How do I parse a JSON File?

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Serde is the preferred JSON serialization provider. You can read the JSON text from a file a number of ways. Once you have it as a string, use serde_json::from_str:

fn main() {
    let the_file = r#"{
        "FirstName": "John",
        "LastName": "Doe",
        "Age": 43,
        "Address": {
            "Street": "Downing Street 10",
            "City": "London",
            "Country": "Great Britain"
        },
        "PhoneNumbers": [
            "+44 1234567",
            "+44 2345678"
        ]
    }"#;

    let json: serde_json::Value =
        serde_json::from_str(the_file).expect("JSON was not well-formatted");
}

Cargo.toml:

[dependencies]
serde = { version = "1.0.104", features = ["derive"] }
serde_json = "1.0.48"

You could even use something like serde_json::from_reader to read directly from an opened File.

Serde can be used for formats other than JSON and it can serialize and deserialize to a custom struct instead of an arbitrary collection:

use serde::Deserialize;

#[derive(Debug, Deserialize)]
#[serde(rename_all = "PascalCase")]
struct Person {
    first_name: String,
    last_name: String,
    age: u8,
    address: Address,
    phone_numbers: Vec<String>,
}

#[derive(Debug, Deserialize)]
#[serde(rename_all = "PascalCase")]
struct Address {
    street: String,
    city: String,
    country: String,
}

fn main() {
    let the_file = /* ... */;

    let person: Person = serde_json::from_str(the_file).expect("JSON was not well-formatted");
    println!("{:?}", person)
}

Check the Serde website for more details.

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