SpEL is a scripting language that allows you to query and manipulate an object graph in real-time. JSP EL, OGNL, MVEL, and JBoss EL are just a few of the expression languages accessible. Method invocation and string templating are two of the extra functionalities provided by SpEL.
API for SpEL: Many interfaces and classes are available in the SpEL API. The following are the details:
- Expression interface
- SpelExpression class
- ExpressionParser interface
- SpelExpressionParser class
- EvaluationContext interface
- StandardEvaluationContext class
Dependencies: Add the following dependencies:
- spring-core
- spring-context
- spring-beans
Implementation: The project structure looks like as depicted in the below media as follows:
A. File: pom.xml
XML
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" <modelVersion>4.0.0</modelVersion> <groupId>com.neveropen.spring</groupId> <artifactId>springListExample</artifactId> <version>0.0.1-SNAPSHOT</version> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>${spring.version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>${spring.version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-beans</artifactId> <version>${spring.version}</version> </dependency> </dependencies> <properties> <spring.version>3.2.3.RELEASE</spring.version> </properties></project> |
Spring Context XML Expression Support
To make the configuration easier, we may employ spring expressions within the XML context. We will start with our example and then move on to the POJO classes.
Here is an example, we are having a training program built around a lesson that covers a variety of technical subjects. The course will focus on a specific subject.
B. File: Topic.java
Java
// Java Program to Illustrate Topic Classpackage com.neveropen.spring;// Classpublic class Topic { // Class data members private String name; // Constructor: Default public Topic() {} // Constructor: Parameterized public Topic(String name) { this.name = name; } // Getters and setters public String getName() { return name; } public void setName(String name) { this.name = name; } public String toString() { return name; }} |
C. File: Tutorial.java
Java
// Java Program to Illustrate Tutorial Classpackage com.neveropen.spring;// Importing required classesimport java.util.ArrayList;import java.util.List;// Classpublic class Tutorial { // Class data members private String name; private List<?> topicsList = new ArrayList<>(); // Getter public String getName() { return name; } // Setter public void setName(String name) { this.name = name; } // Method public List<?> getTopicsList() { return topicsList; } // Setter public void setTopicsList(List<?> topicsList) { this.topicsList = topicsList; } // Method // Overloading toString() method public String toString() { return name + topicsList; }} |
D. File: Training.java
Java
// Java Program to Illustrate Training Classpackage com.neveropen.spring;// Classpublic class Training { // Class data member private Topic topic; // Getter public Topic getTopic() { return topic; } // Setter public void setTopic(Topic topic) { this.topic = topic; }} |
We shall define a couple of technical subjects, java core, and ScalaBasics, as well as a lesson and training, in the context of XML. When defining the beans, SpEL expressions can be combined with XML. #expression string> is the syntax.
#tutorial.topicsList[1] is used to set the topic of our training bean. It sets the subject property to the second topic from the instructional bean’s list of topics.
E. File: applicationContext.xml
XML
<?xml version="1.0" encoding="UTF-8"?> xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:component-scan base-package="com.neveropen.spring" /> <bean id="tutorial" class="com.neveropen.spring.Tutorial"> <property name="topicsList"> <ref local="javaCore" /> <ref local="scalaBasics" /> </property> </bean> <bean id="javaCore" class="com.neveropen.spring.Topic"> <property name="name" value="JavaCore" /> </bean> <bean id="scalaBasics" class="com.neveropen.spring.Topic"> <property name="name" value="ScalaBasics" /> </bean> <bean id="training" class="com.neveropen.spring.Training"> <property name="topic" value="#{tutorial.topicsList[1]}"/> </bean> </beans> |
F. FIle: SpringExpressionXmlContextExample.java
Java
// Java Program to Illustrate Application Classpackage com.neveropen.spring;// Importing required classesimport org.springframework.context.support.ClassPathXmlApplicationContext;// Main Classpublic class SpringExpressionXmlContextExample { // Main driver method public static void main(String[] args) { ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext( "applicationContext.xml"); // Try block to check for exceptions try { Training training = (Training)context.getBean("training"); System.out.println(training.getTopic()); System.out.println(training.getDefaultTopic()); } // finally block that will execute for sure finally { // Closing the connections // using close() method context.close(); } }} |
Output:
ScalaBasics
Annotation in Spring Expressions
SpEL expressions may also be used to define beans using annotation-based configuration metadata. To define a default value, use the @Value annotation on fields, methods, and method/constructor arguments.
We’ve added a new member defaultTopic to our Training bean to show the example. To set the defaultTopic, we utilized a spring expression.
File: Training.java
Java
package com.neveropen.spring; import org.springframework.beans.factory.annotation.Value; public class Training{ private Topic topic; @Value("#{tutorial.topicsList[0]}") private Topic defaultTopic; //getters and setters public Topic getTopic() { return topic; } public void setTopic(Topic topic) { this.topic = topic; } public Topic getDefaultTopic() { return defaultTopic; }} |
The annotations are scanned and assessed by adding the context: the component-scan element to the context XML.
File: applicationContext.xml
XML
<?xml version="1.0" encoding="UTF-8"?> xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd"> <context:component-scan base-package="com.neveropen.spring" /> <bean id="tutorial" class="com.neveropen.spring.Tutorial"> <property name="topicsList"> <ref local="javaCore" /> <ref local="scalaBasics" /> </property> </bean> <bean id="javaCore" class="com.neveropen.spring.Topic"> <property name="name" value="JavaCore" /> </bean> <bean id="scalaBasics" class="com.neveropen.spring.Topic"> <property name="name" value="ScalaBasics" /> </bean> <bean id="training" class="com.neveropen.spring.Training"> <property name="topic" value="#{tutorial.topicsList[1]}"/> </bean> </beans> |
Let’s see whether defaultTopic is enabled.
File: SpringExpressionXmlContextExample.java
Java
package com.neveropen.spring;import org.springframework.context.support.ClassPathXmlApplicationContext;public class SpringExpressionXmlContextExample { public static void main(String[] args) { ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext( "applicationContext.xml"); try { Training training = (Training) context.getBean("training"); System.out.println(training.getTopic()); System.out.println(training.getDefaultTopic()); } finally { context.close(); } }} |
Output:
ScalaBasics JavaCore
Spring Expression Language Parser Example
Using the expression parser, the SpEL may also be utilized as a standalone component.
org.springframework.expression.spel.standard.SpelExpressionParser.
File: SpringExpressionParserExample.java
Java
package com.neveropen.spring;import org.springframework.expression.Expression;import org.springframework.expression.spel.standard.SpelExpressionParser;public class SpringExpressionParserExample { public static void main(String[] args) { SpelExpressionParser parser = new SpelExpressionParser(); Expression exp = parser.parseExpression("'Just a string value'"); String message = (String) exp.getValue(); System.out.println(message); System.out.println(parser.parseExpression("'Just a string value'.substring(5)").getValue()); System.out.println(parser.parseExpression("'Just a string value'.length()").getValue()); System.out.println(parser.parseExpression("'Just a string value'.substring('Just '.length())").getValue()); System.out.println(parser.parseExpression("'Just a string value'.class").getValue()); System.out.println(parser.parseExpression("'Just a string value'.bytes").getValue()); System.out.println(parser.parseExpression("new com.neveropen.spring.Topic('Java')").getValue(Topic.class).getClass()); }} |
Output:
Let’s have a look at a couple more instance: Using Spring ExpressionParser to call a method where in this example, we call String‘s substring(), length().
File: SpringExpressionParserExample.java
Java
package com.neveropen.spring;import java.util.Arrays;import org.springframework.expression.EvaluationContext;import org.springframework.expression.Expression;import org.springframework.expression.spel.standard.SpelExpressionParser;import org.springframework.expression.spel.support.StandardEvaluationContext; public class SpringExpressionParserExample { public static void main(String[] args) { SpelExpressionParser parser = new SpelExpressionParser(); Expression exp = parser.parseExpression("'Just a string value'"); String message = (String) exp.getValue(); System.out.println(message); System.out.println(parser.parseExpression("'Just a string value'.substring(5)").getValue()); System.out.println(parser.parseExpression("'Just a string value'.length()").getValue()); System.out.println(parser.parseExpression("'Just a string value'.substring('Just '.length())").getValue()); }} |
Output:
Access JavaBean Properties using Spring ExpressionParser
Let’s access a couple of JavaBean properties classes and bytes of the String objects.
File: SpringExpressionParserExample.java
Java
// Java Program to Illustrate Spring Expression Parserpackage com.neveropen.spring;// Importing required classesimport java.util.Arrays;import org.springframework.expression.EvaluationContext;import org.springframework.expression.Expression;import org.springframework.expression.spel.standard.SpelExpressionParser;import org.springframework.expression.spel.support.StandardEvaluationContext;// Classpublic class SpringExpressionParserExample { // Main driver method public static void main(String[] args) { SpelExpressionParser parser = new SpelExpressionParser(); Expression exp = parser.parseExpression( "'Just a string value'"); String message = (String)exp.getValue(); // Print commands System.out.println(message); System.out.println( parser .parseExpression( "'Just a string value'.substring(5)") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.length()") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.substring('Just '.length())") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.class") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.bytes") .getValue()); }} |
Output:
Calling Constructor using Spring ExpressionParser
We can create an object by calling the constructor of the class in the spring expression. For example:
'new com.neveropen.spring.Topic('Java')'
File: SpringExpressionParserExample.java
Java
// Java Program to Illustrate Spring Expression Parserpackage com.neveropen.spring;// Importing required classesimport java.util.Arrays;import org.springframework.expression.EvaluationContext;import org.springframework.expression.Expression;import org.springframework.expression.spel.standard.SpelExpressionParser;import org.springframework.expression.spel.support.StandardEvaluationContext;// Classpublic class SpringExpressionParserExample { // Main driver method public static void main(String[] args) { SpelExpressionParser parser = new SpelExpressionParser(); Expression exp = parser.parseExpression( "'Just a string value'"); String message = (String)exp.getValue(); System.out.println(message); // Print commands System.out.println( parser .parseExpression( "'Just a string value'.substring(5)") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.length()") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.substring('Just '.length())") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.class") .getValue()); System.out.println( parser .parseExpression( "'Just a string value'.bytes") .getValue()); System.out.println( parser .parseExpression( "new com.neveropen.spring.Topic('Java')") .getValue(Topic.class) .getClass()); }} |
Output:
