I wrote a little Java app for analyzing .csv files. Now I want to keep reading from and writing to a .txt file, which acts similar to a mini-database. For this purpose I simply added the .txt in my project and used the Files.readString(Path) and Files.write(Path path, byte[] bytes) methods.
When I do this in IntelliJ I have no problems but as soon as I build/export the file with Maven and started with the created launcher the app didn't work because the project structure / file organization isn't the same anymore.
I also tried to just add the .txt file to the exported folder afterwards but even then I couldn't manage to implement a relative path to the file.
I'm still relatively new to programming and it's just a small app so I don't think mySQL would fit my needs. I've also read that I could store the data in a property file but I don't know if that would be the right way to archive what I want. Certainly it must be possible to somehow keep a .txt for reading and writing in your exported project. Does someone have an idea?
If you use a ยด*.txt` file for storing, that file cannot be inside the jar because the jar cannot change its contents while running.
You need to put the file somewhere else, either at some dedicated location (let the user choose/configure one), or next to the jar. To figure out your own execution path, you can use
How to get the path of a running JAR file?
Maven is one tricky tool. You need to go to the pom file and add the resource.
Unable to add resources to final jar for maven project in Intellij.
-I hope this helps
Trader
Related
I'm kinda new to spring and web development as a whole.
My question is:
When you build a spring boot project (using Maven) into jar file and deploy it via Docker, everything is in one jar file. How can you access your resources (css, js, images, html...) if you want to edit something? Like change something in css file or add something to html page. Is it even possible? Or do you have to build a new jar file everytime, when you need to change something (in frontend)? Also, when there are being uploaded some images or other files, where are they stored? This stuff is very confusing for me and i can't find any related books or help at all.
Thanks for help!
when you package any java program it is nothing but a zip file. Based on what kind of package it is, you wither name it as a Jar or War.
Jar == Java archive
War == Web archive
Now, given the fact that jar and war both are essentially a zip archive, it gives you flexibility to extract and modify them just like any other zip file.
On windows, I think softwares like 7zip let you update the jar inline. I have done it multiple times, especially when I wanted to change application.properties alone on cloud machines, and no other code changes were required. In such cases, building the whole jar and transferring it again to cloud machine could be time consuming. So I would just extract the contents, update whatever I want to, and rezip the package.
Here is the commands you can use -
jar xf jar-file
This should extract the files into a directory.
This SO thread will guide you towards creating jar files.
Something like jar cf myJar.jar ** should be enough to generate a jar file IMO, but syntax might vary.
The jar file is actually just a zip file containing all the files and classes of your application, so technically you can change files in it like any other zip archive. Best practice is to build the jar file using Maven or Gradle from source every time you need something changed.
It's good practice to keep the source in version control using Git, and tag each build in the git repository - that way you can easily keep track of changes to the jar file by looking at what's in git at the time of the build.
I'm create an application that is going to be run on Windows, Mac OX and Linux. I have a properties file storing user settings which need to be read and changed on the fly.
A JAR file is compressed and is not meant to be changed on the fly which means I should write to an external file.
I'm using :
new FileInputStream("database")
new FileOutputStream("database")
How do I create a URL which is going to be consistent throughout all three operating systems. The JAR is run as an application on the desktop and I would like the file to be stored somewhere discrete.
I've tried reading from a local file in the same package as this class :
this.getClass().getResourceAsStream("database")
This works however I can't seem to create an output stream to write to the same file but this would be breaking the rule of changing a JAR file on the fly.
There are plenty of good reasons for which you should not do this, off the top of my head:
GetResourceAsStream does not necessarily get the file from the JAR itself. You coincidentally got it from there because the Jar was the first or the only element in the class path.
Writing a file in your own Jar could break the JAR signature if you are going to sign it.
The database could need to be backed up; in this case you may want to back it up separate from the code (the code could be upgraded when restoring the database).
Hope this helps.
I am writing a program which is dependent on saving to a resource folder that is exported with the jar. I have a source folder titled "resources/inputs" and it exports correctly. I can load from it which is great, but the problem is, when I use:
getClass().getResource(path);
I cannot save to the path returned. I need to be able to save to it and I was wondering, is there any way I can save to this resource folder (or to some other folder existent in the same directory as the jar) no matter where the user has saved the jar file?
The error I get is a FileNotFoundException and the background I've read on it is that since jar triggers java "read-lock" you can only ever read from a jar and can never write to it? Not sure if that is accurate or not, but if it is, how can I work around this using an external folder?
I've never tried this, but its probably having a hard time because the you need to use specialized classes to access files within a jar file (which is a zip file with a different extension). Google "JarEntry" and see if that points you in the right direction.
Does this answer your question
I'm learning java and am currently trying to develop a simple application. My question is can you store data about settings, etc in a text file internal to a .jar? If so how would you go about accessing this within java? Sorry if this is a really stupid idea.
InputStream is = this.getClass().getResourceAsStream("/data/file.txt");
The resources you are getting need to be on the classpath
Yes you can, and it's not a stupid question we all need to start somewhere.
There are two parts to your question:
Adding a data/text file to a .jar - (using ant to jar it:) add "fileset dir=..." to the jar target, where dir is set equal to the directory that has the data/text file. Refer to How can I include data text files in a jar using Ant?
Accessing that data/text file from within the java code - you need to use a ClassLoader and getResourceAsStream. Refer to Loading files in JAR in Tomcat using getResourceAsStream
Also, please take a look at https://github.com/gitjonathan/turbo-sansa, I have a working version up on it.
Can you store data inside a .jar?
Read-only data can be stored inside a JAR file. You can read such data using getResourceAsStream(...) if the JAR is on the classpath, or by using the standard JAR file API class if it is not on tle classpath.
But storing update-able data in a JAR file is problematic:
In a lot of circumstances it is impossible; e.g. because the JAR file is read-only or was downloaded on the fly.
In all other cases it would be very awkward, because the standard JAR file API class does not support update in place. (You would need to create a new ZIP file, copy across the old content apart from the file you are updating, add that file, and then rename the resulting file.)
I just realised that I cant use files from outside a jar archive. If thats the case then when I deploy apps that need other documents, say an xml file, do i send the xml alongside the app or there is a way out..
Thanks
I'd suggest that you simply include the required resources within the .jar file. You can have any type of files in there, including .xml-files.
Related questions:
How do I create a jar file, which includes xml and html files?
How do I read a resource file from a Java jar file?
adding non-code resources to jar file using Ant
How to bundle images in jar file
If you really prefer to load "external" files you'll have to be more clear about the problems of opening them outside of the jar file.
But this does not work if you also want to "write" to one of those files!!! If you only want to read, put everything in there. The convention is to create a package called resources in the root of you source code ("src" for example (I use Eclipse)), and just put everything in there, and then use class.getResourceAsStream(). But if you want to write to a File, for example you want persistence for User's options or other stuff, you're gonna need to write from within the .jar, to a File outside the jar, which has a lot of permission considerations and stuff, but It's possible. use System.getProperty("java.class.path"), and you can write files just next to your jar File...