Question

My program has a function that read/write file from resource. This function I have tested smoothly.
For example, I write something to file, restart and loading again, I can read that data again.

But after I export to jar file, I faced problems when write file. Here is my code to write file:

URL resourceUrl = getClass().getResource("/resource/data.sav");
File file = new File(resourceUrl.toURI());
FileOutputStream output = new FileOutputStream(file);
ObjectOutputStream writer = new ObjectOutputStream( output);

When this code run, I has notice error in Command Prompt:

So, My data cannot saved. (I know it because after I restarted app, nothing changed !!!)

Please help me solve this problem.

Thanks 🙂

Answer 1

You simply can’t write files into a jar file this way. The URI you get from getResource() isn’t a file:/// URI, and it can’t be passed to java.io.File's constructor. The only way to write a zip file is by using the classes in java.util.zip that are designed for this purpose, and those classes are designed to let you write entire jar files, not stream data to a single file inside of one. In a real installation, the user may not even have permission to write to the jar file, anyway.

You’re going to need to save your data into a real file on the file system, or possibly, if it’s small enough, by using the preferences API.