XML Based Bean Configuration: Constructor Injection : Constructor Injection « Spring « Java Tutorial

1. Java Tutorial
2. Spring
3. Constructor Injection

File: context.xml

<?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
                http://www.springframework.org/schema/util
                http://www.springframework.org/schema/util/spring-util.xsd">

    <bean id="encyclopedia"
          name="knowitall"
          class="ConfigurableEncyclopedia">
        <constructor-arg>
            <util:map>
                <entry key="AgeOfUniverse" value="13700000000"/>
                <entry key="ConstantOfLife" value="326190476"/>
            </util:map>
        </constructor-arg>
    </bean>

    <bean id="oracle" class="BookwormOracle">
        <property name="encyclopedia" ref="knowitall"/>
    </bean>

</beans>

File: Main.java

import java.util.Map;

import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.util.Assert;

public class Main {
  public static void main(String[] a) {
    XmlBeanFactory bf = new XmlBeanFactory(new ClassPathResource("context.xml"));

    Oracle oracle = (Oracle) bf.getBean("oracle");
    System.out.println("Meaning of life is " + oracle.defineMeaningOfLife());
  }
}

interface Oracle {

  String defineMeaningOfLife();

}
interface Encyclopedia {

  Long findLong(String entry);
  
}
class BookwormOracle implements Oracle {
  private Encyclopedia encyclopedia;

  public String defineMeaningOfLife() {
      Long ageOfUniverse = this.encyclopedia.findLong("AgeOfUniverse");
      Long constantOfLife = this.encyclopedia.findLong("ConstantOfLife");
      return String.valueOf(ageOfUniverse / constantOfLife);
  }

  public void setEncyclopedia(Encyclopedia encyclopedia) {
      this.encyclopedia = encyclopedia;
  }
}

class ConfigurableEncyclopedia implements Encyclopedia {
  private Map<String, Long> entries;

  public ConfigurableEncyclopedia(Map<String, Long> entries) {
      Assert.notNull(entries, "The 'entries' argument cannot be null.");
      this.entries = entries;
  }

  public Long findLong(String entry) {
      return this.entries.get(entry);
  }
}

28.9.Constructor Injection
	28.9.1.	XML Based Bean Configuration: Constructor Injection
	28.9.2.	Constructor Confusion Demo
	28.9.3.	Constructor Caller In Context Config
	28.9.4.	Constructor Argument And Local Reference