这是rust解析json数据的一个简单示例。现在解析后，我如何找到一个serde_json::Value的键，例如："name", "age", "phones"在这个例子中？

fn json_hello_world() {
    // Some JSON input data as a &str. Maybe this comes from the user.
    let data = r#"
        {
            "name": "John Doe",
            "age": 43,
            "phones": [
                "+44 1234567",
                "+44 2345678"
            ]
        }"#;

    // Parse the string of data into serde_json::Value.
    let value: serde_json::Value = serde_json::from_str(data).unwrap();

    println!(
        "Please call {} at the number {}",
        value["name"], value["phones"][0]
    );

    /*
    // how do I print out the keys?
    for key in value.keys() {
        println!("{}", key);
    }
    */
}

fn main() {
    json_hello_world();
}