[Spring]: XML Configuration

spring

09/10/2019

Methods to create a spring container

Full XML Config
Java Annotation
Java Configuration Class (No XML needed)

xml configuration (and IoC)

There are three differnet ways to create/configure Spring container. This is a first method to create with xml configuration file. Link to IoC

Main method

JAVA

public static void main(String args[]) {
    // load spring config file (create spring container)
    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("fileName.xml");

    // retrieve bean from spring container
    Player player = context.getBean("myPlayer", Player.class);

    // Call methods on the bean
    System.out.println(player.getWorkout());
    System.out.println(player.getFortune());

    // close the context
    context.close();
}

make sure that xml file is located in src directory

XML file

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

    <!-- Creating an object -->
    <bean id="myPlayer" class="com.ellismin.BasketballPlayer">
    </bean>

</beans>

Explanation

JAVA

Player player = context.getBean("myPlayer", Player.class);

XML

<bean id="myPlayer" class="com.ellismin.BasketballPlayer">
</bean>

Retrives the bean from xml config file. This grabs the bean object with name myPlayer
Without the use of IoC, above codes would look like:

JAVA

Player myPlayer = new BasketballPlayer();

Player.class in parameter is required because when Spring pass the interface to the method behind the scenes, Spring will cast the object for you
com.ellismin.BasketballPlayer is a fully qualified name; packageName.className

Dependency Injection

Spring allows you to inject dependency(helper) from xml config
Code below includes examples of constructor injection, setter injection

XML

<?xml version=1.0 encoding="UTF-8"?>
<beans...>
    <!-- Create dependency(helper) object -->
    <bean id="myWeather" class="com.ellismin.SunnyWeather"></bean>

    <bean id="myPlayer" class="com.ellismin.BasketballPlayer">

        <!-- Constructor injection -->
        <constructor-arg ref="myWeather" />

        <!-- Setter injection -->
        <property name="weather" ref="myWeather"/>

        <!-- Setter injection w/ literal value -->
        <property name="email" value="[email protected]"/>

        <!-- Setter injection from properties file -->
        <property name="email" value="${john.email}" />

    </bean>
</beans...>

How interfaces & classes look like

JAVA

public interface Player {
    public String getWorkout();
    public String getWeather();
}

JAVA

public class BasketballPlayer implements Player {
    private Weather weather;
    private String email;

    public BasketballPlayer(Weather weather) {
        this.weather = weather
    }
    @Override
    public String getWorkout() {
        return "playing basketball";
    }
    @Override
    public String getWeather() {
        return weather.getWeather();
    }
    // Setter injection example
    public void setWeather(Weather weather) {
        this.weather = weather;
    }
    // Setter injection example w/ literal value OR properties file
    public void setEmail(String email) {
        this.email = email;
    }

}

JAVA

public interface Weather {
    public String getWeather();
}

JAVA

public class SunnyWeather implements Weather {
    @Override
    public String getWeather() {
        return "Today will be sunny all day!"
    }
}

Explanation

XML

<bean id="myWeather" class="com.ellismin.SunnyWeather"></bean>

This creates the dependency (helper) object that will be used as parameter for BasketballPlayer class
Above would look like:

JAVA

SunnyWeather weather = new SunnyWeather();

XML

<bean id="myPlayer" class="com.ellismin.BasketballPlayer">
</bean>

This code piece would be equivalent to:

JAVA

Player myPlayer = new BasketballPlayer();

XML

<bean id="myPlayer" class="com.ellismin.BasketballPlayer">
        <!-- Constructor injection -->
        <constructor-arg ref="myWeather" />
    </bean>

With constructor injection:

JAVA

Player myPlayer = new BasketballPlayer(weather);

Setting literal value & value from properties file

XML

<bean id="myPlayer" class="com.ellismin.BasketballPlayer">
        <!-- Setter injection -->
        <property name="weather" ref="myWeather"/>
        <!-- Setter injection w/ literal value -->
        <property name="email" value="[email protected]"/>
        <!-- Setter injection from properties file -->
        <property name="email" value="${john.email}" />

    </bean>

With setter injection:
1. property name weather will look for a setter method setWeather and pass in the reference weather.
2. similarly, property name email will look for setEmail method and pass in the literal value or value from file
To inject value from properties file, xml needs extra code to scan the file

XML

<?xml version=1.0 encoding="UTF-8"?>
<beans...>
<!-- Load properties file: emailList.properties -->
    <context:property-placeholder
        location="classpath:emailList.properties" />
</beans...>

emailList.properties would look like:

BASH

ellis.email=[email protected]
john.email=[email protected]

In the above example, \${john.email} will grab [email protected] from file then pass it into setEmail method as parameter
The program outputs:

BASH

playing basketball
Today will be sunny all day!

Scope for xml

XML

<beans...>
  <bean id="myPlayer" class="com.ellismin" scope="singleton">
  ...
</beans...>

Singleton is set by default. We can chance it to prototype for desired usage

Init / Destroy

Init and Destroy methods can be accomplished with added methods in java along with method names in xml file

XML

<beans...>
  <bean id="myPlayer" class="com.ellismin" init-method="doStartUp" destroy-method="doCleanUp">
  ...
</beans...>

JAVA

public class BasketballPlayer implements Player {
    ...
    // Init method
    public void doStartUp() {
        System.out.println("Start up");
    }
    // Destroy method
    public void doCleanUp() {
        System.out.println("cleanUp");
    }
}

Note: For prototype scoped beans, SPring does not call the destroy method!
- Spring doesn't manage the complete lifecycle of a prototype bean

WRITTEN BY

Ellis Min

Keeping a record

GitHub