SPEL : Spring Expression Language Tutorial

Spring Expression Language Tutorial

SpEL is an exression language supporting the features of querying and manipulating an object graph at runtime.

There are many expression languages available such as JSP EL, OGNL, MVEL and JBoss EL. SpEL

provides some additional features such as method invocation and string templating functionality.

SpEL API

The SpEL API provides many interfaces and classes. They are as follows:

• Expression interface
• SpelExpression class
• ExpressionParser interface
• SpelExpressionParser class
• EvaluationContext interface
• StandardEvaluationContext class

SPEL Example

import org.springframework.expression.Expression;

 import org.springframework.expression.ExpressionParser;

import org.springframework.expression.spel.standard.SpelExpressionParser;

public class Test {

public static void main(String[] args) {

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("'Hello SPEL'");

String message = (String) exp.getValue();

System.out.println(message);

//OR

//System.out.println(parser.parseExpression("'Hello SPEL'").getValue());

}

}

Using concat() method with String

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("'Welcome SPEL'.concat('!')");

String message = (String) exp.getValue();

System.out.println(message);

Converting String into byte array

Expression exp = parser.parseExpression("'Hello World'.bytes");

byte[] bytes = (byte[]) exp.getValue();

for(int i=0;i<bytes.length;i++){

System.out.print(bytes[i]+" ");

}

Getting length after converting string into bytes

Expression exp = parser.parseExpression("'Hello World'.bytes.length");

int length = (Integer) exp.getValue();

System.out.println(length);

Converting String contents into uppercase letter

Expression exp = parser.parseExpression("new String('hello world').toUpperCase()");

String message = exp.getValue(String.class);

System.out.println(message);

//OR

System.out.println(parser.parseExpression("'hello world'.toUpperCase()").getValue());

Operators in SPEL

We can use many operators in SpEL such as arithmetic, relational, logical etc. There are given a lot of examples of using different operators in SpEL.

import org.springframework.expression.ExpressionParser;

import org.springframework.expression.spel.standard.SpelExpressionParser;

 public class Test {

 public static void main(String[] args) {

 ExpressionParser parser = new SpelExpressionParser();

 //arithmetic operator

System.out.println(parser.parseExpression("'Welcome SPEL'+'!'").getValue());

 System.out.println(parser.parseExpression("10 * 10/2").getValue());

 System.out.println(parser.parseExpression("'Today is: '+ new java.util.Date()").getValue());

 //logical operator

 System.out.println(parser.parseExpression("true and true").getValue());

 //Relational operator

 System.out.println(parser.parseExpression("'Piyush'.length()==5").getValue());

 }

 }

Variable in SPEL | StandardEvaluationContext

In SpEL, we can store a value in the variable and use the variable in the method and call the method. To work on variable, we need to use StandardEvaluationContext class.

Example of Using variable in SPEL

Calculation.java

public class Calculation {

private int number;

public int getNumber() {

return number;

}

public void setNumber(int number) {

this.number = number;

}

public int cube(){

return number*number*number;

}

}

Test.java

import org.springframework.expression.ExpressionParser;

import org.springframework.expression.spel.standard.SpelExpressionParser;

import org.springframework.expression.spel.support.StandardEvaluationContext;

public class Test {

public static void main(String[] args) {

Calculation calculation=new Calculation();

StandardEvaluationContext context=new StandardEvaluationContext(calculation);

ExpressionParser parser = new SpelExpressionParser();

 parser.parseExpression("number").setValue(context,"5");

 System.out.println(calculation.cube());

 }

 }