Updating a properies file in a .jar file

Hi
I have an application that reads a properties file from a .jar file using the getSystemResourceAsStream method on the ClassLoader class. What I would like to be able to do is to change values in this properties file when the application exits so the next time into the application the last used values for certain text boxes are remembered from last time. Can anyone suggest a way to achieve this. I can write the properties file out using the FileWriter class and this works but I read it is not a good idea to use these classes for this purpose.
Thanks in advance

Those .properties files can perfectly be writting using a FileOutputStream
(not a Writer). Updating a .properties file in a .jar file isn't possible
without rewriting the entire .jar file.
Your scenario should work fine: if the .properties file doesn't exist, get
a "prototype" from the .jar file and store it as an independent file. Update
this file using a FileOutputStream ad lib.
kind regards,
Jos
ps. if you don't like this scenario, you could have a look at the Preferences class.

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How to read a file inside the JAR file

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I want to save some preferences in a file called "preferences". I kept the preferences file under my java package.
If i am running the code inside the NetBeans 6.9 IDE it's working file. But once i have created a JAR and try to run the application, it couldn't find the path.
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package mypackage;
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{color:#ff0000}*file:\my jar path\jarname.jar!\mypackage\preferences (The filename, directoryname, or volume label syntax is incorrect)*{color}

Thanks sabre150,
sabre150 wrote:
You cannot update a running jar file. I am sorry. I didn't know about it. Thanks to point out.
There are two ways I approach this depending on my exact requirements -
1) use the java.util.prefs.Preferences APII will try this one
>
2) if not already present I copy the preferences file from the jar to a known place. I use a directory in the user's home directory and normally make the directory name the program with a '.' prefix.
One cannot access files in a jar file using the File API. One needs to use the getResource() or getResourceAsStream() methods on Class or ClassLoader.

How to read, write file inside the JAR file?

Hi all,
I want to read the file inside the jar file, use following method:
File file = new File("filename");
It works if not in JAR file, but it doesn't work if it's in a JAR file.
I found someone had the same problem, but no reply.
http://forum.java.sun.com/thread.jsp?forum=22&thread=180618
Can you help me ? I have tried this for all night !
Thanks in advance
Leo

If you want to read a file from the JAR file that the
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Can Netbeans put a jar file In a jar file?

I just went through the process of getting Eclipse to create a jar file that would execute from a command prompt using a plugin called fatjar :
http://fjep.sourceforge.net/
Details from other thread :http://forum.java.sun.com/thread.jspa?threadID=5219638&tstart=0
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JCommSerial_3_0.jar file that contains all the classes
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http://www.acousticlights.com/netbeans.png
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georgemc wrote:
Why is everyone so obsessed with doing this? The gains are minimal and the problems numerousBecause we are new and don't understand how the java VM actually runs code and the error messages sent by the java machine are cryptic.
My first attempt at using an external jar in a java program lead me to believe that all of the code for a java program would be in a jar file including external jar files, after all the JDK standard library has tons of jars in it so I assumed the external jar file would be linked (as most other programming compiler/linkers I have worked with in my top down programming life).
I find out the answer is so simple that the external jar file could not be found by the VM running my jar file. Like I said, if the VM would have just gave me an error that it could not find a file on a specific directory i never would have perused the idea of jar in a jar (fatjar plugin for Eclipse for example)
Really this is like getting into a race car and not knowing at what RPM to shift gears, sure you can press the pedal and make it go but if you don't understand how it works under the hood you are going to blow the engine if you keep it in first gear.
I have read many posts on these errors, the reason is the error message is just not very descriptive of the original problem. If I try and open a database called xyz.dbf that has one field defined as lastname, in C for example, I would not give the error message "Lastname could not be found) when indeed the lastname could not be found but the reason it could not be found was because the database xyz.dbf could not be found. Further , adding to the error message that the system is looking for xyz.dbf on drive X- subdirectory -mydatabases would complete the error message and allow the user to fix the error. Just what is a non java programmer that is using my java program suppose to do with an Ecception Error in (main) bla bla bla... I know now I need to check for library files myself within my own java programs and give a better error message to the user before the java VM sends out it's cryptic message.
Edited by: metron9 on Sep 25, 2007 11:00 AM

How can I access my java class file in a .jar file ...PLz Help anyone!!

Hi Folks,
I am new in Java programming, have a .jar file that contains .java files that I want no access and use from another .java file. These files in the .jar file basically form a library thus have no main-method. However I can not declare an instance of the library (in the .jar file) and use it within my program.
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temba wrote:
Hi Folks,
I am new in Java programming, have a .jar file that contains .java files that I want no access and use from another .java file. These files in the .jar file basically form a library thus have no main-method. However I can not declare an instance of the library (in the .jar file) and use it within my program. You are making little sense. You can't instantiate .java files.
Plz help ...I have tried all I know in vain.
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Hi, I created a hello.java file, converted into a hello.class file by using the java 2SDk compiler. The problem is that the hello.class file is in a directory I created: C:\JavaBuilder\hello.class
I have a problem converting the hello class file into a jar file. I don't know which approach to take. I've looked at tutorials...but I keep getting more confused each time I view the tutorials on creating jar files. Please can someone help..by taking me through a step by step process. Please be explicit and do not leave or assume that I know any details because I'm a new born beginner. Thank you very much, I seriously appreciate it.

Hi i did as you suggested, only with these exceptions:
jar -cvf hello.jar C:\JavaBuilder\hello.class
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Beginner: Can't convert a hello.class file into a jar file. Please Help!!!

Hi, I created a hello.java file, converted into a hello.class file by using the java 2SDk compiler. The problem is that the hello.class file is in a directory I created: C:\JavaBuilder\hello.class
I have a problem converting the hello class file into a jar file. I don't know which approach to take. I've looked at tutorials...but I keep getting more confused each time I view the tutorials on creating jar files. Please can someone help..by taking me through a step by step process. Please be explicit and do not leave or assume that I know any details because I'm a new born beginner. Thank you very much, I seriously appreciate it.

Hi!
first of all, you should use an upper-case character for the first letter of your classes...
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Updating a properies file in a .jar file

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