= @Parameter
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Collects together all domain semantics of an action parameter within a single annotation.

== API

[source,java]
.Parameter.java
----
@interface Parameter {
  String fileAccept() default "";     // <.>
  int maxLength() default -1;     // <.>
  Class<? extends Specification>[] mustSatisfy() default {};     // <.>
  Optionality optionality() default Optionality.NOT_SPECIFIED;     // <.>
  String regexPattern() default "";     // <.>
  int regexPatternFlags() default 0;     // <.>
  String regexPatternReplacement() default "Doesn't match pattern";     // <.>
  PrecedingParamsPolicy precedingParamsPolicy() default PrecedingParamsPolicy.AS_CONFIGURED;     // <.>
}
----

<.> xref:#fileAccept[fileAccept]
+
--
For uploading xref:refguide:applib:index/value/Blob.adoc[Blob] or xref:refguide:applib:index/value/Clob.adoc[Clob] , optionally restrict the files accepted (eg `.xslx` ).
--
<.> xref:#maxLength[maxLength]
+
--
The maximum entry length of a string parameter (it is ignored for other types).
--
<.> xref:#mustSatisfy[mustSatisfy]
+
--
The xref:refguide:applib:index/spec/Specification.adoc[Specification] (s) to be satisfied by this parameter.
--
<.> xref:#optionality[optionality]
+
--
Whether this parameter is optional or is mandatory (ie required).
--
<.> xref:#regexPattern[regexPattern]
+
--
Regular expression pattern that a value should conform to, and can be formatted as.
--
<.> xref:#regexPatternFlags[regexPatternFlags]
+
--
Pattern flags, as per _java.util.regex.Pattern#compile(String, int)_ .
--
<.> xref:#regexPatternReplacement[regexPatternReplacement]
+
--
Replacement text for the pattern in generated error message.
--
<.> xref:#precedingParamsPolicy[precedingParamsPolicy]
+
--
Whether parameter values should be reset to their default if an earlier parameter changes its value, or whether instead a parameter value, once changed by the end-user, should never be overwritten even if the end-user changes an earlier parameter value.
--

== Members

[#fileAccept]
=== fileAccept

For uploading xref:refguide:applib:index/value/Blob.adoc[Blob] or xref:refguide:applib:index/value/Clob.adoc[Clob] , optionally restrict the files accepted (eg `.xslx` ).

The value should be of the form "file_extension|audio/*|video/*|image/*|media_type".

Note that this does not prevent the user from uploading some other file type; rather it merely defaults the file type in the file open dialog.

[#maxLength]
=== maxLength

The maximum entry length of a string parameter (it is ignored for other types).

The default value ( `-1` ) indicates that no maxLength has been specified.

[#mustSatisfy]
=== mustSatisfy

The xref:refguide:applib:index/spec/Specification.adoc[Specification] (s) to be satisfied by this parameter.

If more than one is provided, then all must be satisfied (in effect "AND"ed together).

[#optionality]
=== optionality

Whether this parameter is optional or is mandatory (ie required).

For parameters the default value, _org.apache.causeway.applib.annotation.Optionality#DEFAULT_ , is taken to mean that the parameter is required.

[#regexPattern]
=== regexPattern

Regular expression pattern that a value should conform to, and can be formatted as.

[#regexPatternFlags]
=== regexPatternFlags

Pattern flags, as per _java.util.regex.Pattern#compile(String, int)_ .

The default value, `0` , means that no flags have been specified.

[#regexPatternReplacement]
=== regexPatternReplacement

Replacement text for the pattern in generated error message.

[#precedingParamsPolicy]
=== precedingParamsPolicy

Whether parameter values should be reset to their default if an earlier parameter changes its value, or whether instead a parameter value, once changed by the end-user, should never be overwritten even if the end-user changes an earlier parameter value.

include::hooks/Parameter_010-examples-and-usage.adoc[]

include::hooks/Parameter_021-optionality.adoc[]

include::hooks/Parameter_022-maxLength.adoc[]

include::hooks/Parameter_023-mustSatisfy.adoc[]

include::hooks/Parameter_024-regexPattern.adoc[]

include::hooks/Parameter_025-fileAccept.adoc[]
