JSON Serializers

The JsonSerializer class serializes POJOs (beans, collections, maps and simple values) into JSON text.

When to use it

Use JsonSerializer when you need strict JSON output, for example a REST response or a file another tool reads. For a one-line conversion with the default settings, the Json marshaller (Json.of(pojo)) is shorter; see Marshallers. For JSON5 output (unquoted keys, single quotes), use Json5Serializer instead; see JSON 5.

Example

import org.apache.juneau.marshall.json.*;

public class JsonSerializerExample {

    public static class Person {
        public String name = "John Smith";
        public int age = 45;
        public String nickname;
    }

    public static void main(String[] args) throws Exception {
        // Compact output with the default serializer: {"age":45,"name":"John Smith"}
        String compact = JsonSerializer.DEFAULT.write(new Person());

        // A serializer with whitespace that also writes null properties.
        JsonSerializer serializer = JsonSerializer.create().ws().keepNullProperties().build();
        String readable = serializer.write(new Person());
        System.out.println(readable);
    }
}

The second serializer prints:

{
	"age": 45,
	"name": "John Smith",
	"nickname": null
}

Serializers are immutable and thread-safe, so build one once and reuse it.

Options

The pre-configured instances cover the common cases:

Instance	Output
`JsonSerializer.DEFAULT`	Compact JSON.
`JsonSerializer.DEFAULT_READABLE`	JSON with whitespace and indentation.

For anything else, start from JsonSerializer.create(). The builder settings readers reach for first (all off by default):

Builder method	Effect
`ws()`	Add whitespace and indentation (same as `useWhitespace()`).
`sq()`	Use single quotes instead of double quotes.
`keepNullProperties()`	Write bean properties whose value is `null`.
`trimEmptyCollections()` / `trimEmptyMaps()`	Omit empty collections and maps.
`sortCollections()` / `sortMaps()`	Sort collection entries and map keys.
`addBeanTypes()`	Add `_type` properties so a parser can rebuild the original classes.