In this example you will learn how to use ternary operator in Spring Expression Language. The ternary operator will evaluate a Spring EL to one value if a condition is true and to another value if the condition is false. Ternary operator is written using the ?: symbols, just as what you do in Java. The test condition is placed on the left side of the ? symbol while the evaluating expression is placed between the : symbol.
As an example, let’s see how to use the ternary operator in a spring configuration file.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="book1" class="org.kodejava.spring.core.el.Book">
<property name="type" value="Novel" />
</bean>
<bean id="book2" class="org.kodejava.spring.core.el.Book">
<property name="type" value="#{book1.type != null ? book1.type : 'Novel'}" />
</bean>
<bean id="book3" class="org.kodejava.spring.core.el.Book">
<property name="type" value="#{book1.type ?: 'Novel'}" />
</bean>
</beans>
In the configuration you’ll see that there are two ways to use the operator. On the book2 bean we use the common usage of the operator. We check if the book1.type is not equal to null, if this is true then we take the book1.type as the value otherwise we just assign the type to 'Novel'.
There are some duplications in the first example. As you can see, we call the boo1.type twice in that line of code. Actually the Spring EL version can give you a shorter one. Instead of doing like before you can just use the ternary operator like what we use in the book3 bean. So we can type book1.type ?: 'Novel'. This will give us the same result.
Having the configuration created you will also need the Book class. So here is the Book class definition.
package org.kodejava.spring.core.el;
public class Book {
private String type;
public Book() {
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
}
Finally, let’s now create a class to run the spring configuration. This class basically just load the spring configuration file spel-ternary.xml and get some beans, the Book bean from the application context and print out the value of its type property.
package org.kodejava.spring.core.el;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class SpELTernaryOperatorExample {
public static void main(String[] args) {
try (ClassPathXmlApplicationContext context =
new ClassPathXmlApplicationContext("spel-ternary.xml")) {
Book book1 = (Book) context.getBean("book1");
Book book2 = (Book) context.getBean("book2");
Book book3 = (Book) context.getBean("book3");
System.out.println("book1.getType() = " + book1.getType());
System.out.println("book2.getType() = " + book2.getType());
System.out.println("book3.getType() = " + book3.getType());
}
}
}
And here are the execution output that you’ll get.
book1.getType() = Novel
book2.getType() = Novel
book3.getType() = Novel
Maven Dependencies
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>5.3.23</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.3.23</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context-support</artifactId>
<version>5.3.23</version>
</dependency>
</dependencies>
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