explaingit

alibaba/fastjson

★ 25,660JavaAudience · developerComplexity · 2/5StaleLicenseSetup · easy

TLDR

Fast Java library for converting objects to and from JSON, the standard format for web APIs and data storage.

Mindmap

mindmap
  root((repo))
    What it does
      Convert objects to JSON
      Parse JSON to objects
      Handle complex types
    Key features
      High performance
      Works with any object
      Simple API
    Use cases
      Backend services
      Android apps
      API integrations
    Tech stack
      Java
      Maven
      Gradle
    Audience
      Java developers
      Backend engineers

Things people build with this

USE CASE 1

Serialize Java objects to JSON for sending data over web APIs.

USE CASE 2

Parse JSON responses from external services back into Java objects.

USE CASE 3

Store and retrieve structured data in JSON format from databases.

USE CASE 4

Build Android apps that communicate with backend services using JSON.

Tech stack

JavaMavenGradle

Getting it running

Difficulty · easy Time to first run · 5min
Use freely for any purpose including commercial. Keep the notice and disclose changes to the patent grant.

In plain English

Fastjson is a Java library from Alibaba that converts Java objects into JSON (a standard text format for representing data) and back again. JSON is the format most web APIs use to send and receive data, so a library like this is a core building block for any Java application that talks to other services or stores structured data. The key selling point is speed: Fastjson was designed to be among the fastest JSON parsers available for Java. It provides simple methods, essentially toJSONString() to turn an object into JSON text, and parseObject() to turn JSON text back into a Java object. It works with any Java object, including ones you cannot modify, and handles complex types like generics (Java's system for writing reusable code that works with different data types). You would use Fastjson in a Java backend service or Android app whenever you need to serialize (convert to JSON) or deserialize (parse from JSON) data efficiently. It is available via Maven and Gradle, the standard Java dependency management tools. The readme notes that Fastjson 2.0.x has been released as a faster and more secure successor, and existing users are encouraged to upgrade to that newer version.

Copy-paste prompts

Prompt 1
Show me how to use Fastjson to convert a Java object to JSON string and back.
Prompt 2
How do I integrate Fastjson into my Maven project to handle JSON serialization?
Prompt 3
Write example code using Fastjson's toJSONString() and parseObject() methods.
Prompt 4
How does Fastjson handle complex Java types like generics and custom objects?
Prompt 5
What's the difference between Fastjson 1.x and 2.0.x, and should I upgrade?
Open on GitHub → Explain another repo

Generated 2026-05-18 · Model: sonnet-4-6 · Verify against the repo before relying on details.