public enum Include

{

/**

* Value that indicates that property is to be always included,

* independent of value of the property.

* 包含所有属性，默认为ALWAYS

*/

ALWAYS,

/**

* Value that indicates that only properties with non-null

* values are to be included.

* 包含不为NUll的属性

*/

NON_NULL,

/**

* Value that indicates that properties are included unless their value

* is:

*

*

null

*

"absent" value of a referential type (like Java 8 `Optional`, or

* {link java.utl.concurrent.atomic.AtomicReference}); that is, something

* that would not deference to a non-null value.

*

* This option is mostly used to work with "Optional"s (Java 8, Guava).

*

* @since 2.6

*/

NON_ABSENT,

/**

* Value that indicates that only properties with null value,

* or what is considered empty, are not to be included.

* Definition of emptiness is data type specific; see below

* for details on actual handling.

*

* Default emptiness for all types includes:

*

*

Null values.

*

"Absent" values (see {@link #NON_ABSENT})

*

* so that as baseline, "empty" set includes values that would be

* excluded by both {@link #NON_NULL} and {@link #NON_ABSENT}.

*

* Beyond this base, following types have additional empty values:

*

*

For {@link java.util.Collection}s and {@link java.util.Map}s,

* method isEmpty() is called;

*

*

For Java arrays, empty arrays are ones with length of 0

*

*

For Java {@link java.lang.String}s, length() is called,

* and return value of 0 indicates empty String

*

*

* and for other types, null values are excluded but other exclusions (if any).

*

* Note that this default handling can be overridden by custom

* JsonSerializer implementation: if method isEmpty()

* is overridden, it will be called to see if non-null values are

* considered empty (null is always considered empty).

*

* Compatibility note: Jackson 2.6 included a wider range of "empty" values than

* either earlier (up to 2.5) or later (2.7 and beyond) types; specifically:

*

*

Default values of primitive types (like 0 for `int`/`java.lang.Integer`

* and `false` for `bool`/`Boolean`)

*

*

Timestamp 0 for date/time types

*

*

* With 2.7, definition has been tightened back to only containing types explained

* above (null, absent, empty String, empty containers), and now

* extended definition may be specified using {@link #NON_DEFAULT}.

*/

NON_EMPTY,

/**

* Meaning of this setting depends on context: whether annotation is

* specified for POJO type (class), or not. In latter case annotation

* is either used as the global default, or as property override.

*

* When used for a POJO, definition is that only values that differ from

* the default values of POJO properties are included. This is done

* by creating an instance of POJO using zero-argument constructor,

* and accessing property values: value is used as the default value

* by using equals() method, except for the case where property

* has `null` value in which straight null check is used.

*

* When NOT used for a POJO (that is, as a global default, or as property

* override), definition is such that:

*

*

All values considered "empty" (as per {@link #NON_EMPTY}) are excluded

*

Primitive/wrapper default values are excluded

*

Date/time values that have timestamp (`long` value of milliseconds since

* epoch, see {@link java.util.Date}) of `0L` are excluded

*

*/

NON_DEFAULT,

/**

* Pseudo-value used to indicate that the higher-level defaults make

* sense, to avoid overriding inclusion value. For example, if returned

* for a property this would use defaults for the class that contains

* property, if any defined; and if none defined for that, then

* global serialization inclusion details.

*

* @since 2.6

*/

USE_DEFAULTS

;

}