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

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package de.japkit.metaannotations;

public @interface Var {
	String name() default "";
	
	/**
	 * If true, the variable is not set if it already exists and is not null or empty.
	 * @return
	 */
	boolean ifEmpty() default false;

	/**
	 * 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, a function can be called to calculate the value for the variable.
	 * 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 {};
	
	
	/**
	 * Allows to instantiate an arbitrary bean and assign it to the variable. The class must be on the annotation processors classpath and must have a no-arg constructor.
	 * @return
	 */
	Class[] bean() default {};
	
	/**
	 * Allows to instantiate an arbitrary class to the variable, for example to access their static members. The class must be on the annotation processors classpath.
	 * @return
	 */
	Class[] beanClass() default {};
	

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


	
	@interface List {
		Var[] value();
	}
}