Collection Selection

Selection is a powerful expression language feature that lets you transform a source collection into another collection by selecting from its entries.

Selection uses a syntax of .?[selectionExpression]. It filters the collection and returns a new collection that contains a subset of the original elements. For example, selection lets us easily get a list of Serbian inventors, as the following example shows:

Selection is supported for arrays and anything that implements java.lang.Iterable or java.util.Map. For a list or array, the selection criteria is evaluated against each individual element. Against a map, the selection criteria is evaluated against each map entry (objects of the Java type Map.Entry). Each map entry has its key and value accessible as properties for use in the selection.

The following expression returns a new map that consists of those elements of the original map where the entry’s value is less than 27:

In addition to returning all the selected elements, you can retrieve only the first or the last element. To obtain the first element matching the selection, the syntax is .^[selectionExpression]. To obtain the last matching selection, the syntax is .$[selectionExpression].