Package org.apache.juneau.marshall.toml

Class TomlSerializer

java.lang.Object
org.apache.juneau.marshall.Context
org.apache.juneau.marshall.MarshallingContextable
org.apache.juneau.marshall.MarshallingTraverseContext
org.apache.juneau.marshall.serializer.Serializer
org.apache.juneau.marshall.serializer.WriterSerializer
org.apache.juneau.marshall.toml.TomlSerializer
All Implemented Interfaces:
Function<Object,String>, ThrowingFunction<Object,String>, RecordWritable, TomlMetaProvider
public class TomlSerializer extends WriterSerializer implements TomlMetaProvider, RecordWritable
Serializes POJOs to TOML v1.0.0 format.

TOML (Tom's Obvious Minimal Language) maps unambiguously to hash tables with native typing. See TOML v1.0.0 specification.

Media types

Produces: application/toml
Accepts: application/toml

Bean-to-TOML mapping
  • Simple properties → key-value pairs
  • Nested beans → [tableName] sections
  • Collections of beans → [[tableName]] array of tables
  • Collections of simple values → key = [a, b, c]
  • Maps with string keys → [mapName] table
  • Null properties are omitted (TOML has no null type)
Example:

// Serialize a bean to TOML String toml = TomlSerializer.DEFAULT.write(myBean); // Serialize a map (e.g. config with nested sections) Map<String, Object> config = Map.of("name", "myapp", "port", 8080); toml = TomlSerializer.DEFAULT.write(config); // Use the marshaller for convenience toml = Toml.of(config); // Custom serializer with whitespace for readability TomlSerializer s = TomlSerializer.create().ws().build(); toml = s.write(config);

Example output (Map of name/age):

name = "Alice" age = 30

Complex (nested table + array):

name = "Alice" age = 30 tags = ["a", "b", "c"] [address] street = "123 Main St" city = "Boston" state = "MA"

Limitations compared to JSON

TOML is a configuration format with a more restricted type system than JSON. The following features supported by JsonSerializer are not available or limited in TOML:

  • Null values — TOML has no null type. By default, null properties are omitted. Use keepNullProperties() to write the configured nullValue string (e.g. <NULL>) instead.
  • Map keys — TOML tables only support string keys. Maps with non-string keys (e.g. Map<Integer,String>) have keys converted via toString(); ensure results are valid TOML keys. Null keys are serialized as the string null.
  • Polymorphic types — addBeanTypes() and addRootType() add _type discriminators for polymorphic parsing; use with care as TOML structure differs from JSON.
  • Root-level collections — TOML expects a root table. Root arrays use array-of-tables ([[item]]) for beans/maps, or a _value wrapper for primitives and simple arrays.
  • Duplicate keys — TOML forbids duplicate keys; structures that would produce duplicate keys may yield invalid TOML.
Notes:
  • This class is thread safe and reusable.