Creating a Spring Bean from a Java 5 Enum

Instances of Java enums, introduced in Java 5, can be a bit tricky to instantiate as Spring beans because the Java compiler hides enum constructors. However, we can create a bean from an enum by using the enum valueOf static method as a factory method.

For example, let's say we have defined an enum class as follows:

package robertmaldon.cafe;

public enum Coffee {
    MOCHA,
    ESPRESSO,
    LATTE,
    FRAPPUCCINO;
}

The Spring XML config for a bean instance then looks something like this:

 <bean id="latte" class="robertmaldon.cafe.Coffee" factory-method="valueOf">
     <constructor-arg>
         <value>LATTE</value>
     </constructor-arg>
 </bean>

NOTE: Declaring the bean scope as prototype or singleton makes no difference. For the same class loader a singleton bean is always returned.

If you don't want to declare a bean for each value of an enum you can simply use the enum value name at the point where it is injected into a dependent class. For example, let's say you have a class that is injected with an instance of our enum above:

package robertmaldon.cafe;

public class CoffeeMachine {
    private Coffee coffee;
    
    public void setCoffee(Coffee coffee) {
        this.coffee = coffee;
    }
}

In the Spring XML config simply use the enum value as the property value (apparently works with Spring 1.2.2 and beyond):

    <bean id="machine" class="robertmaldon.cafe.CoffeeMachine">
        <property name="coffee" value="MOCHA"/>
    </bean>