I need to store data into files inside .jar file and read it again.
I know that I can use Class.getResourceAsStream() method but it returns an InputStream that I can read from. But I look for a way to write.
I need to store data into files inside .jar file and read it again
No you don't.
Instead store the 'default' file inside the Jar. If it is changed, store the altered file in another place. One common place is a sub-directory of user.home. When checking for the file, first check the existence of an altered file on the file system, and if it does not exist, load the default file.
Note that it is generally better to describe the goal, rather than the strategy. 'Store changed file in Jar' is a strategy, whereas 'Save preferences between runs' might be the goal.
Related: What is the XY problem?
This is not really supported. In principle, you could operate on the jar file, but there's no guarantee the new contents would be correctly loaded. Let your build tools manage the jar file -- and choose something else for persistent storage managed by your program itself. Like a file.
It is unlikely that you can change a loaded jar safely. Changing it while it is being used is not a good idea.
If you want to do this, use a plain file system directory and add/remove files from it. Even this may not work as you expect.
You can manipulate any jar file using the package java.util.jar (or indeed just java.util.zip). As files inside a jar will be compressed, this isn't the most time efficient way for you to store data.
You should probably use a directory somewhere else (e.g. System.getProperty("user.home") + "/.myProgram") or see java.util.prefs.
Class.getResource() returns a URL. Theoretically, you can use this URL to create your InputStream and OutputStream. But in most cases, the generated JAR is a read-only file (or archive). So your application might trip when trying to use it.
Related
Summary:
I have a program I want to ship as a single jar file.
It depends on three big resource files (700MB each) in a binary format. The file content can easily be accessed via indexing, my parser therefore reads these files as RandomAccessFile-objects.
So my goal is to access resource files from a jar via File objects.
My problem:
When accessing the resource files from my file system, there is no issue, but I aim to pack them into the jar file of the program, so the user does not need to handle these files themselves.
The only way I found so far to access a file packed in a jar is via InputStream (generated by class.getResourceAsStream()), which is totally useless for my application as it would be much too slow reading these files from start to end instead of using RandomAccessFile.
Copying the file content into a file, reading it and deleting it in runtime is no option eigher for the same reason.
Can someone confirm that there is no way to achieve my goal or provide a solution (or a hint so I can work it out myself)?
What I found so far:
I found this answer and if I understand the answer it says that there is no way to solve my problem:
Resources in a .jar file are not files in the sense that the OS can access them directly via normal file access APIs.
And since java.io.File represents exactly that kind of file (i.e. a thing that looks like a file to the OS), it can't be used to refer to anything in a .jar file.
A possible workaround is to extract the resource to a temporary file and refer to that with a File.
I think I can follow the reasoning behind it, but it is over eight years old now and while I am not very educated when it comes to file systems and archives, I know that the Java language has evolved quite much since then, so maybe there is hope? :)
Probably useless background information:
The files are genomes in the 2bit format and I use the TwoBitParser from biojava via the wrapper class TwoBitFacade?. The Javadocs can be found here and here.
Resources are not files, and they live in a JAR file, which is not a random access medium.
I need to store data into files inside .jar file and read it again.
I know that I can use Class.getResourceAsStream() method but it returns an InputStream that I can read from. But I look for a way to write.
I need to store data into files inside .jar file and read it again
No you don't.
Instead store the 'default' file inside the Jar. If it is changed, store the altered file in another place. One common place is a sub-directory of user.home. When checking for the file, first check the existence of an altered file on the file system, and if it does not exist, load the default file.
Note that it is generally better to describe the goal, rather than the strategy. 'Store changed file in Jar' is a strategy, whereas 'Save preferences between runs' might be the goal.
Related: What is the XY problem?
This is not really supported. In principle, you could operate on the jar file, but there's no guarantee the new contents would be correctly loaded. Let your build tools manage the jar file -- and choose something else for persistent storage managed by your program itself. Like a file.
It is unlikely that you can change a loaded jar safely. Changing it while it is being used is not a good idea.
If you want to do this, use a plain file system directory and add/remove files from it. Even this may not work as you expect.
You can manipulate any jar file using the package java.util.jar (or indeed just java.util.zip). As files inside a jar will be compressed, this isn't the most time efficient way for you to store data.
You should probably use a directory somewhere else (e.g. System.getProperty("user.home") + "/.myProgram") or see java.util.prefs.
Class.getResource() returns a URL. Theoretically, you can use this URL to create your InputStream and OutputStream. But in most cases, the generated JAR is a read-only file (or archive). So your application might trip when trying to use it.
I need to store data into files inside .jar file and read it again.
I know that I can use Class.getResourceAsStream() method but it returns an InputStream that I can read from. But I look for a way to write.
I need to store data into files inside .jar file and read it again
No you don't.
Instead store the 'default' file inside the Jar. If it is changed, store the altered file in another place. One common place is a sub-directory of user.home. When checking for the file, first check the existence of an altered file on the file system, and if it does not exist, load the default file.
Note that it is generally better to describe the goal, rather than the strategy. 'Store changed file in Jar' is a strategy, whereas 'Save preferences between runs' might be the goal.
Related: What is the XY problem?
This is not really supported. In principle, you could operate on the jar file, but there's no guarantee the new contents would be correctly loaded. Let your build tools manage the jar file -- and choose something else for persistent storage managed by your program itself. Like a file.
It is unlikely that you can change a loaded jar safely. Changing it while it is being used is not a good idea.
If you want to do this, use a plain file system directory and add/remove files from it. Even this may not work as you expect.
You can manipulate any jar file using the package java.util.jar (or indeed just java.util.zip). As files inside a jar will be compressed, this isn't the most time efficient way for you to store data.
You should probably use a directory somewhere else (e.g. System.getProperty("user.home") + "/.myProgram") or see java.util.prefs.
Class.getResource() returns a URL. Theoretically, you can use this URL to create your InputStream and OutputStream. But in most cases, the generated JAR is a read-only file (or archive). So your application might trip when trying to use it.
I am doing a project in java and in that i need to add and modify my
text file at runtime,which is grouped in the jar.
I am using class.getResourceAsStream(filename) this method we
can read that file from class path.
i want to write into the same textfile.
What is the possible solution for this.
If i can't update the text file in jar what other solution is there?
Appreciate any help.
The easiest solution here is to not put the file in the jar. It sounds like you are putting files in your jar so that your user only needs to worry about one file that contains everything related to that program. This is an artificial constraint and just add headaches.
There is a simple solution that still allows you to distribute just the jar file. At start up, attempt to read the file from the file system. If you don't find it, use default values that are encoded in you program. Then when changes are made, you can write it to the file system.
In general, you can't update a file that you located using getResourceAsStream. It might be a file in a JAR/ZIP file ... and writing it would entail rewriting the entire JAR file. It might be a remote file served up by a Url classloader.
For your sanity (and good practice), you should not attempt to update files that you access via the classpath. If you need to, read the file out of the JAR file (or whatever), copy it into the regular file system, and then update the copy.
I'm not saying that it is impossible to do this in all cases. Indeed, in most normal cases you can do it with some effort. However, this is not supported, and there are no standard APIs for doing this.
Furthermore, attempts to update resources are liable to cause anomalies in the classloader. For example, I'd expect resources in JAR files to not update (from the perspective of the application) until the application restarted. But resources in exploded JAR files probably would update ... though new resources might not show up.
Finally, there are cases where updating a resource is impossible:
When the user doesn't have write access to the application's installation directory. This is typical for a properly administered UNIX / Linux machine.
When the JAR file is fetched from a remote server, you are likely not to be able to write the updates back.
When you are using an arbitrary custom classloader, you've got no way of knowing where the actual bytes of an updated resource should be stored, and no way of storing them.
All JAR rewriting techniques in Java look similar. Open the Jar file, read all of it's contents, and write a new Jar file containing the unmodified contents (and the modifications you whished to make). Such techniques are not advisable for a Jar file on the class path, much less a Jar file you're running from.
If you decide you must do it this way, Java World has a few articles:
Modifying Archives, Part 1
Modifying Archives, Part 2
A good solution that avoids the need to put your items into a Jar file is to read (if present) a properties file out of a hidden subdirectory in the user's home directory. The logic looks a bit like this:
if (the hidden directory named after my application doesn't exist) {
makeTheHiddenDirectory();
writeTheDefaultPropertiesFile();
}
Properties appProps = new Properties();
appProps.load(new FileInputStream(fileInHiddenDir));
...
... After the appProps have changed ...
...
appProps.store(new FileOutputStream(fileInHiddenDir), "Do not modify this file");
Look to java.util.Properties, and keep in mind that they have two different load and store formats (key = value based and XML based). Pick the one that suits you best.
If i can't update the text file in jar what other solution is there?
Store the information in any of:
Cookies
The server
Deploy the applet using 1.6.0_10+, launch it using JWS and use the PersistenceService to store the information. Here is my demo. of the PersistenceService.
Also, if your users will agree to a trusted applet (which seems overkill for this), you might write the information to a sub-directory of user.home.
I am attempting to store the change made to my application's properties. The .properties file is located in resources package, which is different from the package that contains my UI and model.
I opened the package using:
this.getClass().getClassLoader().getResourceAsStream("resources/settings.properties")
Is there a functional equivalent of this that permits me to persist changes to the Properties Class in the same .Properties file?
In general, you cannot put stuff back into a resource you got from the classloader:
Class loader resources are often read-only; i.e. held in read-only files / read-only directories.
If you got the resource from a JAR file, JAR files are not simply updateable. (To "update" you need to extract the old JAR's contents and create a new JAR with the updated contents. It is all to do with the structure of ZIP files ...)
In some cases, the class loader resource will have been downloaded on-the-fly, and there is no way to push changes back to the place where you downloaded from.
Even if you can update a resource you got from the classloader, it is a bad idea / bad practice.
Doing this "pollutes" the clean application installation with a user's preferences. Among other things, this means that the installation cannot be shared with other users (unless you handle preferences for multiple users ...).
There are security issues with having applications installed as writeable so that embedded preferences can be updated. Think viruses! Think one user who might be inclined to trash another user's preferences!
There are administration issues with having user-specific copies of applications. And if the user has to install his own copy of an app, there are potential security issues with that as well.
There may be technical issues with file locking or caching on some platforms that either get in the way of (safe) updates or make it difficult for an application to load the updated resource without a restart.
Finally, this is NOT the way that system administrators (and educated users) expect software to behave. Java applications should deal with user preferences in the expected way:
You can use the Java Preferences API.
You can write a Properties file containing the preferences to an OS-appropriate user-writable directory.
On Windows, you could use a Windows-specific API to store the preferences in the Windows registry, except that this makes your application Windows dependent. (I can't see any real advantage in doing this, but I am not a Window expert.)
When you wrap your app up as a JAR file, your properties file will be one (possibly compressed) file within that JAR, and it would be a bad idea to try to write to your own JAR.
getResourceAsStream() is meant to open resources for reading, and these can be anywhere on the classpath. You can't write to URLs or inside JARs, you can only write to files, so it doesn't make sense to give you the same API for output.
Find yourself a directory you're allowed to write into, and write your properties there.
It may be a good idea to copy your properties from your installation classpath (possibly inside a JAR) directly out to a file if it doesn't yet exist, as a first operation upon application startup. This will give you a properties file you can write to, yet the master copy of this properties file will come from your project deliverable.
It sounds like you want to store user preferences. Consider using the Java Preferences API for that.
In addition to Carl's answer, if you're going to read and write to this file frequently, and expect that your application will expand in scope, consider whether to go one step (or several steps) further and use a file-based database like SQLite. There are a few JDBC wrappers for SQLite that would allow you to go beyond the basic string key-value lookup that the Java Properties interface provides.
even though writing the file into resources is not good practical, we still need to do it when our application only run in IDEA locally without deployment, then we can do it as below:
URL resource = Thread.currentThread().getContextClassLoader().getResource("settings.properties");
String path= resource.getPath();
OutputStream outputStream = new FileOutputStream(path);
//outputStream write