Accessing a resource within a .jar

Posted by Emanuele Gesuato Mon, 06 Feb 2006 01:08:00 GMT

Sometimes it is useful to distribute an application in a jar file through Java Web Start or any other way. So, you could have to read some resource (images or properties file) from inside a jar. How can you do it ? It’s very simple, here’s an example to retrieve an image:

ImageIcon image = (new ImageIcon(getClass().getResource("yourpackage/mypackage/image.gif")));

In general, you can retrieve an InputStream in the following way:

InputStream is = this.getClass().getClassLoader()    .getResourceAsStream("yourpackage/mypackage/myfile.xml");

It will run inside or outside the jar. Enjoy !

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  1. Avatar Lucio Benfante said about 13 hours later:

    ...or briefly:

    InputStream is = 
    this.getClass()
    .getResourceAsStream(
        "yourpackage/mypackage/myfile.xml");
  2. Avatar my jug said about 17 hours later:

    I think , it’s not complete demonstrative. Where is the code, and the ”.jar” into code or in your explanation??

  3. Avatar Dario Santamaria said about 22 hours later:

    The ”.jar” into code or in your explanation must be in your classpath. So no name of the ”.jar” is required inside the code. You can include your jar in your classpath using:

    java -cp .:<myjarfile>.jar myapplication
  4. Avatar my jug said 6 days later:

    boh , I can’t understand , however It’s not so important!

    Mah , maybe simply ,with that code you can read a file into jar file.

    but ….

    What’s means distribuite an application ?? Where is RMI ?? What’s Java Web Start ??

  5. Avatar Lucio Benfante said 8 days later:

    No, with that code you can read a “file” from everywhere, without worrying about the real path or the storage of the “file” (resource), that can even be in a jar or elsewhere in the net, or in a database. It delegates the loading to the classloader, so using the same machanism used for loading the classes in the JVM.

    “my jug”, about the other questions…are them on topic? I think you are just trolling. If you are really interested, we have also a mailing-list…but…no stupid questions, please.

  6. Avatar my jug said 8 days later:

    Sorry fante,

    I’m not a trolling , simply I don’t understand your sentence “Sometimes it is useful to distribute an application in a jar file through Java Web Start or any other way” and the explanation with your code.

    .. but it’s not important , it’s only curiosity …

    Yes, of sure, the next time I don’t back in jugpadova.it

  7. Avatar Lucio Benfante said 9 days later:

    “my jug”, it’s not my sentence: Emanuele wrote the original post.

    What is not clear or unusual in distributing a Java application in a Jar or through the Java Web Start?

    Some links:

    http://java.sun.com/products/javawebstart/
    http://mindprod.com/jgloss/javawebstart.html

  8. Avatar Rui Pereira said 611 days later:

    Hi there. This all sounds super cool, but I can’t get it work.

    I got a JAR file with a default class with a main method to be called.

    so the inside of the JAR looks like so :

    com/me/stuff/Bling.class images/image.gif META-INF/MANIFEST.MF

    All works except for the image bit !

    in my Bling class I got :

    java.net.URL imgURL = getClass().getResource(“images/image.gif”); image = Toolkit.getDefaultToolkit().getImage(imgURL);

    the exception I get when I run my dudle.jar file ( java -jar dudle.jar ) is :

    Uncaught error fetching image: java.lang.NullPointerException at sun.awt.image.URLImageSource.getConnection(URLImageSource.java:97) at sun.awt.image.URLImageSource.getDecoder(URLImageSource.java:107) at sun.awt.image.InputStreamImageSource.doFetch(InputStreamImageSource.java:240) at sun.awt.image.ImageFetcher.fetchloop(ImageFetcher.java:172) at sun.awt.image.ImageFetcher.run(ImageFetcher.java:136)

    any thoughs ? Thx Rp

  9. Avatar Lucio Benfante said 616 days later:

    I tried the following code, and it works:

    package provaimage;

import java.awt.Image;
import java.awt.Toolkit;
import java.net.URL;

public class Main {

    public static void main(String[] args) {
        URL imgURL = Main.class.getResource("images/image.gif");
        Image image = Toolkit.getDefaultToolkit().getImage(imgURL);
        System.out.println(image);
    }
}

    Check that imgURL is not null. I think it could be a classloading problem. Try also with the “long” form:

    getClass().getClassLoader().getResource(...

  10. Avatar pant.uday@gmail.com said 880 days later:

    Thanks for the help. Had been looking for this.

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  13. Avatar Web Design London said 1536 days later:

    Hi Emanuele…!!!!!!

    I think the given idea by you is very interesting… This all sounds super cool because this is the thing for which I was been looking… Thanks for me such an useful information.. great stuff..!!! Keep the good work.. Hope to see your more and more post so on.

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    To perform basic tasks with JAR files, we can use the Java Archive Tool Because the Java Archive tool is invoked by using the jar command, for convenience we’ll call it the “Jar tool”.

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    Look here!

    ImageIcon icon = new ImageIcon(ClassLoader.getSystemResource(“/.png”));

    URl url = ClassLoader.getSystemResource(String sourceTarget);

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    I used that code with the “long form” (maybe not necessary for it to work) and without any path to the image, because after looking into the generated jar, the file was in the root location, not under its physically containing folder. This was the reason it was failing for me and imgURL did not have any value.

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