com.google.inject.multibindings.ProvidesIntoOptional Maven / Gradle / Ivy

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package com.google.inject.multibindings;

import com.google.inject.Module;

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

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Annotates methods of a {@link Module} to add items to a {@link Multibinder}.
 * The method's return type and binding annotation determines what Optional this will
 * contribute to. For example,
 *
 *  * {@literal @}ProvidesIntoOptional(DEFAULT)
 * {@literal @}Named("url")
 * String provideFooUrl(FooManager fm) { returm fm.getUrl(); }
 *
 * {@literal @}ProvidesIntoOptional(ACTUAL)
 * {@literal @}Named("url")
 * String provideBarUrl(BarManager bm) { return bm.getUrl(); }
 * 
 *
 * will set the default value of {@code @Named("url") Optional} to foo's URL,
 * and then override it to bar's URL.
 */
@Documented
@Target(METHOD)
@Retention(RUNTIME)
public @interface ProvidesIntoOptional {
    /**
     * Specifies if the binding is for the actual or default value.
     */
    Type value();

    enum Type {
        /**
         * Corresponds to {@link OptionalBinder#setBinding}.
         */
        ACTUAL,

        /**
         * Corresponds to {@link OptionalBinder#setDefault}.
         */
        DEFAULT
    }
}