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012// ***************************************************************************************************************************
013package org.apache.juneau.rest;
014
015import org.apache.juneau.rest.annotation.*;
016import org.apache.juneau.rest.converters.*;
017import org.apache.juneau.serializer.*;
018
019/**
020 * REST method response converter.
021 * 
022 * <p>
023 * Implements a filter mechanism for REST method calls that allows response objects to be converted to some other POJO
024 * after invocation of the REST method.
025 * 
026 * <p>
027 * Converters are associated with REST methods through the following:
028 * <ul>
029 *    <li class='ja'>{@link RestResource#converters()}
030 *    <li class='ja'>{@link RestMethod#converters()}
031 *    <li class='jf'>{@link RestContext#REST_converters}
032 *    <li class='jm'>{@link RestContextBuilder#converters(Class...)}
033 *    <li class='jm'>{@link RestContextBuilder#converters(RestConverter...)}
034 * </ul>
035 * 
036 * <h5 class='section'>Example:</h5>
037 * <p class='bcode'>
038 *    <jk>public class</jk> RequestEchoResource <jk>extends</jk> RestServlet {
039 * 
040 *       <jc>// GET request handler</jc>
041 *       <ja>@RestMethod</ja>(name=<jsf>GET</jsf>, path=<js>"/*"</js>, converters={Queryable.<jk>class</jk>,Traversable.<jk>class</jk>})
042 *       <jk>public</jk> HttpServletRequest doGet(RestRequest req) {
043 *          res.setTitle(<js>"Contents of HttpServletRequest object"</js>);
044 *          <jk>return</jk> req;
045 *       }
046 *    }
047 * </p>
048 * 
049 * <p>
050 * Converters can also be associated at the servlet level using the {@link RestResource#converters() @RestResource.converters()} annotation.
051 * <br>Applying converters at the resource level is equivalent to applying converters to each resource method individually.
052 * 
053 * <h5 class='topic'>How to implement</h5>
054 * 
055 * Implementers should simply implement the {@link #convert(RestRequest, Object)} and return back a 'converted' object.
056 * <br>It's up to the implementer to decide what this means.
057 * 
058 * <p>
059 * Subclasses must implement one of the following constructors:
060 * <ul>
061 *    <li><jk>public</jk> T();  <jc>// No-arg constructor</jc>
062 *    <li><jk>public</jk> T(PropertyStore);  <jc>// Property store of the RestContext</jc>
063 * </ul>
064 * 
065 * <p>
066 * Subclasses can also be defined as inner classes of the resource class.
067 * 
068 * <h5 class='topic'>Predefined converters</h5>
069 * <ul>
070 *    <li class='jc'>{@link Traversable} - Allows URL additional path info to address individual elements in a POJO tree.
071 *    <li class='jc'>{@link Queryable} - Allows query/view/sort functions to be performed on POJOs.
072 *    <li class='jc'>{@link Introspectable} - Allows Java public methods to be invoked on the returned POJOs.
073 * </ul>
074 * 
075 * <h5 class='section'>See Also:</h5>
076 * <ul>
077 *    <li class='jf'>{@link RestContext#REST_converters} - Registering converters with REST resources.
078 *    <li class='link'><a class="doclink" href="../../../../overview-summary.html#juneau-rest-server.Converters">Overview &gt; juneau-rest-server &gt; Converters</a>
079 * </ul>
080 */
081public interface RestConverter {
082
083   /**
084    * Performs post-call conversion on the specified response object.
085    * 
086    * @param req The servlet request.
087    * @param res The response object set by the REST method through the {@link RestResponse#setOutput(Object)} method.
088    * @return The converted object.
089    * @throws RestException Thrown if any errors occur during conversion.
090    * @throws SerializeException
091    */
092   public Object convert(RestRequest req, Object res) throws RestException, SerializeException;
093}