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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 similar to
 * {@link javax.xml.bind.annotation.XmlValue} 
 * that indicates that results of the annotated "getter" method
 * (which means signature must be that of getters; non-void return
 * type, no args) is to be used as the single value to serialize
 * for the instance. 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 method of a Class can be annotated with this annotation;
 * if more than one is found, an exception may be thrown.
 * Also, if method signature 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 sub-classes 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.
 */
@Target({ElementType.ANNOTATION_TYPE, ElementType.METHOD})
@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;
}