How to Stream and Parse Large JSON Files in Rust

Use the serde_json crate with serde_json::Deserializer::from_reader to parse large JSON files incrementally without loading them into memory.

use std::fs::File;
use serde_json::Deserializer;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let file = File::open("large.json")?;
    let mut deserializer = Deserializer::from_reader(file);
    
    while let Some(value) = serde_json::Value::deserialize(&mut deserializer)? {
        println!("Parsed: {value}");
    }
    Ok(())
}

Add serde_json = "1" and serde = { version = "1", features = ["derive"] } to your Cargo.toml.

Streaming and parsing large JSON files in Rust reads a massive file piece by piece instead of trying to fit the whole thing into your computer's memory at once. It works like reading a book one page at a time rather than photocopying the entire library before starting. You use this when your JSON data is too big to fit in RAM or when you need to process data as it arrives.