Often times, most Spring developers just put the deployment details (database details, log file path) in the 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>

In a corporate environment, the deployment detail is usually only can ‘touch’ by your system or database administrator, they just refuse to access your bean configuration file instead of request a new separate file for the deployment configuration.

In Spring, 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}.

Example

Create a properties file (database.properties) and include your deployment 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 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}.

You can download this example here – Spring-JDBC-PropertyPlaceholderConfigurer-Example.zip

This article was posted in Spring category.

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