YAML Methodology

The YAML data type produced depends on the Java object type being serialized.

• Primitives and primitive objects are converted to YAML scalars.
• Beans and Maps are converted to YAML block mappings.
• Collections and arrays are converted to YAML block sequences.
• Anything else is converted to YAML string scalars (with quoting if necessary).

Data type conversions:

POJO type	YAML type	Example	Serialized form
String	Scalar	serialize("foobar");	foobar
Number	Scalar	serialize(123);	123
Boolean	Scalar	serialize(true);	true
Null	Scalar	serialize(null);	null
Beans with properties of any type on this list	Block mapping	serialize(new MyBean());	p1: val1\np2: true
Maps with values of any type on this list	Block mapping	serialize(new TreeMap());	key1: val1\nkey2: true
Collections and arrays of any type on this list	Block sequence	serialize(new Object[]{1,"foo",true});	- 1\n- foo\n- true

Date/time types (Calendar, Date, Temporal subtypes, Duration) are serialized natively as ISO 8601 strings. Swaps can be used to convert non-serializable POJOs into serializable forms (such as byte[] arrays to Base-64 encoded strings) or to override the default format for types that already have built-in support.

Quoting Rules

YAML strings are quoted when they contain special characters or could be misinterpreted:

• Strings that are YAML reserved words (null, true, false, yes, no, etc.) are double-quoted.
• Strings that look like numbers are double-quoted.
• Strings containing special YAML characters (:, #, {, }, [LINKLABEL_0], etc.) are double-quoted.
• Strings with leading or trailing whitespace are double-quoted.
• Empty strings are double-quoted.
• Strings containing control characters (\n, \t, \b, etc.) are double-quoted with proper escape sequences.

Nested Structures

YAML uses indentation to represent nested structures. Each level of nesting increases the indent by 2 spaces:

person:
  name: John Smith
  addresses:
    - street: 100 Main Street
      city: Anywhereville
      state: NY
    - street: 200 Oak Avenue
      city: Sometown
      state: CA

Empty maps and collections are serialized using flow-style notation ({} and [] respectively).