/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.Map;

import org.springframework.core.annotation.AliasFor;

Annotation which indicates that a method parameter should be bound to a web
request parameter.
Supported for annotated handler methods in Spring MVC and Spring WebFlux
as follows:

In Spring MVC, "request parameters" map to query parameters, form data,
and parts in multipart requests. This is because the Servlet API combines
query parameters and form data into a single map called "parameters", and
that includes automatic parsing of the request body.
In Spring WebFlux, "request parameters" map to query parameters only. To work with all 3, query, form data, and multipart data, you can use data binding to a command object annotated with ModelAttribute. 
If the method parameter type is Map and a request parameter name is specified, then the request parameter value is converted to a Map assuming an appropriate conversion strategy is available. 
If the method parameter is Map<String, String> or MultiValueMap<String, String> and a parameter name is not specified, then the map parameter is populated with all request parameter names and values. 
Author:
Arjen Poutsma, Juergen Hoeller, Sam Brannen
See Also:
RequestMapping
RequestHeader
CookieValue
Since:
2.5/**
 * Annotation which indicates that a method parameter should be bound to a web
 * request parameter.
 *
 * <p>Supported for annotated handler methods in Spring MVC and Spring WebFlux
 * as follows:
 * <ul>
 * <li>In Spring MVC, "request parameters" map to query parameters, form data,
 * and parts in multipart requests. This is because the Servlet API combines
 * query parameters and form data into a single map called "parameters", and
 * that includes automatic parsing of the request body.
 * <li>In Spring WebFlux, "request parameters" map to query parameters only.
 * To work with all 3, query, form data, and multipart data, you can use data
 * binding to a command object annotated with {@link ModelAttribute}.
 * </ul>
 *
 * <p>If the method parameter type is {@link Map} and a request parameter name
 * is specified, then the request parameter value is converted to a {@link Map}
 * assuming an appropriate conversion strategy is available.
 *
 * <p>If the method parameter is {@link java.util.Map Map&lt;String, String&gt;} or
 * {@link org.springframework.util.MultiValueMap MultiValueMap&lt;String, String&gt;}
 * and a parameter name is not specified, then the map parameter is populated
 * with all request parameter names and values.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 2.5
 * @see RequestMapping
 * @see RequestHeader
 * @see CookieValue
 */
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RequestParam {

	
Alias for name. /**
	 * Alias for {@link #name}.
	 */
	@AliasFor("name")
	String value() default "";

	
The name of the request parameter to bind to.
Since:
4.2/**
	 * The name of the request parameter to bind to.
	 * @since 4.2
	 */
	@AliasFor("value")
	String name() default "";

	
Whether the parameter is required.
Defaults to true, leading to an exception being thrown if the parameter is missing in the request. Switch this to false if you prefer a null value if the parameter is not present in the request. 
Alternatively, provide a defaultValue, which implicitly sets this flag to false. /**
	 * Whether the parameter is required.
	 * <p>Defaults to {@code true}, leading to an exception being thrown
	 * if the parameter is missing in the request. Switch this to
	 * {@code false} if you prefer a {@code null} value if the parameter is
	 * not present in the request.
	 * <p>Alternatively, provide a {@link #defaultValue}, which implicitly
	 * sets this flag to {@code false}.
	 */
	boolean required() default true;

	
The default value to use as a fallback when the request parameter is
not provided or has an empty value.
Supplying a default value implicitly sets required to false. /**
	 * The default value to use as a fallback when the request parameter is
	 * not provided or has an empty value.
	 * <p>Supplying a default value implicitly sets {@link #required} to
	 * {@code false}.
	 */
	String defaultValue() default ValueConstants.DEFAULT_NONE;

}