how to read System environment variable in Spring applicationContext

Question

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']}

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

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

Yes, you can do <property name="defaultLocale" value="#{ systemProperties['user.region']}"/> for instance.

The variable systemProperties is predefined, see 6.4.1 XML based configuration.

In your bean definition, make sure to include "searchSystemEnvironment" and set it to "true". And if you're using it to build a path to a file, specify it as a file:/// url.

So for example, if you have a config file located in

/testapp/config/my.app.config.properties

then set an environment variable like so:

MY_ENV_VAR_PATH=/testapp/config

and your app can load the file using a bean definition like this:

e.g.

<bean class="org.springframework.web.context.support.ServletContextPropertyPlaceholderConfigurer">
    <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" />
    <property name="searchSystemEnvironment" value="true" />
    <property name="searchContextAttributes" value="true" />
    <property name="contextOverride" value="true" />
    <property name="ignoreResourceNotFound" value="true" />
    <property name="locations">
        <list>
            <value>file:///${MY_ENV_VAR_PATH}/my.app.config.properties</value>
        </list>
    </property>
</bean>

Using Spring EL you can eis example write as follows

<bean id="myBean" class="path.to.my.BeanClass">
    <!-- can be overridden with -Dtest.target.host=http://whatever.com -->
    <constructor-arg value="#{systemProperties['test.target.host'] ?: 'http://localhost:18888'}"/>
</bean>