juneau-doc/docs/Topics/06.juneau-rest-server/21.Converters.html

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Converters

<p>
	Converters can be thought of as "post-processors" for POJOs before they get passed to the serializers.
</p>
<p>
	Converters are associated with resource classes and methods via the following:
</p>
<ul class='javatree'>
	<li class='ja'>{@link oajr.annotation.Rest#converters() Rest(converters)} 
	<li class='ja'>{@link oajr.annotation.RestMethod#converters() RestMethod(converters)} 
	<li class='jm'>{@link oajr.RestContextBuilder#converters(Class...)} 
</ul>
<h5 class='figure'>Example:</h5>
<p class='bpcode w800'>
	<jc>// Associate the Traversable converter to all Java REST methods in this servlet</jc>
	<ja>@Rest</ja>(converters=Traversable.<jk>class</jk>)
	<jk>public</jk> MyRestServlet <jk>extends</jk> BasicRestServlet {
		...
	}
</p>
<p>
	They can also be defined at the method level:
</p>
<p class='bpcode w800'>
	<jc>// GET person request handler.</jc>
	<jc>// Traversable conversion enabled to allow nodes in returned POJO tree to be addressed.</jc>
	<jc>// Queryable conversion enabled to allow returned POJO to be searched/viewed/sorted.</jc>
	<ja>@RestMethod</ja>(
		name=<jsf>GET</jsf>, path=<js>"/people/{id}/*"</js>,
		converters={Traversable.<jk>class</jk>,Queryable.<jk>class</jk>}
	)
	<jk>public</jk> Person getPerson(<ja>@Path</ja>(<js>"id"</js>) <jk>int</jk> id) {
		<jk>return</jk> findPerson(id);
	}
</p>	
<p>
	The following converter is used to provide support for addressing child nodes in a POJO tree with URL path 
	remainders.  
	In this code, the 3rd parameter is the object that was returned by the Java method.
	The converter uses the {@link oaj.utils.PojoRest} wrapper class to address nodes in the 
	tree.
</p>
<p class='bpcode w800'>
	<jd>/**
	 * Converter for enablement of PojoRest support on response objects returned by a @RestMethod method.
	 * When enabled, objects in a POJO tree returned by the REST method can be addressed through additional URL path information.
	 */</jd>
	<jk>public class</jk> Traversable <jk>implements</jk> RestConverter {
	
		<ja>@Override</ja> <jc>/* RestConverter */</jc>
		<jk>public</jk> Object convert(RestRequest req, Object o) <jk>throws</jk> RestException {
			if (o == <jk>null</jk>)
				<jk>return null</jk>;
	
			String pathRemainder = req.getPathMatch().getRemainder();
	
			<jk>if</jk> (pathRemainder != <jk>null</jk>) {
				<jk>try</jk> {
				
					<jc>// Use the PojoRest class to traverse our POJO model.</jc> 
					PojoRest p = <jk>new</jk> PojoRest(o);
					o = p.get(pathRemainder);
				
				} <jk>catch</jk> (PojoRestException e) {
					<jk>throw new</jk> RestException(e.getStatus(), e);
				} <jk>catch</jk> (Exception e) {
					<jk>throw new</jk> RestException(HttpServletResponse.<jsf>SC_INTERNAL_SERVER_ERROR</jsf>, e);
				}
			}
			
			<jk>return</jk> o;
		}
	}
</p>	
<p>
	Juneau defines the following converters out-of-the-box:
</p>
<ul class='javatree'>
	<li class='jic'>
	{@link oajr.RestConverter}
	<ul>
		<li class='jc'>
			{@link oajr.converters.Queryable}
			<br>Provides query parameters that can be used to transform the response (i.e. search/view/sort the 
			POJO response before being serialized).
		<li class='jc'>
			{@link oajr.converters.Traversable}
			<br>Allows nodes in the POJO response tree to be individually accessed through additional path info on 
			the request.
		<li class='jc'>
			{@link oajr.converters.Introspectable}
			<br>Allows method calls to be made on the response POJO, and for the result of that method call to be 
			serialized as the response.
	</ul>
</ul>

<ul class='seealso'>
	<li class='jf'>{@link oajr.RestContext#REST_converters} 
</ul>