karatelabs/karate · error · RuntimeException

Failed to create resource from URL

Error message

Failed to create resource from URL: {url}

What it means

Thrown from the fallback branch of the URL resource factory: when a jar: URL cannot be mounted through the JAR filesystem provider, the code streams the entry content into a MemoryResource instead; if even that openStream/read fails, this error is thrown naming the URL.

Solutions

  1. Verify the jar file exists and the entry path is correct: 'unzip -l app.jar' and compare the entry path exactly (case-sensitive)
  2. Inspect the cause chain (ex) to see whether the entry is missing vs a read failure
  3. Rebuild/redeploy the jar so it actually contains the resource
  4. If running under jpackage, add the zip filesystem module or ship the resource outside the jar and reference it by file path

Example fix

// before
Resource r = Resource.fromUrl(new URL("jar:file:/app/lib/rules.jar!/rules/discount.js"));
// after
try {
    Resource r = Resource.fromUrl(new URL(jarUrl));
} catch (RuntimeException e) {
    // fallback: unpack once at startup and use a file resource
    Resource r = Resource.fromFilePath("/app/exploded/rules/discount.js");
}
Defensive patterns

Strategy: try-catch

Validate before calling

// verify the jar entry exists before loading
java.util.zip.ZipFile zip = new java.util.zip.ZipFile("/app/lib/rules.jar");
if (zip.getEntry("rules/discount.js") == null) {
    throw new IllegalStateException("entry missing from jar");
}

Try / catch

try {
    Resource r = Resource.fromUrl(jarUrl);
} catch (RuntimeException e) {
    // cause chain: streaming failure inside the zipfs fallback
    throw new IllegalStateException("jar resource unusable: " + jarUrl, e.getCause());
}

Prevention

When it happens

Trigger: Loading a resource from inside a jar/zip URL where the JAR filesystem provider is unavailable (e.g. jpackage/JavaFX packaged apps) AND url.openStream() or reading the content also throws — typically the jar entry does not exist or the jar file is unreadable/corrupt.

Common situations: jpackage-packaged desktop apps where the NIO zipfs provider is missing; the referenced jar was moved, deleted, or rebuilt; the entry path inside the jar has wrong casing; shaded jars missing the resource.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/8027a2c65f34c66b. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/common/Resource.java:869

                byte[] bytes = FileUtils.toBytes(is);
                return root != null ? new UrlResource(url, bytes, root) : new UrlResource(url, bytes);
            } catch (Exception e) {
                throw new RuntimeException("Failed to fetch content from URL: " + url, e);
            }
        }

        // Handle file:// and jar:// URLs
        try {
            Path path = urlToPath(url, root);
            return root != null ? new PathResource(path, root) : new PathResource(path);
        } catch (java.nio.file.ProviderNotFoundException e) {
            // JAR file system provider not available (common in jpackage/JavaFX apps)
            // Fall back to streaming the resource content
            try (java.io.InputStream is = url.openStream()) {
                String content = FileUtils.toString(is);
                return root != null ? new MemoryResource(content, root) : new MemoryResource(content);
            } catch (Exception ex) {
                throw new RuntimeException("Failed to create resource from URL: " + url, ex);
            }
        } catch (Exception e) {
            throw new RuntimeException("Failed to create resource from URL: " + url, e);
        }
    }

}

View on GitHub (pinned to a22eb90246)