A Java app deployed to App Engine fails with a stack trace. Which action should you take?

When a Java app on App Engine fails with a stack trace, especially if it relates to security or class loading, digitally signing all JAR files is a common solution. App Engine's security sandbox can be strict, and unsigned JARs might be treated as untrusted, leading to deployment or runtime errors. Digitally signing them establishes their authenticity and integrity, allowing the App Engine environment to load and execute them securely. Uploading missing JAR files and redeploying is a valid troubleshooting step for missing dependencies, but it doesn't address potential security sandbox issues with existing JARs. Recompiling a specific class with a different hash algorithm is highly specific and unlikely to resolve a general stack trace related to JAR integrity or trust.