Is FastJson Really Faster? Performance, Popularity, and Why You Might Drop It

Why FastJson?

FastJson is Alibaba's open‑source JSON parsing library that can parse JSON strings, serialize Java beans to JSON, and deserialize JSON back to Java objects. It is popular among Java developers, with speed marketed as its main advantage.

Is It Really Fast?

Without prior research, a simple benchmark was performed comparing FastJson with the widely used Jackson and Google’s Gson. The test ran on JDK 8, an AMD 3700X CPU, and 3200 MHz RAM, converting simple and complex objects to and from strings ten million times. The results (shown in the image) indicate FastJson is about 20% faster than Jackson, while Gson is the slowest.

Although FastJson appears fastest, the test did not cover memory usage or large‑document handling. In modern applications even the slower Gson meets performance needs, and factors like I/O optimization and parallel processing are often more impactful than raw parsing speed.

FastJson Is Not That Popular

FastJson’s Maven Central usage is far lower than that of Jackson and Gson, placing it in a different magnitude of adoption. Discussions on platforms like Zhihu suggest FastJson suffers from lower code quality, with many unresolved issues (over 1,200 reported). Screenshots show numerous open issues and problematic source code, including serious logic errors in date‑format handling that cause incorrect conversions.

Dropping FastJson

In the author’s projects, Spring Boot already uses Jackson for JSON processing to keep dependencies minimal. Some team members still use Gson or FastJson without strict guidelines. Given Jackson’s strong ecosystem and the drawbacks of FastJson, the recommendation is to standardize on Jackson and gradually phase out FastJson.