I know that .jar files are basically archives as well as being applications. What I'm asking is how can I store data(actual files not just strings) packed inside my program? I want to do this within my Java code.
The reason for this if your wondering is that I'm producing a server mod of a game. The server starts and creates all the level data and I want to store all these file inside my .jar app.
Yes you can do this.
Non-code resources in a JAR file on the classpath can be accessed using Class.getResourceAsStream(String). Applications routinely do this, for example, to embed internationalized messages as resource bundles.
To get your file into the JAR file (at project build time!), just copy it into the appropriate place in the input directory tree before you run the jar command. Build tools such as Maven, Gradle, etc can automate that for you.
Is there a way to add files to the archive within the app?
In theory, your application could store files inside its own JAR file, under certain circumstances:
The JAR has to be a file in the local file system; i.e. not a JAR that was fetched from a remote server.
The application has to have write access to the JAR file and its parent directory.
The application must not need to read back the file it wrote to the JAR in the current classloader; i.e. without exiting and restarting.
The JAR must not need to be be signed.
The procedure would be:
Locate the JAR file and open as a ZIP archive reader.
Create a ZIP archive writer to write a new version of JAR file.
Write the application's files to the writer.
Write all resources from the ZIP reader to the writer, excluding old versions of the applications files.
Close the reader and writer.
Rename the new version of the JAR to replace the old one.
The last step might not work if the initial JAR is locked by the JVM / OS. In that case, you need do the renaming in a wrapper script.
However, I think that most people would agree that this is a BAD IDEA. It is simpler and more robust to just write regular files.
The other answers have provided some good strategies, but I am going to suggest going in a somewhat different direction.
This game supposedly has graphics and is a desktop application. It is most easy to distribute desktop applications from a web server.
If both those things are true of your game, then look into using Java Web Start to deploy it.
JWS offers APIs not available to other apps. & one of particular interest to this problem is the PersistenceService. The PersistenceService allows for small amounts of data to be stored and restored by an app. (even when it is in a sand-box). I have made a small demo. of the PersistenceService.
The idea would be to check the PersistenceService for the application data, and if not found, use the data in the Jars. If the user/application alters the data, write the altered data to the PersistenceService.
JWS also offers other nice features like splash screens, desktop integration, automatic updates..
This is not possible. You however can look into embedded databases for your usecase. Java 6 comes with JavaDB. If you doesn't want to use it then you can find more here http://java-source.net/open-source/database-engines
I would recommend that you consider having two JARs: one to store your application's class files and another JAR to store the user data. If you do not have two separate JARs, then you will have difficulties obtaining a write lock from the Operating System (since you would be trying to overwrite the JAR containing your program while java is reading it).
To create a JAR, use the java.util.jar.JarFile class. There is also another question on stackoverflow which describes how to create/write a JAR file.
Don't do this. A jar file is a source of application classes and resources, not a file system. You wouldn't try to save files into a exe, would you?
By creating a file in the Source Packages (ex: /src/resource/file.txt) its contents can be read using Class.getResourceAsStream(String)
This is a working implementation of the following answer
InputStream is = Class.class.getResourceAsStream("/resource/file.txt");
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
StringBuilder sb = new StringBuilder();
String line;
while((line = br.readLine()) != null) {
sb.append(line).append("\n");
}
System.out.println(sb.toString());
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.
If I have a resource file (mydata.txt) in resources folder (set up as another source folder) of my application. This mydata.txt eventually would be packaged inside root of a jar file (.war) to be deployed to some application server (Tomcat, Jetty, WildFly).
File mydata.txt has some crucial data needed to the application, and this file shall be appended by the application.
To get a file from jar I can use getClass().getResourceAsStream("/mydata.txt") - thus I get this file as InputStream. But there is no way I can get this file as OutputStream and write to it.
All solutions with getClass().getResource() - returning URL are discouraged, getResourceAsStream is always recommended, but it allows only reading, not writing/updating/appending the file.
getClass().getProtectionDomain().getCodeSource() solution is also discouraged to get (write) access to the file.
I could create some file in a temporary directory on Tomcat Server (System.getProperty("java.io.tmpdir") and write to it, but it is nonsense because this file contents is crucial for the application (to write it to tmp dir), besides I need to append file, not create a new one and write to it.
Also, I am not sure that writing to any other directory (other than tmp) of application server is a good idea (please correct me if I am wrong here).
So I come to the conclusion that it is not recommended to save any data to a file in enterprise application, so I shall always use a database instead?
In short: Yes. Beside all you mentioned (which is all correct) the biggest problems are
concurrent access
transaction handling
which both a database serves perfect and with a file approach is just a pain in the ****
In addition to that especially an application server provides you with configuration of connection (and pools) to data sources of any kind, which is really handy in a production environment.
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'm using the Netbeans IDE, and I'm currently using a GlassFish server.
What I want to do is write to a file.
I looked at some pages, and the code I have now (that is not working as far as I know) looks like:
File outputFile = new File(getServletContext().getRealPath("/")
+ "TheFile.txt");
FileWriter fout = new FileWriter(outputFile);
fout.write("The Content");
fout.close();
This is my project's structure:
Also where will the file get placed?
Edit:
I forgot to mention there are some other folders below the ones in the picture: Test Packages, Libraries, Test Libraries and Configuration Files. However I don't think the file would get placed there.
Edit (newest):
I found out the file is stored in the /build/web folder, but this is not appearing in Netbeans. Even after I restarted it.
As you've coded, the file will be placed in public web root. That's where getRealPath("/") will point to. To be precise, it's the folder named Web Pages as in your screenshot. As an exercise, do the following to figure the absolute path, so that you can find it by OS disk explorer.
System.out.println(file.getAbsolutePath());
I don't do Netbeans, but likely you need to refresh the folder in your IDE after the write of the file so that it appears in the listing in the IDE. Click the folder and press F5. This is at least true for Eclipse.
That said, this approach is not recommended. This won't work when the servletcontainer isn't configured to expand the WAR on disk. Even when it did, you will lose all new files and changes in existing files when the WAR is been redeployed. It should not be used as a permanent storage. Rather store it on a fixed path outside the webapp or in a database (which is preferred since you seem want to reinvent a CMS).
Note that this is in no way guaranteed to work in all web containers or through restarts and will most likely be overwritten by a redeployment.
If you want to be able to allow your user to update content, you need to store the new content somewhere and have a servlet or a JSP-page or a facelet retrieve the new content from the backing storage and send it to the browser.
See the documentation for getRealPath. It returns you the location on the disk for something specified with a URL.
I'm guessing your file is in the root of your web application on the disk within Glassfish (where the WAR file is extracted). I don't know enough about Glassfish to say where that will be.
Also, note you are using string concatenation to create the file name, so if the getRealPath call doesn't return a String with a "/" on the end, then you might be creating a file in the parent directory of your web app. Perhaps best to use a File object for the parent directory when creating the File object for the actual file. Check out the File API.
I'd recommend creating the file outside of your web app. If you redeploy your WAR file then you might delete your file, which probably isn't what you want.
Being in a servlet makes little difference to the fact that you want to output a file. Just follow the standard file APIs as a starting point. Here's a tutorial.
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