How to Inject Property Values into Spring Beans Configured via Annotations?

Property Injection for Spring Beans Configured via Annotations

Spring beans detected via annotations present a challenge when it comes to injecting property values. While the PropertyPlaceholderConfigurer can load properties from an external file, simply setting a bean property's value in the XML configuration won't work for these beans.

To address this, Spring 3 introduced EL support, allowing values to be injected dynamically. In particular:

Injected Value with EL Expressions

@Value("#{.} allows directly injecting the value of a property from an implicit object.
@Value("#{.} also enables injecting a property from the specified bean.
For instance, to inject the "results.max" property from an external properties file:

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

    @Resource(name = "propertyConfigurer")
    protected void setProperties(PropertyPlaceholderConfigurer ppc) {
        maxResults = ppc.getProperties().getProperty("results.max"); 
    }
}

EL also provides more complex options for manipulating values, retrieving bean references, and resolving placeholders.

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