Spring util:constant tag can be used to declare a bean which reference one class’s final static field. This article will show you how to do that.
1.Bound util namespace.
To use util:constant, you should first bound the util namespace for beans tag in application context xml file as below.
xmlns:util="http://www.springframework.org/schema/util"
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 field 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 represent a car factory which 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
