how to read System environment variable in Spring

Question

How to read the system environment variable in the application context?

I want something like :

<util:properties id="dbProperties"
        location="classpath:config_DEV/db.properties" />

or

<util:properties id="dbProperties"
        location="classpath:config_QA/db.properties" />

depending on the environement.

Can I have something like this in my application Context?

<util:properties id="dbProperties"
        location="classpath:config_${systemProperties.env}/db.properties" />

where the actual val is set based on the SYSTEM ENVIRONMENT VARIABLE

I'm using Spring 3.0

Answer 1

Nowadays you can put

@Autowired
private Environment environment;

in your @Component, @Bean, etc., and then access the properties through the Environment class:

environment.getProperty("myProp");

---

For a single property in a @Bean

@Value("${my.another.property:123}") // value after ':' is the default
Integer property;

---

Another way are the handy @ConfigurationProperties beans:

@ConfigurationProperties(prefix="my.properties.prefix")
public class MyProperties {
  // value from my.properties.prefix.myProperty will be bound to this variable
  String myProperty;

  // and this will even throw a startup exception if the property is not found
  @javax.validation.constraints.NotNull
  String myRequiredProperty;

  //getters
}

@Component
public class MyOtherBean {
  @Autowired
  MyProperties myProperties;
}

Note: Just remember to restart eclipse after setting a new environment variable

Answer 2

Thanks to @Yiling. That was a hint.

<bean id="propertyConfigurer"
        class="org.springframework.web.context.support.ServletContextPropertyPlaceholderConfigurer">

    <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />
    <property name="searchSystemEnvironment" value="true" />
    <property name="locations">
        <list>
            <value>file:#{systemEnvironment['FILE_PATH']}/first.properties</value>
            <value>file:#{systemEnvironment['FILE_PATH']}/second.properties</value>
            <value>file:#{systemEnvironment['FILE_PATH']}/third.properties</value>
        </list>
    </property>
</bean>

After this, you should have one environment variable named 'FILE_PATH'. Make sure you restart your machine after creating that environment variable.

Answer 3

For my use case, I needed to access just the system properties, but provide default values in case they are undefined.

This is how you do it:

<bean id="propertyPlaceholderConfigurer"   
    class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">  
    <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />
    <property name="searchSystemEnvironment" value="true" />
</bean>  
<bean id="myBean" class="path.to.my.BeanClass">
    <!-- can be overridden with -Dtest.target.host=http://whatever.com -->
    <constructor-arg value="${test.target.host:http://localhost:18888}"/>
</bean>

Answer 4

Check this article. It gives you several ways to do this, via the PropertyPlaceholderConfigurer which supports external properties (via the systemPropertiesMode property).

Answer 5

You are close :o) Spring 3.0 adds Spring Expression Language. You can use

<util:properties id="dbProperties" 
    location="classpath:config_#{systemProperties['env']}/db.properties" />

Combined with java ... -Denv=QA should solve your problem.

Note also a comment by @yiling:

In order to access system environment variable, that is OS level variables as amoe commented, we can simply use "systemEnvironment" instead of "systemProperties" in that EL. Like #{systemEnvironment['ENV_VARIABLE_NAME']}

Answer 6

You can mention your variable attributes in a property file and define environment specific property files like local.properties, production.propertied etc.

Now based on the environment, one of these property file can be read in one the listeners invoked at startup, like the ServletContextListener.

The property file will contain the the environment specific values for various keys.

Sample "local.propeties"

db.logsDataSource.url=jdbc:mysql://localhost:3306/logs
db.logsDataSource.username=root
db.logsDataSource.password=root

db.dataSource.url=jdbc:mysql://localhost:3306/main
db.dataSource.username=root
db.dataSource.password=root

Sample "production.properties"

db.logsDataSource.url=jdbc:mariadb://111.111.111.111:3306/logs
db.logsDataSource.username=admin
db.logsDataSource.password=xyzqer

db.dataSource.url=jdbc:mysql://111.111.111.111:3306/carsinfo
db.dataSource.username=admin
db.dataSource.password=safasf@mn

For using these properties file, you can make use of REsource as mentioned below

        PropertyPlaceholderConfigurer configurer = new PropertyPlaceholderConfigurer();
        ResourceLoader resourceLoader = new DefaultResourceLoader();

        Resource resource = resourceLoader.getResource("classpath:"+System.getenv("SERVER_TYPE")+"DB.properties");
        configurer.setLocation(resource);
        configurer.postProcessBeanFactory(beanFactory);

SERVER_TYPE can be defined as the environment variable with appropriate values for local and production environment.

With these changes the appplicationContext.xml will have the following changes

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
 <property name="driverClassName" value="com.mysql.jdbc.Driver" />
  <property name="url" value="${db.dataSource.url}" />
  <property name="username" value="${db.dataSource.username}" />
  <property name="password" value="${db.dataSource.password}" />

Hope this helps .