Use util:constant To Declare Final Static Field As Spring Bean

Spring tag util:constant can be used to declare a bean that references one class’s final static field. This article will show you how to do that.

Table of Contents

1. Bound util namespace.

To use util:constant, you should first bound the util namespace for beans tag in application context XML file ( BeanSettings.xml ) as below.
```
xmlns:util="http://www.springframework.org/schema/util"
```

Below is the entire BeanSettings.xml file content.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:util="http://www.springframework.org/schema/util"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
</beans>

2. Create CarBrand.java

This is java class represent car brand. It has two final static filed which are AUDI_BRAND and FORD_BRAND, the two fields will be referenced later.

public class CarBrand {
	
	public final static CarBrand AUDI_BRAND = new CarBrand("Audi" , "Germany");
	
	public final static CarBrand FORD_BRAND = new CarBrand("Ford" , "United States");

	private String brandName;
	
	private String brandCountry;

	public String getBrandName() {
		return brandName;
	}

	public void setBrandName(String brandName) {
		this.brandName = brandName;
	}

	public String getBrandCountry() {
		return brandCountry;
	}

	public void setBrandCountry(String brandCountry) {
		this.brandCountry = brandCountry;
	}

	public CarBrand(String brandName, String brandCountry) {
		super();
		this.brandName = brandName;
		this.brandCountry = brandCountry;
	}

	@Override
	public String toString() {
		StringBuffer retBuf = new StringBuffer();
		
		retBuf.append("Brand Name : " + this.getBrandName());
		
		retBuf.append(" , Brand Country : " + this.getBrandCountry());
		
		return retBuf.toString();
	}
}

3. Create CarFactory.java

This class represents a car factory that will produce Audi and Ford cars. It has two properties for Audi brand and Ford brand car.

public class CarFactory {
	
	private CarBrand audiBrand;
	
	private CarBrand fordBrand;
	
	public CarBrand getAudiBrand() {
		return audiBrand;
	}

	public void setAudiBrand(CarBrand audiBrand) {
		this.audiBrand = audiBrand;
	}

	public CarBrand getFordBrand() {
		return fordBrand;
	}

	public void setFordBrand(CarBrand fordBrand) {
		this.fordBrand = fordBrand;
	}

	public static void main(String[] args) {
		
	   	// Initiate Spring application context, this line code will invoke bean initialize method.
		ApplicationContext springAppContext = new ClassPathXmlApplicationContext("BeanSettings.xml");

		// Get the car factory bean.
		CarFactory carFactory = (CarFactory)springAppContext.getBean("carFactoryBean");
		
		System.out.println(carFactory.getAudiBrand().toString());
		
		System.out.println(carFactory.getFordBrand().toString());
	}

}

4. Use util:constant to declare beans.

The util:constant tag’s static-field attribute value is just the CarBrand class’s final static field AUDI_BRAND or FORD_BRAND.

<util:constant id="audiBrand" static-field="com.dev2qa.example.spring.bean.finalstatic.CarBrand.AUDI_BRAND" /> 

<util:constant id="fordBrand" static-field="com.dev2qa.example.spring.bean.finalstatic.CarBrand.FORD_BRAND" /> 

<bean id="carFactoryBean" class="com.dev2qa.example.spring.bean.finalstatic.CarFactory"> 

      <property name="audiBrand" ref="audiBrand"></property> 

      <property name="fordBrand" ref="fordBrand"></property> 
</bean>

5. Output.

Below is the above example execution output.

Brand Name : Audi , Brand Country : Germany
Brand Name : Ford , Brand Country : United States

6. Questions & Answers.

6.1