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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.
* This value will be used only if the instance is being serialized
* as a key in a Map type.
* 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.
*
* @see JsonValue
*/
@Target({ElementType.ANNOTATION_TYPE, ElementType.METHOD,
ElementType.FIELD
})
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonKey
{
/**
* 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;
}