Much better to simply start a Jython project abnd point it to your output folderwhere your .class files are stored. Even easier to do the Java code, bundle it in a JAR and use Jython to call it with the qualified package name.

My ealier post on setting up IntelliJ was to work on Jython ITSELF, not for general Jython development.

I have also discovered that if you use IntelliJ's GUI builder to do your forms, Jython has a lot of trouble with that also. Why> IntelliJ stores the attributes (preferredSize, windowClosing, etc.) in its own .class files, contained in a com.intellij package. To pull up the form via Jython, you need to reference theis package. If you know your Jaa forms, and can do it via code, this way with alleviate the stress of Jython trying to find the particulars of your form to display.

If you separate your projects as I have stated above, you should be okay, as you can import the com.intellij packages into jython with hno problem and the form will be called correctly by the JVM your are using.

If you want to test your code via the command-line outside of IntelliJ, you can. Naviate to the folder ABOVE source folder and call it with the qulalified path name. Here's an example:

Let's say you have the following directory structure:

/home/patrick/myproj/mycode

I use a global out folder in IntelliJ, so it looks like this:

/home/patrick/out/production/myproj mycode


I create a test.java, and compile it. It puts the class files in the /mycode folder. Then I navigate to /home/patrick/out/production and call Test like so:

java mycode.Test

It will run. You need to match the package structure in your source file to properlyt call the class.

Lets sayyou have no package name. Navigate to the folder containing the .class file. Then you call Java with the -classpath option (listing your folder) and the class.

java -classpath /home/patrick/myproj/mycode Test

That's is for now. Fell free to comment, or provide correction. I still have a lot to learn. if you have successfully developed a JythonJava project using your own classes, let me know how and I will update this post.

Thank you and happy coding!