org.openmrs.annotation

Annotation Type Handler

@Target(value=TYPE)
 @Retention(value=RUNTIME)
 @Inherited
 @Documented
public @interface Handler

This annotation serves as a general mechanism for providing metadata about a class that serves as a 'Handler' for another class or classes.

This is generally useful for situations where a Handler class has a method that is only valid for certain implementations of a given class, but for which it is not desirable to restrict this method to a given type.

As an example, take Validator class and implementations. As currently designed, a Validator takes in an open-ended Object to validate: public void validate(Object obj, Errors errors)

To provide more context around what type of objects may successfully be passed in here for validation, a Validator also requires implementation of: public boolean supports(Class c)

The weakness of this approach is that the classes that this Validator supports are not exposed. You must first have a class to Validate and check whether it is supported. It would be preferable if each Validator exposed as class metadata the type of Objects that it was capable of Validating. Then, via reflection, much more could be determined about the appropriate Validator for a given object than is currently possible. This is the problem that this annotation aims to solve.

The use of this method would therefore be as follows:

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
int	order Provides a means for specifying the relative order of this Handler against another Handler of the same type.
java.lang.Class<?>[]	supports A list of Classes that this Handler can handle.

Element Detail

supports

public abstract java.lang.Class<?>[] supports

A list of Classes that this Handler can handle.

Returns:

list of classes

Default:

{}

order

public abstract int order

Provides a means for specifying the relative order of this Handler against another Handler of the same type. For example, if two handlers are registered as capable of handling a DateDatatype class, and one handler had an order of 100 and the other had an order of 50, the consuming code could utilize this information to determine which handler is preferred. By convention, the handler with the lowest order generally gains precedence.

Returns:

an int specifying the relative order of this Handler

Default:

2147483647