Dónal Dónal - 1 month ago 13
Java Question

How can I inject a property value into a Spring Bean which was configured using annotations?

I have a bunch of Spring beans which are picked up from the classpath via annotations, e.g.

@Repository("personDao")
public class PersonDaoImpl extends AbstractDaoImpl implements PersonDao {
// Implementation omitted
}


In the Spring XML file, there's a PropertyPlaceholderConfigurer defined:

<bean id="propertyConfigurer"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="location" value="/WEB-INF/app.properties" />
</bean>


I want to inject one of the properties from app.properites into the bean shown above. I can't simply do something like

<bean class="com.example.PersonDaoImpl">
<property name="maxResults" value="${results.max}"/>
</bean>


Because PersonDaoImpl does not feature in the Spring XML file (it is picked up from the classpath via annotations). I've got as far as the following:

@Repository("personDao")
public class PersonDaoImpl extends AbstractDaoImpl implements PersonDao {

@Resource(name = "propertyConfigurer")
protected void setProperties(PropertyPlaceholderConfigurer ppc) {
// Now how do I access results.max?
}
}


But it's not clear to me how I access the property I'm interested in from
ppc
?

Answer

You can do this in Spring 3 using EL support. Example:

@Value("#{systemProperties.databaseName}")
public void setDatabaseName(String dbName) { ... }

@Value("#{strategyBean.databaseKeyGenerator}")
public void setKeyGenerator(KeyGenerator kg) { ... }

systemProperties is an implicit object and strategyBean is a bean name.

One more example, which works when you want to grab a property from a Properties object. It also shows that you can apply @Value to fields:

@Value("#{myProperties['github.oauth.clientId']}")
private String githubOauthClientId;

Here is a blog post I wrote about this for a little more info.

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