Generate pretty (indented) JSON with serde

Question

Using the serde_json crate, I can use

::serde_json::to_string(&obj)

to serialize an object into a JSON string. The resulting JSON uses compact formatting, like:

{"foo":1,"bar":2}

But how do I generate pretty/indented JSON? For example, I'd like to get this:

{
  "foo": 1,
  "bar": 2
}

dtolnay · Accepted Answer · 2023-03-08T05:48:59.860

The serde_json::to_string_pretty function generates pretty-printed indented JSON.

use serde_json::json;

fn main() {
    let obj = json!({"foo":1,"bar":2});
    println!("{}", serde_json::to_string_pretty(&obj).unwrap());
}

This approach defaults to 2 spaces of indentation, which happens to be what you asked for in your question. You can customize the indentation by using PrettyFormatter::with_indent.

use serde::Serialize;
use serde_json::json;

fn main() {
    let obj = json!({"foo":1,"bar":2});

    let mut buf = Vec::new();
    let formatter = serde_json::ser::PrettyFormatter::with_indent(b"    ");
    let mut ser = serde_json::Serializer::with_formatter(&mut buf, formatter);
    obj.serialize(&mut ser).unwrap();
    println!("{}", String::from_utf8(buf).unwrap());
}

I feel like `formatter::to_string(&obj)` and `formatter::to_writer(w, &obj)` are a missing piece of the API. — BallpointBen, Mar 08 '23 at 04:15

score 26 · Answer 2 · answered Mar 10 '17 at 15:34

26

Use the to_string_pretty function to get indented JSON:

::serde_json::to_string_pretty(&obj)

answered Mar 10 '17 at 15:34

Jo Liss

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Is there any way to set indentation? By default it seems 2 spaces. – pietrovismara Aug 26 '17 at 13:53

Generate pretty (indented) JSON with serde

2 Answers2

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