org.apache.cassandra.cql3.functions.IGenericFunction Maven / Gradle / Ivy
package org.apache.cassandra.cql3.functions;
import org.apache.commons.lang3.reflect.FieldUtils;
/**
* CQL function taking arbitrary types.
*
*/
public interface IGenericFunction extends Function
{
/**
* GenericFunction should declare a public static class implementing IGenericFunction.Loader with a public constructor with no arguments.
* Then, by declaring this inner class in META-INF/services/org.apache.cassandra.cql3.functions.IGenericFunction$Loader,
* generic function will be registred by a ServiceLoader in GenericFunctionRegistry..
* This allows to drop a jar defining custom generic CQL functions in the Cassandra classpath.
*/
public interface Loader
{
public default void register(Class clazz) throws IllegalAccessException
{
// generic function should always have a public static FunctionName NAME field.
FunctionName functionName = (FunctionName) FieldUtils.readDeclaredStaticField(clazz, "NAME");
GenericFunctionRegistry.registerFunction(functionName, clazz);
}
// could be overridden if Loader in not an inner class of the generic function.
public default Class getGenericFunctionClass()
{
return this.getClass().getDeclaringClass();
}
}
}