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.

1. Bound util namespace.

1. 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"

2. 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

1. 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

1. 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.

1. 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.

1. Below is the above example execution output.

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