Spring Framework Setter Injection with Examples

In this tutorial we will discuss Spring Framework Setter Injection which is the main method of dependency injection in Spring. In the previous tutorial we discussed constructor injection, which is the another method. The property element is used to define the setter injection in Spring by using the name of the property element and looking for the corresponding setXXXXXX methods in the specified bean. The following table will provide a guideline for how Spring maps property names to Java setter method names.

Setter Injection Naming Conventions

Property Name	Setter Method Name
name	setName()
email	setEmail()
favoriteName	setFavoriteName()
HTML	setHTML()

Setter Injection – Populating Basic Elements

Populating a bean is quite easy in Spring. Using the property element we are able to assign any of the properties of the bean by using the name attribute. When we do so, Spring will call the appropriate setter method that matches using the naming conventions described above. It will then assign the value of the field found in the value attribute.

<bean id="client" class="com.avaldes.Client">
  <property name="id" value="123"></property>
  <property name="name" value="Amaury Valdes"></property>
  <property name="email" value="amaury@mail.com"></property>
  <property name="active" value="true"></property>
  <!-- more -->
</bean>

Reference Injection

In reference injection, values are injected by reference. The definitions from one bean are injected into another. To do this, instead of using the attribute value, you use the ref attribute and refer to the bean’s id of the other.

  <bean id="company" class="com.avaldes.Company">
    <property name="name" value="TasteOHoney"></property>
    <property name="numEmployees" value="10"></property>  
    <property name="client" ref="clientBean"></property>
  </bean>
  
  <bean id="clientBean" class="com.avaldes.Client">
    <property name="id" value="123"></property>
    <property name="name" value="Amaury Valdes"></property>
    <!-- more -->
  </bean>

Setter Injection – Populating List Collection Elements

For the List collection, we use the property element with name attribute of “children“, create the list node and add value nodes with each of Albert Einstein’s children.

<property name="children">
  <list>
    <value>Hans Albert Einstein</value>
    <value>Eduardo Einstein</value>
  </list>
</property>

Setter Injection – Populating Map Collection Elements

Next, we will work on Map collection, which has key/value pairs. In this example, the collection is aptly named “phones“. We create the Map node, but will need to add entry key nodes with each key correctly labeled and the value for each phone in the corresponding value node.

<property name="phones">
  <map>
    <entry key="home">
      <value>212-555-1212</value>
    </entry>
    <entry key="mobile">
      <value>212-444-1313</value>
    </entry>
    <entry key="work">
      <value>212-333-3456</value>
    </entry>
  </map>
</property>

Setter Injection – Populating Set Collection Elements

In this last example, we are populating a Set which looks very similar to List, except that the node will correspond to set instead of list. The main differing quality between a Set and List is that sets do not contain duplicate elements.

<property name="favoriteNumbers">
  <set>
    <value>11</value>
    <value>17</value>
    <value>25</value>
    <value>39</value>
  </set>
</property>

Application Context (spring-config.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:p="http://www.springframework.org/schema/p"
  xsi:schemaLocation="
    http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans.xsd">
 
  <bean id="companyBean" class="com.avaldes.Company">
    <property name="name" value="TasteOHoney"></property>
    <property name="numEmployees" value="10"></property>  
    <property name="client" ref="clientBean"></property>
  </bean>
  
  <bean id="clientBean" class="com.avaldes.Client">
    <property name="id" value="123"></property>
    <property name="name" value="Amaury Valdes"></property>
    <property name="email" value="amaury@mail.com"></property>
    <property name="active" value="true"></property>
    <property name="children">
      <list>
      <value>Hans Albert Einstein</value>
      <value>Eduardo Einstein</value>
      </list>
    </property>
    <property name="phones">
      <map>
        <entry key="home">
          <value>212-555-1212</value>
        </entry>
        <entry key="mobile">
          <value>212-444-1313</value>
        </entry>
        <entry key="work">
          <value>212-333-3456</value>
        </entry>
      </map>
    </property>
    <property name="favoriteNumbers">
      <set>
      <value>11</value>
      <value>17</value>
      <value>25</value>
      <value>39</value>
      </set>
    </property>
  </bean>
  
</beans>

Maven Project Object Model (pom.xml)

<project xmlns="http://maven.apache.org/POM/4.0.0" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
   http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>
  <groupId>org.springframework.samples</groupId>
  <artifactId>SpringSetterInjectionExample</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  
  <properties>
  <!-- Generic properties -->
  <java.version>1.6</java.version>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
  </properties>
  
  <dependencies>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>3.1.1.RELEASE</version>
  </dependency>
  </dependencies> 
</project>

Company Class (Company.java)

package com.avaldes;

public class Company {
  private String name;
  private int numEmployees;
  private Client client;
  
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public int getNumEmployees() {
    return numEmployees;
  }
  public void setNumEmployees(int numEmployees) {
    this.numEmployees = numEmployees;
  }
  public Client getClient() {
    return client;
  }
  public void setClient(Client client) {
    this.client = client;
  }
  
  @Override
  public String toString() {
    return "Company [name=" + name + ", numEmployees=" + numEmployees
        + ", client=" + client + "]";
  }
}

Client Class (Client.java)

package com.avaldes;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;

public class Client {
  private int id;
  private String name;
  private String email;
  private boolean active;
  private ArrayList<String> children;
  private HashMap<String, String> phones;
  private HashSet<Integer> favoriteNumbers; 
  
  public int getId() {
    return id;
  }

  public void setId(int id) {
    this.id = id;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public String getEmail() {
    return email;
  }

  public void setEmail(String email) {
    this.email = email;
  }

  public boolean isActive() {
    return active;
  }

  public void setActive(boolean active) {
    this.active = active;
  }

  public ArrayList<String> getChildren() {
    return children;
  }

  public void setChildren(ArrayList<String> children) {
    this.children = children;
  }

  public HashMap<String, String> getPhones() {
    return phones;
  }

  public void setPhones(HashMap<String, String> phones) {
    this.phones = phones;
  }

  public HashSet<Integer> getFavoriteNumbers() {
    return favoriteNumbers;
  }

  public void setFavoriteNumbers(HashSet<Integer> favoriteNumbers) {
    this.favoriteNumbers = favoriteNumbers;
  }

  public Client() {
    System.out.println("Inside Client() constructor...");
  }

  @Override
  public String toString() {
    return "Client [id=" + id + ", name=" + name + ", email=" + email
        + ", active=" + active + ", children=" + children + ", phones="
        + phones + ", favoriteNumbers=" + favoriteNumbers + "]";
  }
}

Tester Application (TestSetterInjection.java)

This simple tester application simply gets the spring configuration metadata from the spring-config.xml. Gets the bean called companyBean from the beanFactory and displays its contents to the console by using the toString() method.

package com.avaldes;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestSetterInjection {

  public static void main(String[] args) {
    BeanFactory beanFactory = 
         new ClassPathXmlApplicationContext("spring-config.xml");
    Company company = (Company) beanFactory.getBean("companyBean");
    System.out.println("Output: " + company.toString());
  }
}

Output – Setter Injection (DI)

Output: Company [name=TasteOHoney, numEmployees=10, client=Client [id=123, name=Amaury Valdes, email=amaury@mail.com, active=true, children=[Hans Albert Einstein, Eduardo Einstein], phones={home=212-555-1212, mobile=212-444-1313, work=212-333-3456}, favoriteNumbers=[11, 17, 25, 39]]]

That’s It

Enjoy Spring Framework!

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