Externalizing properties with PropertyPlaceholderConfigurer

PropertyPlaceholderConfigurer is another convenient utility to externalize property values from a bean definition into a separate file that uses the standard java.util.Properties format. It replaces placeholders in XML bean definitions with matching property values in the configured property file, as shown here. This is the best way to externalize profile or environment-specific information such as datasource config, e-mail settings, and so on. The DevOps team will just edit these property files and never mess with your code:

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations" value="classpath:datasource.properties"/>
</bean>

<bean id="dataSource" destroy-method="close"
        class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="${jdbc.driverClassName}"/>
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>

Here is another simpler declaration of PropertyPlaceholder:

<context:property-placeholder location="classpath:datasource.properties"/>