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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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// ***************************************************************************************************************************
package org.apache.juneau.http.annotation;

import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;

import java.lang.annotation.*;
import java.util.*;

import org.apache.juneau.jsonschema.annotation.Items;
import org.apache.juneau.*;
import org.apache.juneau.annotation.*;
import org.apache.juneau.httppart.*;
import org.apache.juneau.json.*;
import org.apache.juneau.jsonschema.*;
import org.apache.juneau.oapi.*;

/**
 * REST request header annotation.
 *
 * <p>
 * Identifies a POJO to be used as the header of an HTTP request.
 *
 * <p>
 * Can be used in the following locations:
 * <ul>
 *    <li>Arguments and argument-types of server-side <ja>@RestMethod</ja>-annotated methods.
 *    <li>Arguments and argument-types of client-side <ja>@RemoteResource</ja>-annotated interfaces.
 *    <li>Methods and return types of server-side and client-side <ja>@Request</ja>-annotated interfaces.
 * </ul>
 *
 * <h5 class='topic'>Arguments and argument-types of server-side @RestMethod-annotated methods</h5>
 *
 * Annotation that can be applied to a parameter of a <ja>@RestMethod</ja>-annotated method to identify it as a HTTP
 * request header.
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bcode w800'>
 *    <ja>@RestMethod</ja>(name=<jsf>GET</jsf>)
 *    <jk>public void</jk> doGet(<ja>@Header</ja>(<js>"ETag"</js>) UUID etag) {...}
 * </p>
 *
 * <p>
 * This is functionally equivalent to the following code...
 * <p class='bcode w800'>
 *    <ja>@RestMethod</ja>(name=<jsf>GET</jsf>)
 *    <jk>public void</jk> doPostPerson(RestRequest req, RestResponse res) {
 *       UUID etag = req.getHeader(UUID.<jk>class</jk>, <js>"ETag"</js>);
 *       ...
 *    }
 * </p>
 *
 * <ul class='seealso'>
 *    <li class='link'>{@doc juneau-rest-server.HttpPartAnnotations.Header}
 *    <li class='link'>{@doc juneau-rest-server.Swagger}
 *    <li class='extlink'>{@doc SwaggerParameterObject}
 * </ul>
 *
 * <h5 class='topic'>Arguments and argument-types of client-side @RemoteResource-annotated interfaces</h5>
 *
 * Annotation applied to Java method arguments of interface proxies to denote that they are serialized as an HTTP
 * header value.
 *
 * <ul class='seealso'>
 *    <li class='link'>{@doc juneau-rest-client.RestProxies.Header}
 * </ul>
 *
 * <h5 class='topic'>Methods and return types of server-side and client-side @Request-annotated interfaces</h5>
 *
 * <ul class='seealso'>
 *    <li class='link'>{@doc juneau-rest-server.HttpPartAnnotations.Request}
 *    <li class='link'>{@doc juneau-rest-client.RestProxies.Request}
 * </ul>
 */
@Documented
@Target({PARAMETER,FIELD,METHOD,TYPE})
@Retention(RUNTIME)
@Inherited
public @interface Header {

   /**
    * Skips this value during serialization if it's an empty string or empty collection/array.
    *
    * <p>
    * Note that <jk>null</jk> values are already ignored.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Client-side schema-based serializing.
    * </ul>
    */
   boolean skipIfEmpty() default false;

   /**
    * Specifies the {@link HttpPartSerializer} class used for serializing values to strings.
    *
    * <p>
    * Overrides for this part the part serializer defined on the REST client which by default is {@link OpenApiSerializer}.
    */
   Class<? extends HttpPartSerializer> serializer() default HttpPartSerializer.Null.class;

   /**
    * Specifies the {@link HttpPartParser} class used for parsing strings to values.
    *
    * <p>
    * Overrides for this part the part parser defined on the REST resource which by default is {@link OpenApiParser}.
    */
   Class<? extends HttpPartParser> parser() default HttpPartParser.Null.class;

   //=================================================================================================================
   // Attributes common to all Swagger Parameter objects
   //=================================================================================================================

   /**
    * HTTP header name.
    * <p>
    * A blank value (the default) indicates to reuse the bean property name when used on a request bean property.
    *
    * <p>
    * The value should be either a valid HTTP header name, or <js>"*"</js> to represent multiple name/value pairs
    *
    * <p>
    * A blank value (the default) has the following behavior:
    * <ul class='spaced-list'>
    *    <li>
    *       If the data type is <c>NameValuePairs</c>, <c>Map</c>, or a bean,
    *       then it's the equivalent to <js>"*"</js> which will cause the value to be serialized as name/value pairs.
    *
    *       <h5 class='figure'>Examples:</h5>
    *       <p class='bcode w800'>
    *    <jc>// When used on a REST method</jc>
    *    <ja>@RestMethod</ja>(path=<js>"/addPet"</js>)
    *    <jk>public void</jk> addPet(<ja>@Header</ja> ObjectMap allHeaderParameters) {...}
    *       </p>
    *       <p class='bcode w800'>
    *    <jc>// When used on a remote method parameter</jc>
    *    <ja>@RemoteResource</ja>(path=<js>"/myproxy"</js>)
    *    <jk>public interface</jk> MyProxy {
    *
    *       <jc>// Equivalent to @Header("*")</jc>
    *       <ja>@RemoteMethod</ja>(path=<js>"/mymethod"</js>)
    *       String myProxyMethod1(<ja>@Header</ja> Map&lt;String,Object&gt; allHeaderParameters);
    *    }
    *       </p>
    *       <p class='bcode w800'>
    *    <jc>// When used on a request bean method</jc>
    *    <jk>public interface</jk> MyRequest {
    *
    *       <jc>// Equivalent to @Header("*")</jc>
    *       <ja>@Header</ja>
    *       Map&lt;String,Object&gt; getFoo();
    *    }
    *       </p>
    *    </li>
    *    <li>
    *       If used on a request bean method, uses the bean property name.
    *
    *       <h5 class='figure'>Example:</h5>
    *       <p class='bcode w800'>
    *    <jk>public interface</jk> MyRequest {
    *
    *       <jc>// Equivalent to @Header("Foo")</jc>
    *       <ja>@Header</ja>
    *       <ja>@BeanProperty</ja>(<js>"Foo"</js>)
    *       String getFoo();
    *    }
    *       </p>
    *    </li>
    * </ul>
    */
   String name() default "";

   /**
    * A synonym for {@link #name()}.
    *
    * <p>
    * Allows you to use shortened notation if you're only specifying the name.
    *
    * <p>
    * The following are completely equivalent ways of defining a header entry:
    * <p class='bcode w800'>
    *    <jk>public</jk> Order placeOrder(<ja>@Header</ja>(name=<js>"api_key"</js>) String apiKey) {...}
    * </p>
    * <p class='bcode w800'>
    *    <jk>public</jk> Order placeOrder(<ja>@Header</ja>(<js>"api_key"</js>) String apiKey) {...}
    * </p>
    */
   String value() default "";

   /**
    * <mk>description</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * A brief description of the parameter. This could contain examples of use.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side generated Swagger documentation.
    * </ul>
    *
    * <ul class='notes'>
    *    <li>
    *       The format is plain text.
    *       <br>Multiple lines are concatenated with newlines.
    *    <li>
    *       Supports {@doc DefaultRestSvlVariables}
    *       (e.g. <js>"$L{my.localized.variable}"</js>).
    * </ul>
    */
   String[] description() default {};

   /**
    * <mk>required</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Determines whether the parameter is mandatory.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   boolean required() default false;

   //=================================================================================================================
   // Attributes specific to parameters other than body
   //=================================================================================================================

   /**
    * <mk>type</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * The type of the parameter.
    *
    * <p>
    * The possible values are:
    * <ul class='spaced-list'>
    *    <li>
    *       <js>"string"</js>
    *       <br>Parameter must be a string or a POJO convertible from a string.
    *    <li>
    *       <js>"number"</js>
    *       <br>Parameter must be a number primitive or number object.
    *       <br>If parameter is <c>Object</c>, creates either a <c>Float</c> or <c>Double</c> depending on the size of the number.
    *    <li>
    *       <js>"integer"</js>
    *       <br>Parameter must be a integer/long primitive or integer/long object.
    *       <br>If parameter is <c>Object</c>, creates either a <c>Short</c>, <c>Integer</c>, or <c>Long</c> depending on the size of the number.
    *    <li>
    *       <js>"boolean"</js>
    *       <br>Parameter must be a boolean primitive or object.
    *    <li>
    *       <js>"array"</js>
    *       <br>Parameter must be an array or collection.
    *       <br>Elements must be strings or POJOs convertible from strings.
    *       <br>If parameter is <c>Object</c>, creates an {@link ObjectList}.
    *    <li>
    *       <js>"object"</js>
    *       <br>Parameter must be a map or bean.
    *       <br>If parameter is <c>Object</c>, creates an {@link ObjectMap}.
    *       <br>Note that this is an extension of the OpenAPI schema as Juneau allows for arbitrarily-complex POJOs to be serialized as HTTP parts.
    *    <li>
    *       <js>"file"</js>
    *       <br>This type is currently not supported.
    * </ul>
    *
    * <p>
    * Static strings are defined in {@link ParameterType}.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing.
    * </ul>
    *
    * <ul class='seealso'>
    *    <li class='extlink'>{@doc SwaggerDataTypes}
    * </ul>
    */
   String type() default "";

   /**
    * <mk>format</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * The extending format for the previously mentioned {@doc SwaggerParameterTypes parameter type}.
    *
    * <p>
    * The possible values are:
    * <ul class='spaced-list'>
    *    <li>
    *       <js>"int32"</js> - Signed 32 bits.
    *       <br>Only valid with type <js>"integer"</js>.
    *    <li>
    *       <js>"int64"</js> - Signed 64 bits.
    *       <br>Only valid with type <js>"integer"</js>.
    *    <li>
    *       <js>"float"</js> - 32-bit floating point number.
    *       <br>Only valid with type <js>"number"</js>.
    *    <li>
    *       <js>"double"</js> - 64-bit floating point number.
    *       <br>Only valid with type <js>"number"</js>.
    *    <li>
    *       <js>"byte"</js> - BASE-64 encoded characters.
    *       <br>Only valid with type <js>"string"</js>.
    *       <br>Parameters of type POJO convertible from string are converted after the string has been decoded.
    *    <li>
    *       <js>"binary"</js> - Hexadecimal encoded octets (e.g. <js>"00FF"</js>).
    *       <br>Only valid with type <js>"string"</js>.
    *       <br>Parameters of type POJO convertible from string are converted after the string has been decoded.
    *    <li>
    *       <js>"date"</js> - An <a href='http://xml2rfc.ietf.org/public/rfc/html/rfc3339.html#anchor14'>RFC3339 full-date</a>.
    *       <br>Only valid with type <js>"string"</js>.
    *    <li>
    *       <js>"date-time"</js> - An <a href='http://xml2rfc.ietf.org/public/rfc/html/rfc3339.html#anchor14'>RFC3339 date-time</a>.
    *       <br>Only valid with type <js>"string"</js>.
    *    <li>
    *       <js>"password"</js> - Used to hint UIs the input needs to be obscured.
    *       <br>This format does not affect the serialization or parsing of the parameter.
    *    <li>
    *       <js>"uon"</js> - UON notation (e.g. <js>"(foo=bar,baz=@(qux,123))"</js>).
    *       <br>Only valid with type <js>"object"</js>.
    *       <br>If not specified, then the input is interpreted as plain-text and is converted to a POJO directly.
    * </ul>
    *
    * <p>
    * Static strings are defined in {@link FormatType}.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing.
    * </ul>
    *
    * <ul class='seealso'>
    *    <li class='extlink'>{@doc SwaggerDataTypeFormats}
    * </ul>
    */
   String format() default "";


   /**
    * <mk>allowEmptyValue</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Sets the ability to pass empty-valued heaver values.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    *
    * <p>
    * <b>Note:</b>  This is technically only valid for either query or formData parameters, but support is provided anyway for backwards compatability.
    */
   boolean allowEmptyValue() default false;

   /**
    * <mk>items</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Describes the type of items in the array.
    *
    * <p>
    * Required if <c>type</c> is <js>"array"</js>.
    * <br>Can only be used if <c>type</c> is <js>"array"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing and parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing and serializing validation.
    * </ul>
    */
   Items items() default @Items;

   /**
    * <mk>collectionFormat</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Determines the format of the array if <c>type</c> <js>"array"</js> is used.
    * <br>Can only be used if <c>type</c> is <js>"array"</js>.
    *
    * <br>Possible values are:
    * <ul class='spaced-list'>
    *    <li>
    *       <js>"csv"</js> (default) - Comma-separated values (e.g. <js>"foo,bar"</js>).
    *    <li>
    *       <js>"ssv"</js> - Space-separated values (e.g. <js>"foo bar"</js>).
    *    <li>
    *       <js>"tsv"</js> - Tab-separated values (e.g. <js>"foo\tbar"</js>).
    *    <li>
    *       <js>"pipes</js> - Pipe-separated values (e.g. <js>"foo|bar"</js>).
    *    <li>
    *       <js>"uon"</js> - UON notation (e.g. <js>"@(foo,bar)"</js>).
    *    <li>
    * </ul>
    *
    * <p>
    * Static strings are defined in {@link CollectionFormatType}.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing.
    * </ul>
    *
    * <p>
    * Note that for collections/arrays parameters with POJO element types, the input is broken into a string array before being converted into POJO elements.
    */
   String collectionFormat() default "";

   /**
    * <mk>default</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Declares the value of the parameter that the server will use if none is provided, for example a "count" to control the number of results per page might default to 100 if not supplied by the client in the request.
    * <br>(Note: "default" has no meaning for required parameters.)
    *
    * <p>
    * Additionally, this value is used to create instances of POJOs that are then serialized as language-specific examples in the generated Swagger documentation
    * if the examples are not defined in some other way.
    *
    * <p>
    * The format of this value is a string.
    * <br>Multiple lines are concatenated with newlines.
    *
    * <h5 class='section'>Examples:</h5>
    * <p class='bcode w800'>
    *    <jk>public</jk> Order placeOrder(
    *       <ja>@Header</ja>(name=<js>"X-PetId"</js>, _default=<js>"100"</js>) <jk>long</jk> petId,
    *       <ja>@Header</ja>(name=<js>"X-AdditionalInfo"</js>, format=<js>"uon"</js>, _default=<js>"(rushOrder=false)"</js>) AdditionalInfo additionalInfo,
    *       <ja>@Header</ja>(name=<js>"X-Flags"</js>, collectionFormat=<js>"uon"</js>, _default=<js>"@(new-customer)"</js>) String[] flags
    *    ) {...}
    * </p>
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing.
    * </ul>
    */
   String[] _default() default {};

   /**
    * <mk>maximum</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Defines the maximum value for a parameter of numeric types.
    * <br>The value must be a valid JSON number.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"integer"</js>, <js>"number"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   String maximum() default "";

   /**
    * <mk>exclusiveMaximum</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Defines whether the maximum is matched exclusively.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"integer"</js>, <js>"number"</js>.
    * <br>If <jk>true</jk>, must be accompanied with <c>maximum</c>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   boolean exclusiveMaximum() default false;

   /**
    * <mk>minimum</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Defines the minimum value for a parameter of numeric types.
    * <br>The value must be a valid JSON number.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"integer"</js>, <js>"number"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   String minimum() default "";

   /**
    * <mk>exclusiveMinimum</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * Defines whether the minimum is matched exclusively.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"integer"</js>, <js>"number"</js>.
    * <br>If <jk>true</jk>, must be accompanied with <c>minimum</c>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   boolean exclusiveMinimum() default false;

   /**
    * <mk>maxLength</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * A string instance is valid against this keyword if its length is less than, or equal to, the value of this keyword.
    * <br>The length of a string instance is defined as the number of its characters as defined by <a href='https://tools.ietf.org/html/rfc4627'>RFC 4627</a>.
    * <br>The value <c>-1</c> is always ignored.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"string"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   long maxLength() default -1;

   /**
    * <mk>minLength</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * A string instance is valid against this keyword if its length is greater than, or equal to, the value of this keyword.
    * <br>The length of a string instance is defined as the number of its characters as defined by <a href='https://tools.ietf.org/html/rfc4627'>RFC 4627</a>.
    * <br>The value <c>-1</c> is always ignored.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"string"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   long minLength() default -1;

   /**
    * <mk>pattern</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * A string input is valid if it matches the specified regular expression pattern.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"string"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   String pattern() default "";

   /**
    * <mk>maxItems</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * An array or collection is valid if its size is less than, or equal to, the value of this keyword.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"array"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   long maxItems() default -1;

   /**
    * <mk>minItems</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * An array or collection is valid if its size is greater than, or equal to, the value of this keyword.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"array"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   long minItems() default -1;

   /**
    * <mk>uniqueItems</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * If <jk>true</jk> the input validates successfully if all of its elements are unique.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * If the parameter type is a subclass of {@link Set}, this validation is skipped (since a set can only contain unique items anyway).
    * <br>Otherwise, the collection or array is checked for duplicate items.
    *
    * <p>
    * Only allowed for the following types: <js>"array"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   boolean uniqueItems() default false;

   /**
    * <mk>enum</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * If specified, the input validates successfully if it is equal to one of the elements in this array.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * The format is a {@doc SimpleJson} array or comma-delimited list.
    * <br>Multiple lines are concatenated with newlines.
    *
    * <h5 class='section'>Examples:</h5>
    * <p class='bcode w800'>
    *    <jc>// Comma-delimited list</jc>
    *    <jk>public</jk> Collection&lt;Pet&gt; findPetsByStatus(
    *       <ja>@Header</ja>(
    *          name=<js>"X-Status"</js>,
    *          _enum=<js>"AVAILABLE,PENDING,SOLD"</js>,
    *       ) PetStatus status
    *    ) {...}
    * </p>
    * <p class='bcode w800'>
    *    <jc>// JSON array</jc>
    *    <jk>public</jk> Collection&lt;Pet&gt; findPetsByStatus(
    *       <ja>@Header</ja>(
    *          name=<js>"X-Status"</js>,
    *          _enum=<js>"['AVAILABLE','PENDING','SOLD']"</js>,
    *       ) PetStatus status
    *    ) {...}
    * </p>
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   String[] _enum() default {};

   /**
    * <mk>multipleOf</mk> field of the {@doc SwaggerParameterObject}.
    *
    * <p>
    * A numeric instance is valid if the result of the division of the instance by this keyword's value is an integer.
    * <br>The value must be a valid JSON number.
    *
    * <p>
    * If validation fails during serialization or parsing, the part serializer/parser will throw a {@link SchemaValidationException}.
    * <br>On the client-side, this gets converted to a <c>RestCallException</c> which is thrown before the connection is made.
    * <br>On the server-side, this gets converted to a <c>BadRequest</c> (400).
    *
    * <p>
    * Only allowed for the following types: <js>"integer"</js>, <js>"number"</js>.
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side schema-based parsing validation.
    *    <li>
    *       Server-side generated Swagger documentation.
    *    <li>
    *       Client-side schema-based serializing validation.
    * </ul>
    */
   String multipleOf() default "";

   //=================================================================================================================
   // Other
   //=================================================================================================================

   /**
    * A serialized example of the parameter.
    *
    * <p>
    * This attribute defines a representation of the value that is used by <c>BasicRestInfoProvider</c> to construct
    * an example of parameter.
    *
    * <h5 class='section'>Example:</h5>
    * <p class='bcode w800'>
    *    <ja>@Header</ja>(
    *       name=<js>"Status"</js>,
    *       type=<js>"array"</js>,
    *       collectionFormat=<js>"csv"</js>,
    *       example=<js>"AVALIABLE,PENDING"</js>
    *    )
    *    PetStatus[] status
    * </p>
    *
    * <p>
    * If not specified, Juneau will automatically create examples from sample POJOs serialized using the registered {@link HttpPartSerializer}.
    * <br>
    *
    * </p>
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side generated Swagger documentation.
    * </ul>
    *
    * <ul class='seealso'>
    *    <li class='ja'>{@link Example}
    *    <li class='jc'>{@link BeanContext}
    *    <ul>
    *       <li class='jf'>{@link BeanContext#BEAN_examples BEAN_examples}
    *    </ul>
    *    <li class='jc'>{@link JsonSchemaSerializer}
    *    <ul>
    *       <li class='jf'>{@link JsonSchemaGenerator#JSONSCHEMA_addExamplesTo JSONSCHEMA_addExamplesTo}
    *       <li class='jf'>{@link JsonSchemaGenerator#JSONSCHEMA_allowNestedExamples JSONSCHEMA_allowNestedExamples}
    *    </ul>
    * </ul>
    *
    * <ul class='notes'>
    *    <li>
    *       The format is a {@doc SimpleJson} object or plain text string.
    *       <br>Multiple lines are concatenated with newlines.
    *    <li>
    *       Supports {@doc DefaultRestSvlVariables}
    *       (e.g. <js>"$L{my.localized.variable}"</js>).
    * </ul>
    */
   String[] example() default {};

   /**
    * Free-form value for the {@doc SwaggerParameterObject}.
    *
    * <p>
    * This is a JSON object that makes up the swagger information for this field.
    *
    * <p>
    * The following are completely equivalent ways of defining the swagger description of the request header:
    * <p class='bcode w800'>
    *    <jc>// Normal</jc>
    *    <ja>@Header</ja>(
    *       name=<js>"api_key"</js>,
    *       description=<js>"Security API key"</js>,
    *       required=<jk>true</jk>,
    *       example=<js>"foobar"</js>
    *    )
    * </p>
    * <p class='bcode w800'>
    *    <jc>// Free-form</jc>
    *    <ja>@Header</ja>(
    *       name=<js>"api_key"</js>,
    *       api={
    *          <js>"description: 'Security API key',"</js>,
    *          <js>"required: true,"</js>,
    *          <js>"example: 'foobar'"</js>
    *       }
    *    )
    * </p>
    * <p class='bcode w800'>
    *    <jc>// Free-form with variables</jc>
    *    <ja>@Header</ja>(
    *       name=<js>"api_key"</js>,
    *       api=<js>"$L{apiKeySwagger}"</js>
    *    )
    * </p>
    * <p class='bcode w800'>
    *    <mc>// Contents of MyResource.properties</mc>
    *    <mk>apiKeySwagger</mk> = <mv>{ description: "Security API key", required: true, example: "foobar" }</mv>
    * </p>
    *
    * <p>
    *    The reasons why you may want to use this field include:
    * <ul>
    *    <li>You want to pull in the entire Swagger JSON definition for this field from an external source such as a properties file.
    *    <li>You want to add extra fields to the Swagger documentation that are not officially part of the Swagger specification.
    * </ul>
    *
    * <h5 class='section'>Used for:</h5>
    * <ul class='spaced-list'>
    *    <li>
    *       Server-side generated Swagger documentation.
    * </ul>
    *
    * <ul class='notes'>
    *    <li>
    *       Note that the only swagger field you can't specify using this value is <js>"name"</js> whose value needs to be known during servlet initialization.
    *    <li>
    *       The format is a {@doc SimpleJson} object.
    *    <li>
    *       Automatic validation is NOT performed on input based on attributes in this value.
    *    <li>
    *       The leading/trailing <c>{ }</c> characters are optional.
    *       <br>The following two example are considered equivalent:
    *       <p class='bcode w800'>
    *    <ja>@Header</ja>(api=<js>"{required: true}"</js>)
    *       </p>
    *       <p class='bcode w800'>
    *    <ja>@Header</ja>(api=<js>"required: true"</js>)
    *       </p>
    *    <li>
    *       Multiple lines are concatenated with newlines so that you can format the value to be readable.
    *    <li>
    *       Supports {@doc DefaultRestSvlVariables}
    *       (e.g. <js>"$L{my.localized.variable}"</js>).
    *    <li>
    *       Values defined in this field supersede values pulled from the Swagger JSON file and are superseded by individual values defined on this annotation.
    * </ul>
    */
   String[] api() default {};
}