juneau-doc/docs/Topics/02.juneau-marshall/12.Transforms/19.BypassSerialization.html

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Bypass Serialization using Readers and InputStreams

<p>
	Juneau serializers treat instances of <c>Readers</c> and <c>InputStreams</c> special by 
	simply serializing their contents directly to the output stream or writer.
	This allows you to embed fully customized serializer output.
</p>
<p class='bpcode w800'>
	<jk>public class</jk> MyBean {
		<jc>// A bean property that produces raw JSON.</jc>
		<jk>public</jk> Reader f1 = <jk>new</jk> StringReader(<js>"{'foo':'bar'}"</js>);	
	}	
	
	<jc>// Produces "{f1:{'foo':'bar'}}"</jc>
	String json = SimpleJsonSerializer.<jsf>DEFAULT</jsf>
.toString(<jk>new</jk> MyBean());
</p>			
<p>
	Note that if you're serializing Readers and InputStreams, it's up to you to make sure you're producing
	valid output (in this case JSON).
</p>
<p>
	A more typical scenario where this is useful is by using swaps to convert POJOs to Readers whose 
	contents are determined via the {@link oaj.BeanSession#getMediaType()} method.
	In the following example, we're customizing the JSON output for a particular bean type, but leaving
	all other renditions as-is:
</p>			
<p class='bpcode w800'>
	<ja>@Swap</ja>(MyBeanSwapSometimes.<jk>class</jk>)
	<jk>public class</jk> MyBean {...}
	
	<jc>// A swap that produces specialized output for JSON, but default serialization for</jc>
	<jc>// all other media types.</jc>
	<jk>public class</jk> MyBeanSwapSometimes <jk>extends</jk> PojoSwap&lt;MyBean,Object&gt; {
		<jk>public</jk> Object swap(BeanSession session, MyPojo o) <jk>throws</jk> Exception {
			MediaType mt = session.getMediaType();
			<jk>if</jk> (mt.hasSubType(<js>"json"</js>))
				<jk>return new</jk> StringReader(<js>"{myPojo:'foobar'}"</js>);  <jc>// Custom JSON output</jc>
			<jk>return</jk> o;  <jc>// Otherwise serialize it as a normal bean</jc>
		}
	}
</p>	
<div class='info'>
	Due to the nature of the RDF serializers, Readers and InputStreams are serialized as literals,
	not as RDF text.
	This is due to the fact that the RDF serializers use a DOM for serialization, so we don't have
	access to the underlying stream.
</div>