de.japkit.metaannotations.Function Maven / Gradle / Ivy

Go to download
package de.japkit.metaannotations;


public @interface Function {

	/**
	 * The expression to be evaluated.
	 * 
	 * @return
	 */
	String expr() default "";

	/**
	 * The language for the expression.
	 * @return
	 */
	String lang() default "";
	
	/**
	 * As an alternative or additionally to the expression, another function can be called.
	 * In case of more than one function, they are called in a "fluent" style. That is each one is applied to the result of the previous one.
	 * The first function is always applied to the result of the expr or to the current "src" if expr is empty. 
	 * 
	 * @return
	 */
	Class[] fun() default {};
	
	/**
	 * A filter expression to be applied to the result of the expression or function(s) in case it is a collection. Must be boolean. 
	 * The variable name for the current collection element to be filtered is "src". 
	 * @return
	 */
	String filter() default "";

	/**
	 * As an alternative to filter, one or more boolean functions can be called. 
	 * Only if the conjunction of their results is true, the rule is applied for the considered element of the src collection.
	 * 
	 * @return
	 */
	Class[] filterFun() default {};
	
	/**
	 * An expression to be applied to the result of the expression or function(s) in case it is a collection. It's applied to each element.
	 * The variable name for the current collection element is "src". Collect is applied after filtering.
	 * 
	 * @return
	 */
	String collect() default "";

	/**
	 * As an alternative or additionally to the collect expression, one or more functions can be called. 
	 * In case of more than one function, they are called in a "fluent" style. That is each one is applied to the result of the previous one. 
	 * The first function is always applied to the result of the collect expression or to the current collection element if collect expression is empty.
	 *  
	 * @return
	 */
	Class[] collectFun() default {};
	
	/**
	 * If true, and src is a collection, it is transformed to a LinkedHashSet to remove duplicates while preserving order.
	 * 
	 * @return
	 */
	boolean toSet() default false;
	
	/**
	 * If src is a collection, and groupBy and / or groupByFun are set, the collection elements are grouped as a map, where 
	 * the keys are the results of applying groupBy and / or groupByFun to the collection elements and the values are lists 
	 * of collection elements with same key. groupBy is an expression and groupByFun is a list of functions. 
	 * They are applied in a fluent style (like src.groupBy().groupByFun[0]().groupByFun[1]()...).
	 * 
	 * @return the expression to derive the key from a collection element. The collection element is provided as "src".
	 */
	String groupBy() default "";
	

	/**
	 * If src is a collection, and groupBy and / or groupByFun are set, the collection elements are grouped as a map, where 
	 * the keys are the results of applying groupBy and / or groupByFun to the collection elements and the values are lists 
	 * of collection elements with same key. groupBy is an expression and groupByFun is a list of functions. 
	 * They are applied in a fluent style (like src.groupBy().groupByFun[0]().groupByFun[1]()...).
	 * 
	 * @return function(s) to derive the key from a collection element. The collection element is provided as "src".
	 */
	Class[] groupByFun() default {};
	
	/**
	 * 
	 * @return true means, that only the first element of the collection is returned and it is an error if there are multiple. 
	 * If the collection is empty, null is returned (which might result in an error depending on {@link #nullable()}).
	 */
	boolean unique() default false;
	

	Class type() default Object.class;
	
	/**
	 * Whether the result of the function might be null. By default, this is not allowed.
	 * @return
	 */
	boolean nullable() default false;


	
}