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 Spring > Expression Language > List Projection

List Projection 

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 projection operator (![projectionExpression]). It helps to evaluate a sub expression against the given collection and the result is a new collection.

File Name  :  
com/bethecoder/tutorials/spring3/tests/spel/ListProjectionTest.java 
Author  :  Sudhakar KV
Email  :  kvenkatasudhakar@gmail.com
   
package com.bethecoder.tutorials.spring3.tests.spel;

import java.util.ArrayList;
import java.util.List;

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 ListProjectionTest {

  /**
   @param args
   */
  public static void main(String[] args) {

    StandardEvaluationContext stdContext = new StandardEvaluationContext();
    List<Employee> employees = new ArrayList<Employee>();
    employees.add(new Employee(1"ONE"1111));
    employees.add(new Employee(2"TWO"2222));
    employees.add(new Employee(3"THREE"3333));
    employees.add(new Employee(4"FOUR"4444));
    employees.add(new Employee(5"FIVE"5555));
    employees.add(new Employee(6"SIX"6666));
    
    stdContext.setVariable("emps", employees);
    
    ExpressionParser parser = new SpelExpressionParser();
    List<String> proj = (List<String>parser.parseExpression(
        "#emps.![name]").getValue(stdContext);
    System.out.println(proj)
    
    proj = (List<String>parser.parseExpression(
        "#emps.!['X-' + name.toLowerCase()]").getValue(stdContext);
    System.out.println(proj);
  }

}
   

It gives the following output,
[ONE, TWO, THREE, FOUR, FIVE, SIX]
[X-one, X-two, X-three, X-four, X-five, X-six]


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