Read JSON file using from_reader

---

examples/json/json-read-from-reader/data.json

{"x":1,"y":2, "text":"Hello World!"}

examples/json/json-read-from-reader/Cargo.toml

[package]
name = "json-read-from-reader"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0.97"

examples/json/json-read-from-reader/src/main.rs

use std::fs::File;
//use std::io::Read;

use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct Point {
    x: i32,
    y: i32,
    text: String,
}

fn main() {
    read_any_json();
    read_struct_json();
}

fn read_any_json() {
    let filename = "data.json";
    match File::open(filename) {
        Ok(file) => {
            let data: serde_json::Value = serde_json::from_reader(file).expect("JSON parsing error");
            dbg!(&data);

            let text = match data.get("text") {
                Some(val) => val.as_str().unwrap(),
                None => panic!("Field text does not exist"),
            };
            println!("{}", text);

            let x = match data.get("x") {
                Some(val) => val.as_i64().unwrap(),
                None => panic!("Field x does not exist"),
            };
            let y = match data.get("y") {
                Some(val) => val.as_i64().unwrap(),
                None => panic!("Field y does not exist"),
            };
            println!("{}", x+y);
        },
        Err(error) => {
            println!("Error opening file {}: {}", filename, error);
        },
    }
}


fn read_struct_json() {
    let filename = "data.json";
    match File::open(filename) {
        Ok(file) => {
            let data: Point = serde_json::from_reader(file).unwrap();
            println!("data = {:?}", data);
            println!("{}", data.x + data.y);
            println!("{}", data.text);
        }
        Err(error) => {
            println!("Error opening file {}: {}", filename, error);
        },
    }
}

Hello World!
3
data = Point { x: 1, y: 2, text: "Hello World!" }
3
Hello World!