Supported Java Types

When persisting a class, a persistence solution needs to know how to persist the types of each field in the class. Clearly a persistence solution can only support a finite number of Java types. It cannot know how to persist every possible type creatable. The JDO specifications define lists of types that are required to be supported by all implementations of those specifications. This support can be conveniently split into two parts

  • An object that can be referred-to (object reference, providing a relation) and that has an "identity" - First Class Object (FCO). JDO requires an implementation to support PersistenceCapable types, as well as object/interface fields that refer to PersistenceCapable objects.

  • An object that does not have an "identity" - Second Class Object (SCO). This is something like a String or Date field in a class. It can also be a Collection, that contains other objects.


First-Class (FCO) Types

JDO requires objects that are PersistenceCapable to be FCO. In addition it supports persisting fields of Interface or java.lang.Object type as FCO (since these are just references to PersistenceCapable objects).


Second-Class (SCO) Types

The table below shows the supported SCO java types in JDO2. The table also shows the default-fetch-group (DFG) setting for that Java type (so whether it is retrieved by default when retrieving an object with a field of that type), whether the field is persisted by default (if it is "false" then you would have to add persistence-modifier="persistent" to the field for it to be persisted by JDO), and whether the java type can be used as part of the primary key.

Java Type DFG? Persistent? PK?

boolean

byte

char

double

float

int

long

short

boolean[]

byte[]

char[]

double[]

float[]

int[]

long[]

short[]

java.lang.Boolean

java.lang.Byte

java.lang.Character

java.lang.Double

java.lang.Float

java.lang.Integer

java.lang.Long

java.lang.Short

java.lang.Boolean[]

java.lang.Byte[]

java.lang.Character[]

java.lang.Double[]

java.lang.Float[]

java.lang.Integer[]

java.lang.Long[]

java.lang.Short[]

java.lang.Number

java.lang.Object

java.lang.String

java.lang.String[]

java.math.BigDecimal

java.math.BigInteger

java.math.BigDecimal[]

java.math.BigInteger[]

java.sql.Date

java.sql.Time

java.sql.Timestamp

java.util.ArrayList

java.util.Collection

java.util.Currency

java.util.Date

java.util.Date[]

java.util.HashMap

java.util.HashSet

java.util.Hashtable

java.util.LinkedHashMap

java.util.LinkedHashSet

java.util.LinkedList

java.util.List

java.util.Locale

java.util.Locale[]

java.util.Map

java.util.Set

java.util.TreeMap

java.util.TreeSet

java.util.Vector

java.io.Serializable

javax.jdo.spi.PersistenceCapable

javax.jdo.spi.PersistenceCapable[]

java.lang.Enum

java.lang.Enum[]