An OkHttp DNS implementation that validates resolved IP addresses against an SSRF policy, rejecting non-public addresses and closing the DNS rebinding window. This is a self-contained security component that can be extracted and reused in any OkHttp-based HTTP client to prevent server-side request forgery attacks. It demonstrates non-obvious security engineering by addressing the DNS rebinding race condition.

A zip input stream wrapper that prevents zip-slip directory traversal attacks by verifying that each extracted entry's canonical path is within the target output directory. This is a reusable security utility that can be applied to any Java zip extraction code to mitigate path traversal vulnerabilities. It is self-contained and demonstrates defensive file-handling practices.

A custom AbstractList implementation that automatically stamps each added element with the owning object's model context, ensuring consistent parent references in a hierarchical data model. This pattern is reusable for any tree-structured object model where child elements need to maintain a back-reference to their parent. It is self-contained and demonstrates a clean solution to a common object-modeling problem.

A generic utility that merges two lists positionally or via an IMatcher interface, producing left/right MergeNode results. This is a reusable data structure for implementing diff/merge operations on ordered collections. It is self-contained, generic, and can be extracted into any Java project needing list comparison or merging functionality.