Question

I’m trying to fetch list of files using a method that apparently works well with non-applet Java code.

I’m fully aware it’s messy; I’m just trying to get this to work for a school assignment. (I’m no fan of Java.)

        CodeSource src = MemoryButtonHelper.class.getProtectionDomain().getCodeSource();
        if (src == null) {
            throw new Exception();
        }

        URL jar = src.getLocation();
        System.out.println("Loading from " + jar);

        JarFile zf=new JarFile(jar.toString()); //jar.openStream());

        final Enumeration<JarEntry> entries = zf.entries();

        while (entries.hasMoreElements()) {
            final JarEntry ze = entries.nextElement();

            if(ze.getName().endsWith(".jpg") || ze.getName().endsWith(".png"))
            {
                System.out.println("Adding " + ze.getName());
                slikeList.add(ze.getName());
            }
        }
        zf.close();

Unfortunately, I’m getting a security exception.

java.security.AccessControlException: access denied (java.lang.RuntimePermission getProtectionDomain)
    at java.security.AccessControlContext.checkPermission(AccessControlContext.java:374)
    at java.security.AccessController.checkPermission(AccessController.java:546)
    at java.lang.SecurityManager.checkPermission(SecurityManager.java:532)
    at java.lang.Class.getProtectionDomain(Class.java:2106)
    at hr.tvz.programiranje.java.deseti.helpers.MemoryButtonHelper.getSlike(MemoryButtonHelper.java:75)
        … ad nauseam … 

According to Java Console, exception appears to occur before the println("Loading from " + jar).

This is a bonus point assignment which specifically says that we must fetch the list of images from the JAR file. Since this is my first encounter with the applets, I’m not sure what I can do to fetch the list of images.

Answer 1

..we must fetch the list of images from the JAR file.

Who put them in there in the first place? If the answer is ‘we did’, the solution is simple.

• Include a list of image path/names at a known location (e.g. images/imagelist.txt) in the Jar.
• Obtain a reference to the list using getResource(String).
• Read the list (probably using a line reader).

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Apparently they want me to list the contents of the jar as-is, without extra metadata.

OK. If you can form an URL to (and thereby an InputStream from) the Zip file, it is possible to establish a ZipInputStream from it. This should work whether the URL is to a Zip/Jar cached on the local file-system or still at the server.

1. Get an URL to the Jar.
2. Establish a ZipInputStream from the URL.
3. Iterate the entries using getNextEntry() until null
4. Examine each one for a potential match and if it does, add it to an ArrayList.

Of course, you’ll still need signed & trusted code to call for the protection domain.

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Images are definitely in the same JAR

To get an URL to the Jar, try this (untested). Let’s assume the applet is com.our.BookingApplet.

1. Obtain an URL to the Jar in which the class resides, using
   
   URL urlToApplet = this.getClass().getResource("/com/our/BookingApplet.class")
2. String[] parts = urlToApplet.toString().split("!") will provide two parts, the first will be a String representation of the Jar URL.
3. Use that String to establish an URL, then use the URL as described in the previous update.