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package io.quarkus.runtime.annotations;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Used to mark a configuration object as safe to be initialized during the STATIC INIT phase.
 * 
 * The target configuration objects include {@link org.eclipse.microprofile.config.spi.ConfigSource},
 * {@link org.eclipse.microprofile.config.spi.ConfigSourceProvider}, {@link io.smallrye.config.ConfigSourceFactory} and
 * {@link io.smallrye.config.ConfigMapping}. Moreover, this annotation can be used for
 * {@link org.eclipse.microprofile.config.inject.ConfigProperty} injection points.
 * 

 *
 * When a Quarkus application is starting up, Quarkus will execute first a static init method which contains some
 * extensions actions and configurations. Example:
 *
 * 
 * // Auto Generated by Quarkus
 * public class Application {
 *     static {
 *         Config config = ConfigProvider.getConfig();
 *         String url = config.getValue("database.url", String.class);
 *         String login = config.getValue("database.login", String.class);
 *         String password = config.getValue("database.password", String.class);
 *
 *         initDatabase(url, login, password);
 *     }
 * }
 * 
 *
 * Please check Initializing Fields for
 * more information about static blocks.
 *
 * Since Config initializes first, some ConfigSources may not be suited to be initialized at static init. Consider the
 * previous code example and a ConfigSource that requires database access. In this case, it is impossible to properly
 * initialize such ConfigSource, because the database services are not yet available so the ConfigSource in unusable.
 */
@Target({ TYPE, FIELD, PARAMETER })
@Retention(RUNTIME)
@Documented
public @interface StaticInitSafe {
}