How do I parse a JSON File?

Question

I have this so far in my goal to Parse this JSON data in Rust:

extern crate rustc_serialize; use rustc_serialize::json::Json; use std::fs::File; use std::io::copy; use std::io::stdout;  fn main() {     let mut file = File::open("text.json").unwrap();     let mut stdout = stdout();     let mut str = &copy(&mut file, &mut stdout).unwrap().to_string();     let data = Json::from_str(str).unwrap(); } 

and text.json is

{     "FirstName": "John",     "LastName": "Doe",     "Age": 43,     "Address": {         "Street": "Downing Street 10",         "City": "London",         "Country": "Great Britain"     },     "PhoneNumbers": [         "+44 1234567",         "+44 2345678"     ] } 

What should be my next step into parsing it? My primary goal is to get JSON data like this, and parse a key from it, like Age.

Answer 1

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.

Answer 2

Solved by the many helpful members of the Rust community:

extern crate rustc_serialize; use rustc_serialize::json::Json; use std::fs::File; use std::io::Read;  fn main() {     let mut file = File::open("text.json").unwrap();     let mut data = String::new();     file.read_to_string(&mut data).unwrap();      let json = Json::from_str(&data).unwrap();     println!("{}", json.find_path(&["Address", "Street"]).unwrap()); }