ClientBundle

ClientBundle is a resource bundling pattern and API most commonly associated with Google Web Toolkit (GWT). It defines an interface-based mechanism for declaring application resources — such as images, CSS, text, and binary data — so the toolkit can combine and optimize them at compile time into a compact, efficient representation used by the client application.

A ClientBundle interface declares methods that return resource types (for example ImageResource, CssResource, TextResource, DataResource). Implementations are generated by the GWT compiler and accessed through deferred binding (typically via GWT.create). Annotations such as @Source specify the file to associate with each resource method. CssResource supports obfuscation and renaming of CSS class names to avoid collisions and reduce size. ImageResource can produce CSS sprites to minimize HTTP requests.

Advantages include fewer HTTP requests, smaller overall payloads after compression, compile-time validation of resource references, and automatic renaming or optimization of CSS and images. Limitations include reduced flexibility for runtime resource changes, potentially larger JavaScript output if many resources are inlined, and the need to rebuild the application to update bundled assets. ClientBundle is primarily a compile-time optimization; similar bundling concepts exist in other web-build systems and module bundlers.