Spring PropertyPlaceholderConfigurer example

Often times, most Spring developers just put the entire deployment details (database details, log file path) in XML bean configuration file as following :

<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-2.5.xsd">
 
	<bean id="customerDAO" class="com.mkyong.customer.dao.impl.JdbcCustomerDAO">
 
		<property name="dataSource" ref="dataSource" />
	</bean>
 
	<bean id="customerSimpleDAO" class="com.mkyong.customer.dao.impl.SimpleJdbcCustomerDAO">
 
		<property name="dataSource" ref="dataSource" />
	</bean>
 
	<bean id="dataSource"
		class="org.springframework.jdbc.datasource.DriverManagerDataSource">
 
		<property name="driverClassName" value="com.mysql.jdbc.Driver" />
		<property name="url" value="jdbc:mysql://localhost:3306/mkyongjava" />
		<property name="username" value="root" />
		<property name="password" value="password" />
	</bean>
 
</beans>

But, in a corporate environment, deployment detail is usually only can ‘touch’ by your system or database administrator, they just refuse to access your bean configuration file directly, and they will request a separate file for deployment configuration, for example, a simple properties, with deployment detail only.

PropertyPlaceholderConfigurer example

To fix it, you can use PropertyPlaceholderConfigurer class to externalize the deployment details into a properties file, and access from bean configuration file via a special format – ${variable}.

Create a properties file (database.properties), include your database details, put it into your project class path.

	jdbc.driverClassName=com.mysql.jdbc.Driver
	jdbc.url=jdbc:mysql://localhost:3306/mkyongjava
	jdbc.username=root
	jdbc.password=password

Declare a PropertyPlaceholderConfigurer in bean configuration file and map to the ‘database.properties‘ properties file you created just now.

	<bean 
		class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
 
		<property name="location">
			<value>database.properties</value>
		</property>
	</bean>

Full example

<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-2.5.xsd">
 
	<bean
		class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
 
		<property name="location">
			<value>database.properties</value>
		</property>
	</bean>
 
	<bean id="customerDAO" class="com.mkyong.customer.dao.impl.JdbcCustomerDAO">
 
		<property name="dataSource" ref="dataSource" />
	</bean>
 
	<bean id="customerSimpleDAO" 
                class="com.mkyong.customer.dao.impl.SimpleJdbcCustomerDAO">
 
		<property name="dataSource" ref="dataSource" />
	</bean>
 
	<bean id="dataSource"
		class="org.springframework.jdbc.datasource.DriverManagerDataSource">
 
		<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>
 
</beans>
Alternative usage
You also can use PropertyPlaceholderConfigurer to share some constant variables to all other beans. For example, define your log file location in a properties file, and access the properties value from different beans configuration files via ${log.filepath}.

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mkyong
Founder of Mkyong.com and HostingCompass.com, love Java and open source stuff. Follow him on Twitter, or befriend him on Facebook or Google Plus. If you like my tutorials, consider make a donation to these charities.

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