Test Spring el with ExpressionParser

Spring expression language (SpEL) supports many functionality, and you can test those expression features with this special “ExpressionParser” interface.

Here’s two code snippets, show the basic usage of using Spring EL.

SpEL to evaluate the literal string expression.

ExpressionParser parser = new SpelExpressionParser();
Expression exp = parser.parseExpression("'put spel expression here'");
String msg = exp.getValue(String.class);

SpEL to evaluate the bean property – “item.name”.

Item item = new Item("mkyong", 100);
StandardEvaluationContext itemContext = new StandardEvaluationContext(item);

//display the value of item.name property
Expression exp = parser.parseExpression("name");
String msg = exp.getValue(itemContext, String.class);

Few examples to test SpEL. The codes and comments should be self-exploratory.

import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;

public class App {
	public static void main(String[] args) {

		ExpressionParser parser = new SpelExpressionParser();

		//literal expressions
		Expression exp = parser.parseExpression("'Hello World'");
		String msg1 = exp.getValue(String.class);
		System.out.println(msg1);

		//method invocation
		Expression exp2 = parser.parseExpression("'Hello World'.length()");
		int msg2 = (Integer) exp2.getValue();
		System.out.println(msg2);

		//Mathematical operators
		Expression exp3 = parser.parseExpression("100 * 2");
		int msg3 = (Integer) exp3.getValue();
		System.out.println(msg3);

		//create an item object
		Item item = new Item("mkyong", 100);
		//test EL with item object
		StandardEvaluationContext itemContext = new StandardEvaluationContext(item);

		//display the value of item.name property
		Expression exp4 = parser.parseExpression("name");
		String msg4 = exp4.getValue(itemContext, String.class);
		System.out.println(msg4);

		//test if item.name == 'mkyong'
		Expression exp5 = parser.parseExpression("name == 'mkyong'");
		boolean msg5 = exp5.getValue(itemContext, Boolean.class);
		System.out.println(msg5);

	}
}

public class Item {

	private String name;

	private int qty;

	public Item(String name, int qty) {
		super();
		this.name = name;
		this.qty = qty;
	}

	//...
}

Output

Hello World
11
200
mkyong
true