Question

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Loading resource bundles using a custom class loader

I’ve made a custom class loader which downloads a jar from my website, and then runs it.
The problem is: my (downloaded) jar needs some resources such as png images, etc…

If I run my (downloaded) jar directly at a command prompt, it works. The resources are loaded like that:

getClass().getResource("/images/logo.png")

Now, if I run it with my custom class loader, using:

Class<?> c = classLoader.loadClass("MainClass");
c.getMethod("main", new Class[] { java.lang.String[].class}).invoke(null, new Object[]{new String[] {"arg1_goes_here"}});

I get a null exception because it can’t load the resource.

When I load my jar file into memory, I do something like that:

String name = entry.getName();
if(name.endsWith(".class")) {
    name = name.substring(0, name.length() - 6).replace('/', '.');
    classbytes = getResourceData(input);
    classes.put(name, classbytes);
} else {
    classbytes = getResourceData(input);
    if (name.charAt(0) != '/') {
        name = "/" + name;
    }
    resources.put(name, classbytes);
}

I’m loading my class using:

defineClass(classToLoad, buffer, 0, buffer.length, null);

where buffer is the byte array containing the code.

So my question is the following: Is there a kind of defineResource() in Java?

Thanks.

Answer 1

Problem solved,

I’ve written my own method public InputStream getResourceAsStream(String name).

Here is the code:

public InputStream getResourceAsStream(String name)
{
    byte[] buffer = resources.get(name);
    return new ByteArrayInputStream(buffer);
}

resourcesis a Map that contains my resource data.

Then, in my code, I can use the inputstream to get back my resource. Easy and safe.