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package com.fasterxml.jackson.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Marker annotation
 * that indicates that the value of annotated accessor (either field
 * or "getter" method [a method with non-void return type, no args])
 * is to be used as the single value to serialize for the instance,
 * instead of the usual method of collecting properties of value.
 * Usually value will be of a simple scalar type
 * (String or Number), but it can be any serializable type (Collection,
 * Map or Bean).
 *
 * At most one accessor of a Class can be annotated with this annotation;
 * if more than one is found, an exception may be thrown.
 * Also, if method signature of annotated method is not compatible with Getters,
 * an exception may be thrown (whether exception is thrown or not is an
 * implementation detail (due to filtering during introspection, some annotations
 * may be skipped) and applications should not rely on specific behavior).
 *

 * A typical usage is that of annotating toString()
 * method so that returned String value is used as the JSON serialization;
 * and if deserialization is needed, there is matching constructor
 * or factory method annotated with {@link JsonCreator} annotation.
 *

 * Boolean argument is only used so that subclasses can "disable"
 * annotation if necessary.
 *

 * NOTE: when use for Java enums, one additional feature is
 * that value returned by annotated method is also considered to be the
 * value to deserialize from, not just JSON String to serialize as.
 * This is possible since set of Enum values is constant and it is possible
 * to define mapping, but can not be done in general for POJO types; as such,
 * this is not used for POJO deserialization.
 *
 * NOTE: When the instance is being serialized as the key of a Map type,
 * this will be ignored if an accessor is annotated with
 * {@link JsonKey}.
 *
 * @see JsonCreator
 * @see JsonKey
 */
@Target({ElementType.ANNOTATION_TYPE, ElementType.METHOD,
    ElementType.FIELD // since 2.9
})
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonValue
{
    /**
     * Optional argument that defines whether this annotation is active
     * or not. The only use for value 'false' if for overriding purposes.
     * Overriding may be necessary when used
     * with "mix-in annotations" (aka "annotation overrides").
     * For most cases, however, default value of "true" is just fine
     * and should be omitted.
     */
    boolean value() default true;
}