How to add Properties to an Application Context

Question

I have a Standalone Application, this application calculates a value (Property) and then starts a Spring Context. My question is how can I add that calculated property to th

Answer 1

In Spring 3.1 you can implement your own PropertySource, see: Spring 3.1 M1: Unified Property Management.

First, create your own PropertySource implementation:

private static class CustomPropertySource extends PropertySource<String> {

    public CustomPropertySource() {super("custom");}

    @Override
    public String getProperty(String name) {
        if (name.equals("myCalculatedProperty")) {
            return magicFunction();  //you might cache it at will
        }
        return null;
    }
}

Now add this PropertySource before refreshing the application context:

AbstractApplicationContext appContext =
    new ClassPathXmlApplicationContext(
        new String[] {"applicationContext.xml"}, false
    );
appContext.getEnvironment().getPropertySources().addLast(
   new CustomPropertySource()
);
appContext.refresh();

From now on you can reference your new property in Spring:

<context:property-placeholder/>

<bean class="com.example.Process">
    <constructor-arg value="${myCalculatedProperty}"/>
</bean>

Also works with annotations (remember to add <context:annotation-config/>):

@Value("${myCalculatedProperty}")
private String magic;

@PostConstruct
public void init() {
    System.out.println("Magic: " + magic);
}

Answer 2

If You are controlling the creation of ApplicationContext as in Your example than You can always add a BeanRegistryPostProcessor to add a second PropertyPlaceholderConfigurer into the context. It should have ignoreUnresolvablePlaceholders="true" and order="1" and resolve only the custom calculated properties using the Properties object. All other properties should be resolved by the PropertyPlaceholderConfigurer from the XML that should have order="2".

Answer 3

Your myCalculatedProperty must be contained within one of your properties file (which are injected by the Spring propertyPlaceholderConfigurer).

EDIT : simply use the setter, something like this

public static void main(final String[] args) {
    String myCalculatedProperty = magicFunction();         
    AbstractApplicationContext appContext =
          new ClassPathXmlApplicationContext("applicationContext.xml");

    Process p = appContext.getBean(Process.class);
    p.setMyCalculatedProperty(myCalculatedProperty);
    p.start();
}

Answer 4

You can add the calculated value to the system properties:

System.setProperty("placeHolderName", myCalculatedProperty);