ConfigProperty.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.deltaspike.core.api.config;

import javax.enterprise.util.Nonbinding;
import javax.inject.Qualifier;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.CONSTRUCTOR;
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.ANNOTATION_TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * This Qualifier allows simple injection of configuration properties through the DeltaSpike configuration 
 * mechanism.
 * <p>
 * A default implementation is provided in DeltaSpike for basic String injection points:
 * <pre>
 *   @Inject @ConfigProperty(name="locationId")
 *   private String locationId;
 * </pre>
 * </p>
 * <p>
 * It's possible to use config properties in a type-safe manner, which requires a custom producer:
 *
 * <pre>
 *   @Target({FIELD, METHOD})
 *   @Retention(RUNTIME)
 *   @ConfigProperty(name = "locationId")
 *   @Qualifier
 *   public @interface Location {
 *   }
 * </pre>
 *
 * <pre>
 *   @Location
 *   private String locationId;
 * </pre>
 *
 *  <pre>
 *   @ApplicationScoped
 *   public class CustomConfigPropertyProducer extends BaseConfigPropertyProducer {
 *     @Produces
 *     @Dependent
 *     @Location
 *     public String produceLocationId(InjectionPoint injectionPoint) {
 *       String configuredValue = getStringPropertyValue(injectionPoint);
 *       if (configuredValue == null) {
 *         return null;
 *       }
 *       return configuredValue;
 *     }
 *   }
 * </pre>
 * </p>
 * <p>
 * Producers can be implemented to support other types of injection points:
 * <pre>
 *   @Inject
 *   @Location
 *   private LocationId locationId;
 * </pre>
 *
 * <pre>
 *   @ApplicationScoped
 *   public class CustomConfigPropertyProducer extends BaseConfigPropertyProducer {
 *     @Produces
 *     @Dependent
 *     @Location
 *     public LocationId produceLocationId(InjectionPoint injectionPoint) {
 *       String configuredValue = getStringPropertyValue(injectionPoint);
 *       if (configuredValue == null) {
 *         return null;
 *       }
 *       return LocationId.valueOf(configuredValue.trim().toUpperCase());
 *     }
 *   }
 * </pre>
 * </p>
 * For custom producer implementations, {@link org.apache.deltaspike.core.spi.config.BaseConfigPropertyProducer} can
 * be used as the base class.
 * 
 * @see org.apache.deltaspike.core.api.config.ConfigResolver
 * @see org.apache.deltaspike.core.spi.config.BaseConfigPropertyProducer
 */
@Target({ PARAMETER, FIELD, METHOD, CONSTRUCTOR, ANNOTATION_TYPE })
@Retention(RUNTIME)
@Documented
@Qualifier
public @interface ConfigProperty
{
    /**
     * This constant is a workaround for the java restriction that Annotation values cannot be set to null. Do not use
     * this String in your configuration.
     */
    String NULL = "org.apache.deltaspike.NullValueMarker";

    /**
     * Name/key of the property.
     * @return name of the property
     */
    @Nonbinding
    String name();

    /**
     * <b>Optional</b> default value.
     *
     * @return the default value which should be used if no config value could be found
     */
    @Nonbinding
    String defaultValue() default NULL;

    @Nonbinding
    boolean projectStageAware() default true;

    @Nonbinding
    String parameterizedBy() default NULL;

    /**
     * Whether to resolve 'variables' in configured values.
     *
     * @see org.apache.deltaspike.core.api.config.ConfigResolver.TypedResolver#evaluateVariables(boolean)
     */
    @Nonbinding
    boolean evaluateVariables() default true;

    /**
     * Converter for this property.
     * @return the converter to use to read this property in the expected type.
     */
    @Nonbinding
    Class<? extends ConfigResolver.Converter> converter() default ConfigResolver.Converter.class;
}