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Core annotations used for value types, used by Jackson data binding package.
There is a newer version: 2.18.0-rc1
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 can be used to define a non-static
 * method as a "setter" or "getter" for a logical property
 * (depending on its signature),
 * or non-static object field to be used (serialized, deserialized) as
 * a logical property.
 *
 * Default value ("") indicates that the field name is used
 * as the property name without any modifications, but it
 * can be specified to non-empty value to specify different
 * name. Property name refers to name used externally, as
 * the field name in JSON objects.
 */
@Target({ElementType.ANNOTATION_TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonProperty
{
    /**
     * Special value that indicates that handlers should use the default
     * name (derived from method or field name) for property.
     * 
     * @since 2.1
     */
    public final static String USE_DEFAULT_NAME = "";

    /**
     * Marker value used to indicate that no index has been specified.
     * Used as the default value as annotations do not allow "missing"
     * values.
     * 
     * @since 2.4
     */
    public final static int INDEX_UNKNOWN = -1;
    
    /**
     * Defines name of the logical property, i.e. JSON object field
     * name to use for the property. If value is empty String (which is the
     * default), will try to use name of the field that is annotated.
     * Note that there is
     * no default name available for constructor arguments,
     * meaning that
     * Empty String is not a valid value for constructor arguments.
     */
    String value() default USE_DEFAULT_NAME;

    /**
     * Property that indicates whether a value (which may be explicit
     * null) is expected for property during deserialization or not.
     * If expected, BeanDeserialized should indicate
     * this as a validity problem (usually by throwing an exception,
     * but this may be sent via problem handlers that can try to
     * rectify the problem, for example, by supplying a default
     * value).
     *
     * Note that as of 2.0, this property is NOT used by
     * BeanDeserializer: support is expected to be
     * added for a later minor version.
     * 
     * @since 2.0
     */
    boolean required() default false;

    /**
     * Property that indicates numerical index of this property (relative
     * to other properties specified for the Object). This index
     * is typically used by binary formats, but may also be useful
     * for schema languages and other tools.
     * 
     * @since 2.4
     */
    int index() default INDEX_UNKNOWN;

    /**
     * Property that may be used to document expected default value
     * for the property: most often used as source information for generating
     * schemas (like JSON Schema or protobuf/thrift schema), or documentation.
     * It may also be used by Jackson extension modules; core jackson databind
     * does not have any automated handling beyond simply exposing this
     * value through bean property introspection.
     *
     * @since 2.5
     */
    String defaultValue() default "";
}