Working with Set,List,Map and Properties as attributes

We have seen examples of having a classA as one of the attributes of another classB.
We also have cases wherein the attributes of the class are a List of another object(classA).
Example File : Bill

public class Bill {
private List<ABC> abc;
}

File : ABC

Public class ABC{
Private double amount;
Private double discount;
}

For such cases, the value for the List or any other similar collection needs to be injected
through framework, which involves a slight syntactical change.

Step 1 :

Create the POJO which is going to be one of the attributes of another class.  
File : Amount.java

package com.simpleCodeStuffs;
public class Amount {
private double bill;
public double getBill() {
return bill;
}
public void setBill(double bill) {
this.bill = bill;
}
@Override
public String toString(){
return("amount "+bill);
}
}

Step 2 :

CollectionBean is a class, which has a list,set,map,properties of another Object as its attributes. Just to enhance the understanding, we take it that CollectionBean may have a List of any Object as its attributes. Hence the attributes are defined as List of Object and likewise.

File : CollectionBean.java

package com.simpleCodeStuffs;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
public class CollectionBean {
        private List<String> stringListVariable;
        private List<Object> listVariable;
        private Set<Object> setVariable;
        private Map<Object, Object> mapVariable;
        private Properties propVariable;
        
        
        public List<String> getStringListVariable() {
                return stringListVariable;
        }
    public void setStringListVariable(List<String> stringListVariable) {
                this.stringListVariable = stringListVariable;
        }
        public List<Object> getListVariable() {
                return listVariable;
        }
        public void setListVariable(List<Object> listVariable) {
                this.listVariable = listVariable;
        }
        public Set<Object> getSetVariable() {
                return setVariable;
        }
        public void setSetVariable(Set<Object> setVariable) {
                this.setVariable = setVariable;
        }
        public Map<Object, Object> getMapVariable() {
                return mapVariable;
        }
      public void setMapVariable(Map<Object, Object> mapVariable) {
                this.mapVariable = mapVariable;
        }
        public Properties getPropVariable() {
                return propVariable;
        }
       public void setPropVariable(Properties propVariable) {
                this.propVariable = propVariable;
        }
}

Step 3 : Main class to print the details of the attributes

File : MainClass.java

package com.simpleCodeStuffs;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.simpleCodeStuffs.Amount;
import com.simpleCodeStuffs.CollectionBean;
public class MainClass {
         public static void main(String[] args) { 

            ApplicationContext context = 

           new ClassPathXmlApplicationContext("Beans.xml")

         CollectionBean bean=(CollectionBean)context.getBean("testBean");
         Amount amt=(Amount)context.getBean("amount"); 

      System.out.println("List of String:t"+bean.getStringListVariable()); 

         System.out.println("List          :t"+bean.getListVariable());
         System.out.println("set           :t"+bean.getSetVariable();

         System.out.println("Map           :t"+bean.getMapVariable());
         System.out.println("Properties    :t"+bean.getPropVariable());
           }
}

Step 4 :

This is the main change. For each of the collection variables, the way in which the value is injected in the configuration metadata has a syntax change.

‘list’, ‘set’,’map’,’props’ tags are used respectively for List, Set, Map and Properties collections

File : Beans.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" 

   xsi:schemaLocation="http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

      <bean id="testBean" class="com.simpleCodeStuffs.CollectionBean">
                <property name="stringListVariable">
                        <list>
                                <value>A Simple</value>
                                <value>List</value>
                                <value>Of</value>
                                <value>String</value>
                        </list>
                </property>
                <property name="listVariable">
                        <list>
                                <value>1</value>
                                <value>List of Objects</value>
                                <ref bean="amount" />
                                <bean class="com.simpleCodeStuffs.Amount">
                                  <property name="bill">
                                               <value>45.9</value>
                                      </property>
                                </bean>
                        </list>
                </property>
                <property name="setVariable">
                        <set>
                                <value>2</value>
                                <value>Set of Objects</value>
                                <ref bean="amount" />
                                <bean class="com.simpleCodeStuffs.Amount" 

                             <property name="bill">
                                  <value>09.5</value>
                                        </property>
                                </bean>
                        </set>
                </property>
                <property name="mapVariable">
                        <map>
                                <entry key="a" value="3" />
                                <entry key="b" value="Map of Objects" />
                                <entry key="c" value-ref="amount" />
                                <entry key="d" 

                        <bean class="com.simpleCodeStuffs.Amount"> 

                                 <property name="bill">
                                    <value>76.5</value>
                                      </property>
                                        </bean>
                                </entry>
                        </map>
                </property>
                <property name="propVariable">
                        <props>
                            <prop key="a">4</prop>
                            <prop key="b">properties</prop>
                      </props>
                </property>
        </bean>

      <bean id="amount" class="com.simpleCodeStuffs.Amount">
                <property name="bill">
                        <value>56.9</value>
                </property>
        </bean>
</beans>

Injection of any variable of any kind viz., primitive data type, reference to another bean, inner bean can be done for the above Collections as shown

The first example shown, “stringListVariable” is simply to state the means by which multiple values of a simple Data type can be injected into the list. The other variables take values of type Object. Hence, first an Integer, then a String is inserted.
The third one is to show how a reference to another bean can be inserted as a value to the list/set/map. The fourth one shows how an inner bean can be defined and the value inserted to the list/set/map. Note here that, while defining an inner bean, there is no need to mention the beanId as it has limited scope to only the outer bean which defines it.