= Java EE Annotations

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While Apache Isis does define many of its own annotations, the policy is to reuse standard Java/JEE annotations wherever they exist or are added to the Java platform.

The table below lists the JEE annotations currently recognized.  Expect to see more added in future releases of Apache Isis.


.Java EE Annotations
[cols="2,4a,1,1", options="header"]
|===
|Annotation
|Purpose
|Layer
|xref:userguide:fun:ui.adoc#object-layout[File-based layout]?

|xref:refguide:applib-ant:Digits.adoc[`@javax.validation.` +
`constraints.` +
`Digits`]
|Precision/scale for BigDecimal values.
|Domain
|

|xref:refguide:applib-ant:Pattern.adoc[`@javax.validation.` +
`constraints.` +
`Pattern`]
|Regular expressions for strings
|Domain
|


|xref:refguide:applib-ant:Digits.adoc[`@javax.annotation.` +
`Nullable`]
|Specify that a property/parameter is optional.
|Domain
|


|xref:refguide:applib-ant:XmlRootElement.adoc[`javax.xml.bind` +
`.annotation` +
`XmlRootElement`]
|JAXB annotation indicating the XML root element when serialized to XML; also used by the framework for view models (whose memento is the XML), often also acting as a DTO.
|Application
|

|xref:refguide:applib-ant:XmlJavaTypeAdapter.adoc[`javax.xml.bind` +
`.annotation` +
`XmlJavaTypeAdapter`]
|JAXB annotation defining how to serialize an entity.  Used in conjunction with the (framework provided) `PersistentEntityAdapter` class to serialize persistent entities into a canonical OID (equivalent to the `Bookmark` provided by the xref:refguide:applib:index/services/bookmark/BookmarkService.adoc[BookmarkService]).
|Domain
|


|===



