@Target(value=TYPE) @Retention(value=RUNTIME) @Constraint(validatedBy=ScriptAssertValidator.class) @Documented public @interface ScriptAssert
A class-level constraint, that evaluates a script expression against the annotated element. This constraint can be used to implement validation routines, that depend on multiple attributes of the annotated element.
For evaluation of expressions the Java Scripting API as defined by JSR 223 ("Scripting for the JavaTM Platform") is used. Therefore an implementation of that API must part of the class path. This is automatically the case when running on Java 6. For older Java versions, the JSR 223 RI can be added manually to the class path.
The expressions to be evaluated can be written in any scripting or expression language, for which a JSR 223 compatible engine can be found in the class path. The following listing shows an example using the JavaScript engine, which comes with Java 6:@ScriptAssert(lang = "javascript", script = "_this.startDate.before(_this.endDate)") public class CalendarEvent { private Date startDate; private Date endDate; //... }
Using a real expression language in conjunction with a shorter object alias allows for very compact expressions:
@ScriptAssert(lang = "jexl", script = "_.startDate < _.endDate", alias = "_") public class CalendarEvent { private Date startDate; private Date endDate; //... }
Accepts any type.
public abstract String lang
ScriptEngineManager
. A
ConstraintDeclarationException
will be thrown upon script
evaluation, if no engine for the given language could be found.public abstract String script
Boolean.TRUE
, if the annotated element could
successfully be validated, otherwise Boolean.FALSE
.
Returning null or any type other than Boolean will cause a
ConstraintDeclarationException
upon validation. Any
exception occurring during script evaluation will be wrapped into
a ConstraintDeclarationException, too. Within the script, the
validated object can be accessed from the script context
using the name specified in the
alias
attribute.public abstract String message
public abstract Class<?>[] groups
public abstract String alias
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