Read Property Files in Spring

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In this short article, we will discuss different ways to read property files in Spring-based web applications.

Reading Files using Bean Namespace

Below example shows reading properties from a file. We use PropertyPlaceholderConfigurer bean and it's location property used to load property files. Here is how properties can be read from a file using the bean namespace:
<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.xsd">
    <!-- reading the properties, Spring infrastructure bean is exposed -->
    <bean
 class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations" value="classpath:db/datasource.properties"/>
    </bean>
    <!-- here the values are injected into a datasource -->
    <bean id="dataSource1"
 class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="${driverClassName}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
    </bean>
</beans>

Reading Files using Context Namespace

Here is how properties can be read from a file using the context namespace:
<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">
    <!-- Spring infrastructure is not visible anymore -->
    <context:property-placeholder location="classpath:db/datasource.properties" />
    <!-- here the values are injected into a datasource -->
    <bean id="dataSource2"
 class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="${driverClassName}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
    </bean>
</beans>

Reading Files using Util Namespace

Here is how properties can be read from a file using the util namespace:
<?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:util="http://www.springframework.org/schema/util"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans.xsd
 http://www.springframework.org/schema/util
 http://www.springframework.org/schema/util/spring-util.xsd">
    <!-- Spring infrastructure is not visible anymore -->
    <util:properties id="dbProp" location="classpath:db/datasource.properties"/>
    <bean id="dataSource3"
 class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="#{dbProp.driverClassName}"/>
        <property name="url" value="#{dbProp.url}"/>
        <property name="username" value="#{dbProp.username}"/>
        <property name="password" value="#{dbProp.password}"/>
    </bean>
</beans>

Reading Files using Spring Java-based Configuration - @PropertySource annotation

The @PropertySource annotation to externalize your configuration to a properties file.
In this example, we are reading database configuration from config.properties file and set these property values to DataSourceConfig class using Environment.
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;

@Configuration
@PropertySource("classpath:config.properties")
public class ProperySourceDemo implements InitializingBean {

    @Autowired
    Environment env;

    @Override
    public void afterPropertiesSet() throws Exception {
        setDatabaseConfig();
    }

    private void setDatabaseConfig() {
        DataSourceConfig config = new DataSourceConfig();
        config.setDriver(env.getProperty("jdbc.driver"));
        config.setUrl(env.getProperty("jdbc.url"));
        config.setUsername(env.getProperty("jdbc.username"));
        config.setPassword(env.getProperty("jdbc.password"));
        System.out.println(config.toString());
    }
}

Spring @PropertySource Annotation Placeholders Example

Any ${…} placeholders present in a @PropertySource resource location will be resolved against the set of property sources already registered against the environment. 
For example:
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;

@Configuration
@PropertySource("classpath:/com/${my.placeholder:default/path}/config.properties")
public class ProperySourceDemo implements InitializingBean {

    @Autowired
    Environment env;

    @Override
    public void afterPropertiesSet() throws Exception {
        setDatabaseConfig();
    }

    private void setDatabaseConfig() {
        DataSourceConfig config = new DataSourceConfig();
        config.setDriver(env.getProperty("jdbc.driver"));
        config.setUrl(env.getProperty("jdbc.url"));
        config.setUsername(env.getProperty("jdbc.username"));
        config.setPassword(env.getProperty("jdbc.password"));
        System.out.println(config.toString());
    }
}

Reading Multiple Property Files using @PropertySources Annotation

Introduces new @PropertySources to support Java 8 and a better way to include multiple properties files.
 @Configuration
 @PropertySources({
  @PropertySource("classpath:config.properties"),
  @PropertySource("classpath:db.properties")
 })
 public class AppConfig {
  //...
 }
Allow @PropertySource to ignore the not found properties file.
 @Configuration
 @PropertySource("classpath:missing.properties")
 public class AppConfig {
  //...
 }
If missing.properties is not found, the system is unable to start and throws FileNotFoundException
 Caused by: java.io.FileNotFoundException: 
  classpath resource [missiong.properties] cannot be opened because it does not exist
In Spring 4, you can use ignoreResourceNotFound to ignore the not found properties file
 @Configuration
 @PropertySource(value="classpath:missing.properties", ignoreResourceNotFound=true)
 public class AppConfig {
  //...
 }

        @PropertySources({
        @PropertySource(value = "classpath:missing.properties", ignoreResourceNotFound=true),
        @PropertySource("classpath:config.properties")
        })

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