juneau-doc/docs/Topics/02.juneau-marshall/11.Transforms/08.SurrogateClasses.html

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Surrogate Classes

<p>
<p>
	Surrogate classes are very similar in concept to <c>PojoSwaps</c> except they're simpler to define.
</p>
<p>
	For example, let's say we want to be able to serialize the following class, but it's not serializable for 
	some reason (for example, there are no properties exposed):  
<p class='bpcode w800'>
	<jc>// Not serializable because it's not a bean because it has no public properties.</jc>
	<jk>public class</jk> MyNonSerializableClass {
		<jk>protected</jk> String <jf>foo</jf>;
	}
</p>
<p>
	This could be solved with the following <c>PojoSwap</c>.
</p>
<p class='bpcode w800'>
	<jc>// A serializable bean with 1 property.</jc>
	<jk>public class</jk> MySerializableSurrogate {
		<jk>public</jk> String <jf>foo</jf>;
	}
		
	<jc>// A PojoSwap that swaps out our non-serializable object with our serializable object.</jc>
	<jk>public class</jk> MySwap <jk>extends</jk> PojoSwap&lt;MyNonSerializableClass,MySerializableSurrogate&gt; {
		<ja>@Override</ja> <jc>/* PojoSwap */</jc>
		<jk>public</jk> MySerializableSurrogate swap(MyNonSerializableClass o) {
			
			<jc>// Create some serializable class and manually copy the data into it.</jc>
			MySerializableSurrogate s = <jk>new</jk> MySerializableSurrogate();
			s.<jf>foo</jf> = o.<jf>foo</jf>;
			<jk>return</jk> s;
		}
	}
</p>
<p>
	However, the same can be accomplished by using a surrogate class that simply contains a constructor with 
	the non-serializable class as an argument:
</p>
<p class='bpcode w800'>
	<jk>public class</jk> MySerializableSurrogate {
		<jk>public</jk> String <jf>foo</jf>;
		
		<jc>// Constructor takes in our non-serializable object!</jc>
		<jk>public</jk> MySerializableSurrogate(MyNonSerializableClass c) {
			<jk>this</jk>.<jf>foo</jf> = c.<jf>foo</jf>;
		}
	}
</p>
<p>
	The surrogate class is registered in the same way as a <c>PojoSwap</c>:
</p>
<p class='bpcode w800'>
	<jc>// Create a JSON serializer that can serialize Iterators.</jc>
	WriterSerializer s = JsonSerializer.<jsm>create</jsm>().pojoSwaps(MySerializableSurrogate.<jk>class</jk>).build();
</p>
<p>
	When the serializer encounters the non-serializable class, it will serialize an instance of the surrogate 
	instead.
</p>

<ul class='seealso'>
	<li class='jic'>{@link oaj.transform.Surrogate}
</ul>