how to read System environment variable in Spring applicationContext

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

Solution 1:

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']}

Solution 2:

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

Solution 3:

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