interface @ConstraintDeclaration
@ConstraintDeclaration is used to create new custom Constraint validators.
Description
Description goes here...
Declaration
package org.qi4j.api.constraint;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* All annotations that are used to trigger Constraints must
* have this annotation.
*/
@Retention( RetentionPolicy.RUNTIME )
@Target( ElementType.ANNOTATION_TYPE )
@Documented
public @interface ConstraintDeclaration
{
}
Example
Let's create a @Range constraint annotation, which can be given a maximum and minimum value that is allowed. First we will need the custom annotation @Range and we need a Constraint implementation.
@ConstraintDeclaration
@Retention( RetentionPolicy.RUNTIME )
@Target( { ElementType.PARAMETER, ElementType.ANNOTATION_TYPE } )
public @interface Range
{
double min();
double max();
}
public class RangeConstraint
implements Constraint<Range, Numeric>
{
public boolean isValid( Range annotation, Numeric object )
{
double argument = object.doubleValue();
return argument >= annotation.min() &&
argument <= annotation.max();
}
}
To use the custom annotation above, we can apply it to a method in a MixinType.
@Constraints( RangeConstraint.class )
public interface AccountCreation
{
Account createAccount( @Range( min=18, max=65 ) int age );
}
public interface AccountCreation
{
Account createAccount( @Range( min=18, max=65 ) int age );
}
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