gson

Gson is a Java library from Google that solves a very common programming problem: converting Java objects into JSON format and back again. JSON (JavaScript Object Notation) is a lightweight text format used to send data between apps, store configuration, or communicate with web services. Without a library like Gson, developers would have to manually write code to translate each field of their data objects into JSON text — tedious and error-prone work.

Gson handles this automatically. You call a simple method like toJson() on any Java object and get a JSON string back. Call fromJson() with a JSON string and a target class, and Gson reconstructs the Java object for you. What makes it stand out from similar libraries is that it works on classes you don't own or can't modify — you don't need to add special annotations to your code. It also handles complex generic types (like a list of lists of custom objects), which many competitors handle poorly.

You would use Gson when building a Java application that needs to talk to a web API, save data in a portable format, or pass structured information between different parts of a system. It is especially common in server-side Java applications and older Android apps, though the README advises against using it on Android today due to compatibility issues with code optimization tools that Android apps typically run.

The library is written in Java, requires Java 8 or newer, and is available via the Maven Central repository. It is currently in maintenance mode, meaning bugs get fixed but no major new features are planned.