Over a million developers have joined DZone.
{{announcement.body}}
{{announcement.title}}

How to @Inject Property File Properties With CDI

DZone's Guide to

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!

· Java Zone ·
Free Resource

Download Microservices for Java Developers: A hands-on introduction to frameworks and containers. Brought to you in partnership with Red Hat.

Problem

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
 */
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Property {
    @Nonbinding String value() default "";
    @Nonbinding 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;

    @Property
    @Produces
    public String produceString(final InjectionPoint ip) {
        return this.properties.getProperty(getKey(ip));
    }

    @Property
    @Produces
    public int produceInt(final InjectionPoint ip) {
        return Integer.valueOf(this.properties.getProperty(getKey(ip)));
    }

    @Property
    @Produces
    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();
    }

    @PostConstruct
    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

  @Inject
  @Property
  private String rootFolder;

or

  @Inject
  @Property("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.

Download Building Reactive Microservices in Java: Asynchronous and Event-Based Application Design. Brought to you in partnership with Red Hat

Topics:
cdi ,java ,dependecy injection ,property

Published at DZone with permission of

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}