Advertisement

---

Top

< Prev

Next >

In this tutorial, we will explain how Spring Expression Language(SpEL) allows us to define new variables, which could be used to set values of the properties associated with an object of a class. In order to define such variables :

• We will first use setVariable() method of StandardEvaluationContext class, which is used to set/define new variables with values in a context of an object.


• Next, these variables are used in the String expressions, using #VariableName syntax and are passed to the method parseRaw() of SpelExpressionParse class, which parses the variable in String expression and returns an expression in the form of an object of SpelExpression class.


• Lastly, we will call getValue() method of SpelExpression class, which evaluates this expression in the provided context and return the result of evaluation. i.e. it gets the result of expression and sets the property associated with the object(being evaluated) with the value of the variable.

Let's see an example explaining how to define some new variables and use their values to set the values of the properties of a class, using Spring Expression Language(SpEL).

Creating a Java Class - Employee

We are going to create a Java class named Employee within the decodejava package and this class is going to contain a few properties, such as -

• A String property named - name.
• A primitive int property named - telNo.
• A primitive char property named - positionGrade.
• A primitive float property named - yearsOfExp.
• A static String property named - message.

Besides this, we are also going to define a couple of getter and setter methods for these properties.

package decodejava;

public class Employee 
{
	private String name;
	private int telNo;
	private char positionGrade;
	private float yearsOfExp;
	static String message;
	
	
	public static String getMessage() 
	{
		return message;
	}

	public static void setMessage(String message) 
	{
		Employee.message = message;
	}

	
	public char getPositionGrade() 
	{
		return positionGrade;
	}

	public void setPositionGrade(char positionGrade) 
	{
		this.positionGrade = positionGrade;
	}

	public float getYearsOfExp() 
	{
		return yearsOfExp;
	}

	public void setYearsOfExp(float yearsOfExp) 
	{
		this.yearsOfExp = yearsOfExp;
	}
	
	
	public String getName() 
	{
		return name;
	}
	
	public void setName(String name) 
	{
		this.name = name;
	}
	
	public int getTelNo() {
		return telNo;
	}
	
	public void setTelNo(int telNo) 
	{
		this.telNo = telNo;
	}
}

Advertisement

Adding the Utility class that calls the Spring API

Next, we are going to create another java class named - Utility.

Utility.java

package decodejava;

import org.springframework.expression.spel.standard.SpelExpression;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;

public class Utility {

	public static void main(String[] args) 
	{
		Employee employee = new Employee();
		
		StandardEvaluationContext  stContext  = new StandardEvaluationContext(employee);
		stContext.setVariable("EmpName", "Employee1");
		stContext.setVariable("EmpTelephoneNo", 1111111);
		stContext.setVariable("EmpPositionGrade", "A");
		stContext.setVariable("EmpExperience", 6.7);
		stContext.setVariable("EmpMessage", "Best of luck!");
		
		SpelExpressionParser parser = new SpelExpressionParser();
		
		SpelExpression expression = parser.parseRaw("name=#EmpName");
		expression.getValue(stContext);
		System.out.println("Employee's Name :  " + employee.getName());
		
		
		expression = parser.parseRaw("telNo=#EmpTelephoneNo");
		expression.getValue(stContext);
		System.out.println("Employee's Telephone number : " + employee.getTelNo());	
		
		
		expression = parser.parseRaw("positionGrade=#EmpPositionGrade");
		expression.getValue(stContext);
		System.out.println("Employee's Position Grade :  " + employee.getPositionGrade());
		
		
		expression = parser.parseRaw("yearsOfExp=#EmpExperience");
		expression.getValue(stContext);
		System.out.println("Employee's Years Of Exp : " + employee.getYearsOfExp());
		
		
		expression = parser.parseRaw("message=#EmpMessage");
		expression.getValue(stContext);
		System.out.println("Message for employee : " + employee.getMessage());
	
	}
}

In this class we have first created an object of Employee class and performed the next few steps -

• We have used StandardEvaluationContext class which evaluates an expression in the context of an object of Employee class.


• Next, we have called setVariable() method of StandardEvaluationContext class, which is used to set/define new variables with values.


• Next, these variables are used in the String expressions, using #VariableName syntax and are passed to the method parseRaw() of SpelExpressionParse class, which parses the variable in String expression and returns an expression in the form of an object of SpelExpression class.


• Lastly, we will call getValue() method of SpelExpression class, which evaluates this expression in the provided context and return the result of evaluation. i.e. it gets the result of expression and sets the property associated with the object of Employee class(being evaluated) with the value of the variable.

Directory Structure of Project

The picture above depicts how and where to arrange classes and interfaces comprising this Spring Project, in a specific directory structure.

Project Folder - SpELVariables is the name of our Project and it is a top-level directory.

This project folder contains a package of our project i.e. decodejava containing three classes -
• A POJO class named Employee.java.
• A class that calls the Spring Framework into action i.e. Utility.java.



• Besides this, the project folder also contains a configuration file i.e. config.beans.xml, used to configure the beans of classes in the project.
  
  
• The project folder also contains all the needed Spring JARs present in the libs folder of Spring Framework installation.

Execution

Finally, after executing Utility class, you will get the following output within the Console window.

Employee's Name :  Employee1
Employee's Telephone number : 1111111
Employee's Position Grade :  A
Employee's Years Of Exp : 6.7
Message for employee : Best of luck!

This output shown below, shows the values of properties associated with an object of Employee class. These properties were set with the values of variables created using Spring Expression Language(SpEL).

Please share this article -

< Prev

Next >

< Spring Expression Language(SpEL)

SpEL Operators >

Advertisement