Spring Dependency Injection - An Introductory Tutorial

Using property place holder configurer

Let's say for each installation of an ATM, the installer may need to configure the number of retries. You probably don't want the installer messing with your XML file for your application context because it is too much like code and too many things could go wrong. Instead, perhaps you could just edit a properties file. The properties file could have properties for each of the things that may vary for a given installation of an AutomatedTellerMachineImpl.

atm.properties Properties file

transport.retries=8

applicationContext.xml using property-placeholder tag

<?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"
        xmlns:p="http://www.springframework.org/schema/p" 
        xsi:schemaLocation="
                http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
                http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">
        
        <context:property-placeholder location="classpath:atm.properties"   />
        
        
        <bean id="soapTransport" class="com.arcmind.springquickstart.SoapAtmTransport" p:retries="${transport.retries}"/>
        
        <bean id="atm" class="com.arcmind.springquickstart.AutomatedTellerMachineImpl">
                <constructor-arg index="0" ref="soapTransport" />
        </bean>

</beans>

Notice the property-placeholder loads the atm.properties file from the classpath. Then you use the transport.retries defined in the atm.properties file as follows: p:retries="${transport.retries}".
Figure 9 illustrates using the property placeholder configurer. 

You could load properties file from the file system using file: instead of classpath: in the location as follows:

Loading the properties file from the file system with the property-placeholder

        <context:property-placeholder location="file:./src/main/resources/atm.properties"   />
        
        
        <bean id="soapTransport" class="com.arcmind.springquickstart.SoapAtmTransport" p:retries="${transport.retries}"/>
        
        <bean id="atm" class="com.arcmind.springquickstart.AutomatedTellerMachineImpl">
                <constructor-arg index="0" ref="soapTransport" />
        </bean>

Rick Hightower is CTO of Mammatus and is an expert on Java and Cloud Computing. Rick is invovled in Java CDI advocacy and Java EE. CDI Implementations - Resin Candi - Seam Weld - Apache OpenWebBeans