Map Selection
The Spring Expression Language (SpEL ) is a simple and powerful expression language
which helps to query and manipulate objects at runtime.
The following example shows using selection operator (?[selectionExpression] ).
It filters the collection and returns a new collection containing a subset of the original elements.
The selection criteria is evaluated against each individual map entry (Map.Entry).
package com.bethecoder.tutorials.spring3.tests.spel; import java.util.HashMap; import java.util.Map; import org.springframework.expression.ExpressionParser; import org.springframework.expression.spel.standard.SpelExpressionParser; import org.springframework.expression.spel.support.StandardEvaluationContext; import com.bethecoder.tutorials.spring3.basic.Employee; public class MapSelectionTest { /** * @param args */ public static void main ( String [] args ) { StandardEvaluationContext stdContext = new StandardEvaluationContext () ; Map<Integer, Employee> employees = new HashMap<Integer, Employee> () ; employees.put ( 1 , new Employee ( 1 , "ONE" , 1111 )) ; employees.put ( 2 , new Employee ( 2 , "TWO" , 2222 )) ; employees.put ( 3 , new Employee ( 3 , "THREE" , 3333 )) ; employees.put ( 4 , new Employee ( 4 , "FOUR" , 4444 )) ; employees.put ( 5 , new Employee ( 5 , "FIVE" , 5555 )) ; employees.put ( 6 , new Employee ( 6 , "SIX" , 6666 )) ; stdContext.setVariable ( "empMap" , employees ) ; /** * Employees having salary greater than 4000 */ ExpressionParser parser = new SpelExpressionParser () ; Map<Integer, Employee> subSet = ( Map<Integer, Employee> ) parser.parseExpression ( "#empMap.?[value.salary > 4000]" ) .getValue ( stdContext ) ; System.out.println ( subSet ) ; /** * Employees having salary less than 4000 */ subSet = ( Map<Integer, Employee> ) parser.parseExpression ( "#empMap.?[value.salary < 4000]" ) .getValue ( stdContext ) ; System.out.println ( subSet ) ; } }
{4=Employee[4, FOUR, 4444.0], 5=Employee[5, FIVE, 5555.0], 6=Employee[6, SIX, 6666.0]}
{1=Employee[1, ONE, 1111.0], 2=Employee[2, TWO, 2222.0], 3=Employee[3, THREE, 3333.0]}
