jakarta.ws.rs.ext.ParamConverter Maven / Gradle / Ivy

/*
 * Copyright (c) 2012, 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package jakarta.ws.rs.ext;

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 jakarta.ws.rs.DefaultValue;

/**
 * Defines a contract for a delegate responsible for converting between a {@code String} form of a message parameter
 * value and the corresponding custom Java type {@code T}.
 *
 * Conversion of message parameter values injected via {@link jakarta.ws.rs.PathParam @PathParam},
 * {@link jakarta.ws.rs.QueryParam @QueryParam}, {@link jakarta.ws.rs.MatrixParam @MatrixParam},
 * {@link jakarta.ws.rs.FormParam @FormParam}, {@link jakarta.ws.rs.CookieParam @CookieParam} and
 * {@link jakarta.ws.rs.HeaderParam @HeaderParam} is supported.
 * JAX-RS implementations MUST support the {@code ParamConverter} mechanism for all Java types. If a
 * {@code ParamConverter} is available for a type, it MUST be preferred over all other conversion strategies mentioned 
 * in section 3.2 (i.e. single {@code String} argument constructor, static {@code valueOf} or {@code fromString} 
 * methods, etc.).
 * 
 * By default, when used for injection of parameter values, a selected {@code ParamConverter} instance MUST be used
 * eagerly by a JAX-RS runtime to convert any {@link DefaultValue default value} in the resource or provider model, that
 * is during the application deployment, before any value – default or otherwise – is actually required.
 * This conversion strategy ensures that any errors in the default values are reported as early as possible. This
 * default behavior may be overridden by annotating the {@code ParamConverter} implementation class with a {@link Lazy
 * @Lazy} annotation. In such case any default value conversion delegated to the {@code @Lazy}-annotated converter
 * will be deferred to a latest possible moment (i.e. until the injection of such default value is required).
 * 
 * 
 * NOTE: A service implementing this contract is not recognized as a registrable JAX-RS extension provider. Instead, a
 * {@link ParamConverterProvider} instance responsible for providing {@code ParamConverter} instances has to be
 * registered as one of the JAX-RS extension providers.
 * 
 *
 * @param  the supported Java type convertible to/from a {@code String} format.
 * @author Marek Potociar
 * @since 2.0
 */
public interface ParamConverter {

    /**
     * Mandates that a conversion of any {@link DefaultValue default value} delegated to a {@link ParamConverter parameter
     * converter} annotated with {@code @Lazy} annotation SHOULD occur only once the value is actually required (e.g. to be
     * injected for the first time).
     *
     * @since 2.0
     */
    @Target({ ElementType.TYPE })
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public static @interface Lazy {
    }

    /**
     * Parse the supplied value and create an instance of {@code T}.
     *
     * @param value the string value.
     * @return the newly created instance of {@code T}.
     *
     * @throws IllegalArgumentException if the supplied string cannot be parsed or is {@code null}.
     */
    public T fromString(String value);

    /**
     * Convert the supplied value to a String.
     * 
     * This method is reserved for future use. Proprietary JAX-RS extensions may leverage the method. Users should be aware
     * that any such support for the method comes at the expense of producing non-portable code.
     * 
     *
     * @param value the value of type {@code T}.
     * @return a String representation of the value.
     *
     * @throws IllegalArgumentException if the supplied object cannot be serialized or is {@code null}.
     */
    public String toString(T value);
}