Deployment – Spring – Overriding properties when deploying in a multi-server environment

<?xml version="1.0" encoding="UTF-8"?>
<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">
 
    <!--
    This service allows loading of properties based on hostname supporting default values in application.properties and allowing
    other servers to override the default property values in their own server specific application._HOST_NAME_.properties
    -->
    <bean id="applicationProperties" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="systemPropertiesMode" value="1"/>
        <property name="locations">
            <list>
                <value>/WEB-INF/conf/application.properties</value>
                <!--
                    In deployments servers: /WEB-INF/conf/application._HOST_NAME_.properties will override properties in application.properties.
                    based on the hostname in the deployed server
                -->
                <bean class="com.raulraja.util.deployment.CompositeStringResourceProvider" factory-method="getReplacedResource">
                    <constructor-arg>
                        <bean class="com.raulraja.util.deployment.impl.SpringInjectedServletContextProviderImpl" />
                    </constructor-arg>
                    <constructor-arg value="/WEB-INF/conf/application._HOST_NAME_.properties"/>
                </bean>
            </list>
        </property>
        <property name="ignoreResourceNotFound" value="true"/>
    </bean>
 
    <!-- This is a sample service that will get properties injected and will display its values on initialization -->
    <bean id="sampleService" class="com.raulraja.util.deployment.impl.SampleServiceImpl" init-method="init">
        <property name="firstProperty" value="${first.property.placeholder}" />
        <property name="secondProperty" value="${second.property.placeholder}" />
    </bean>
 
</beans>

#In this file live all common properties and default property values for all servers
first.property.placeholder=this value was declared in application.properties
second.property.placeholder=this value was declared in application.properties

# This file contains properties overriden for the host name were the app is being deployed
second.property.placeholder=this value is overriden in a specific server config declared in application.properties

package com.raulraja.util.deployment;
 
import org.apache.log4j.Logger;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ClassPathResource;
import org.springframework.web.context.support.ServletContextResource;
 
import java.net.UnknownHostException;
import java.net.InetAddress;
 
/**
 * A service that provides a resource based on the host name
 */
public class CompositeStringResourceProvider {
 
    private final static Logger log = Logger.getLogger(CompositeStringResourceProvider.class);
 
    private final static String HOSTNAME_PLACEHOLDER = "_HOST_NAME_";
 
	/**
	 * This method is invoked by the container at startup
	 * @param servletContextProvider a servlet context provider
	 * @param baseResource the base resource
	 * @return the resource assigned to the current running server
	 * @throws UnknownHostException if the host is unknown
	 */
    public static Resource getReplacedResource(ServletContextProvider servletContextProvider, String baseResource) throws UnknownHostException {
        InetAddress localhost = InetAddress.getLocalHost();
        baseResource = baseResource.replaceAll(HOSTNAME_PLACEHOLDER, localhost.getHostName());
        Resource resource = null;
        if (servletContextProvider.getServletContext() != null) {
            resource = new ServletContextResource(servletContextProvider.getServletContext(), baseResource);
            if (resource.exists()) {
                log.debug("Loading override for common properties: " + resource.getFilename());
            }
        } else {
            resource = new ClassPathResource(baseResource);
        }
 
        return resource;
    }
 
}

package com.raulraja.util.deployment;
 
import javax.servlet.ServletContext;
 
/**
 * Provides a servlet context
 */
public interface ServletContextProvider {
 
	/**
	 * @return the servlet context
	 */
    ServletContext getServletContext();
 
}

package com.raulraja.util.deployment.impl;
 
 
import com.raulraja.util.deployment.ServletContextProvider;
import org.springframework.web.context.ServletContextAware;
 
import javax.servlet.ServletContext;
 
/**
 * Spring based impl of the ServletContextProvider
 */
public class SpringInjectedServletContextProviderImpl implements ServletContextProvider, ServletContextAware {
 
	/**
	 * the servlet context
	 */
    private ServletContext servletContext;
 
	/**
	 * @return the servlet context
	 */
    public ServletContext getServletContext() {
        return servletContext;
    }
 
	/**
	 * sets the servlet context, invoked by the container at startup since this service implements ServletContextAware 
	 * @param servletContext the servlet context
	 */
    public void setServletContext(ServletContext servletContext) {
        this.servletContext = servletContext;
    }
}

package com.raulraja.util.deployment.impl;
 
import org.apache.log4j.Logger;
 
/**
 * Demonstrates how values of properties are injected based on a specific hostname config
 */
public class SampleServiceImpl {
 
	private final static Logger log = Logger.getLogger(SampleServiceImpl.class);
 
	/**
	 * the first prperty
	 */
	private String firstProperty;
 
	/**
	 * the second property
	 */
	private String secondProperty;
 
	/**
	 * service initialization method
	 */
	public void init() {
		log.debug("first property: " + firstProperty);
		log.debug("second property: " + secondProperty);
	}
 
	/**
	 * sets the first property
	 * @param firstProperty the first property
	 */
	public void setFirstProperty(String firstProperty) {
		this.firstProperty = firstProperty;
	}
 
	/**
	 * sets the second property
	 * @param secondProperty the second property
	 */
	public void setSecondProperty(String secondProperty) {
		this.secondProperty = secondProperty;
	}
}