How to @Inject Property File Properties With CDI
Learn how to @inject Property files for your Java app with CDI in this neat tutorial, with annotations, producers, and more!
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You use CDI for your Java application and want to use a Property file for some needed configuration, but don't know how to do this...
Solution
Create @Producer(s) and an annotation to direct it.
Annotation
package nl.ivonet.config;
import javax.enterprise.util.Nonbinding;
import javax.inject.Qualifier;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
/**
* Represents an property key to be injected
*/
RUNTIME) (
TYPE, METHOD, FIELD, PARAMETER}) ({
public @interface Property {
String value() default "";
boolean required() default true;
}
Producer
The examples provided here enable parsing of Strings, Booleans and Integers but you can, of course, add producers as needed. Note that the getKey method first looks if the @Property annotation has a value and if so it will take that as the key for the property file, but if you don't provide a value it will take the annotated field name as the key.
package nl.ivonet.config;
import javax.annotation.PostConstruct;
import javax.enterprise.inject.Produces;
import javax.enterprise.inject.spi.InjectionPoint;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
public class PropertyProducer {
private Properties properties;
public String produceString(final InjectionPoint ip) {
return this.properties.getProperty(getKey(ip));
}
public int produceInt(final InjectionPoint ip) {
return Integer.valueOf(this.properties.getProperty(getKey(ip)));
}
public boolean produceBoolean(final InjectionPoint ip) {
return Boolean.valueOf(this.properties.getProperty(getKey(ip)));
}
private String getKey(final InjectionPoint ip) {
return (ip.getAnnotated()
.isAnnotationPresent(Property.class) &&
!ip.getAnnotated()
.getAnnotation(Property.class)
value().isEmpty()) ? ip.getAnnotated()
.getAnnotation(Property.class)
.value()
: ip.getMember()
.getName();
}
public void init() {
this.properties = new Properties();
final InputStream stream = PropertyProducer.class
.getResourceAsStream("/application.properties");
if (stream == null) {
throw new RuntimeException("No properties!!!");
}
try {
this.properties.load(stream);
} catch (final IOException e) {
throw new RuntimeException("Configuration could not be loaded!");
}
}
}
Usage
private String rootFolder;
or
"root.folder.key.here") (
private String rootFolder;
application.properties
rootFolder=/helloWorldFolder
root.folder.key.here=/another/folder/name
Extra Consideration
Note that when using this method for injecting Strings and stuff it might get difficult to write Unit tests as Mocking frameworks cannot Mock final classes (e.g. String). If you get to this problem you might want to look at this article.
Have fun,
Ivo.
Published at DZone with permission of Ivo Woltring. See the original article here.
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