001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.juneau.rest.converter;
018
019import org.apache.juneau.http.response.*;
020import org.apache.juneau.rest.*;
021import org.apache.juneau.rest.annotation.*;
022import org.apache.juneau.serializer.*;
023
024/**
025 * REST method response converter.
026 *
027 * <p>
028 * Implements a filter mechanism for REST method calls that allows response objects to be converted to some other POJO
029 * after invocation of the REST method.
030 *
031 * <p>
032 * Converters are associated with REST methods through the following:
033 * <ul class='javatree'>
034 *    <li class='ja'>{@link Rest#converters()}
035 *    <li class='ja'>{@link RestOp#converters()}
036 *    <li class='jm'>{@link org.apache.juneau.rest.RestOpContext.Builder#converters()}
037 * </ul>
038 *
039 * <h5 class='section'>Example:</h5>
040 * <p class='bjava'>
041 *    <jk>public class</jk> RequestEchoResource <jk>extends</jk> BasicRestServlet {
042 *
043 *       <jc>// GET request handler</jc>
044 *       <ja>@RestGet</ja>(path=<js>"/*"</js>, converters={Queryable.<jk>class</jk>,Traversable.<jk>class</jk>})
045 *       <jk>public</jk> HttpServletRequest doGet(RestRequest <jv>req</jv>, RestResponse <jv>res</jv>) {
046 *          <jv>res</jv>.setTitle(<js>"Contents of HttpServletRequest object"</js>);
047 *          <jk>return</jk> <jv>req</jv>;
048 *       }
049 *    }
050 * </p>
051 *
052 * <p>
053 * Converters can also be associated at the servlet level using the {@link Rest#converters() @Rest(converters)} annotation.
054 * <br>Applying converters at the resource level is equivalent to applying converters to each resource method individually.
055 *
056 * <h5 class='topic'>How to implement</h5>
057 *
058 * Implementers should simply implement the {@link #convert(RestRequest, Object)} and return back a 'converted' object.
059 * <br>It's up to the implementer to decide what this means.
060 *
061 * <p>
062 * Subclasses must implement one of the following constructors:
063 * <ul>
064 *    <li><jk>public</jk> T();  <jc>// No-arg constructor</jc>
065 *    <li><jk>public</jk> T(ContextProperties);  <jc>// Property store of the RestContext</jc>
066 * </ul>
067 *
068 * <p>
069 * Subclasses can also be defined as inner classes of the resource class.
070 *
071 * <h5 class='topic'>Predefined converters</h5>
072 * <ul class='javatree'>
073 *    <li class='jc'>{@link Traversable} - Allows URL additional path info to address individual elements in a POJO tree.
074 *    <li class='jc'>{@link Queryable} - Allows query/view/sort functions to be performed on POJOs.
075 *    <li class='jc'>{@link Introspectable} - Allows Java public methods to be invoked on the returned POJOs.
076 * </ul>
077 *
078 * <h5 class='section'>See Also:</h5><ul>
079 *    <li class='jm'>{@link org.apache.juneau.rest.RestOpContext.Builder#converters()}
080 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/Converters">Converters</a>
081 * </ul>
082 * </ul>
083 */
084public interface RestConverter {
085
086   /**
087    * Performs post-call conversion on the specified response object.
088    *
089    * @param req The servlet request.
090    * @param res The response object set by the REST method through the {@link RestResponse#setContent(Object)} method.
091    * @return The converted object.
092    * @throws BasicHttpException Thrown if any errors occur during conversion.
093    * @throws SerializeException Generic serialization error occurred.
094    */
095   Object convert(RestRequest req, Object res) throws BasicHttpException, SerializeException;
096}