juneau-doc/docs/Topics/02.juneau-marshall/11.Transforms/06.SwapAnnotation.html

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@Swap Annotation

<p>
	{@link oaj.annotation.Swap @Swap} can be used to associate a swap class using an 
	annotation.
	This is often cleaner than using the builder <c>pojoSwaps()</c> method since you can keep
	your swap class near your POJO class. 
</p>
<p class='bpcode w800'>
	<ja>@Swap</ja>(MyPojoSwap.<jk>class</jk>)
	<jk>public class</jk> MyPojo {
		...
	}
	
	<jc>// Sample swap for converting MyPojo classes to a simple string.</jc>
	<jk>public class</jk> MyPojoSwap <jk>extends</jk> PojoSwap&lt;MyPojo,String&gt; {
		
		<ja>@Override</ja> <jc>/* PojoSwap */</jc>
		<jk>public</jk> String swap(BeanSession session, MyPojo o) {
			<jk>return</jk> o.toSomeSerializableForm();
		}
	}
</p>
<p>
	Multiple swaps can be associated with a POJO by using the {@link oaj.annotation.Swaps @Swaps} annotation:
</p>
<p class='bpcode w800'>
	<ja>@Swaps</ja>(
		{
			<ja>@Swap</ja>(MyJsonSwap.<jk>class</jk>),
			<ja>@Swap</ja>(MyXmlSwap.<jk>class</jk>),
			<ja>@Swap</ja>(MyOtherSwap.<jk>class</jk>)
		}
	)
	<jk>public class</jk> MyPojo {}
</p>
<p>
	<c>Readers</c> get serialized directly to the output of a serializer.
	Therefore it's possible to implement a swap that provides fully-customized output.
</p>
<p class='bpcode w800'>
	<jk>public class</jk> MyJsonSwap <jk>extends</jk> PojoSwap&lt;MyPojo,Reader&gt; {

		<jk>public</jk> MediaType[] forMediaTypes() {
			<jk>return</jk> MediaType.<jsm>forStrings</jsm>(<js>"&#42;/json"</js>);
		}

		<jk>public</jk> Reader swap(BeanSession session, MyPojo o) <jk>throws</jk> Exception {
			<jk>return new</jk> StringReader(<js>"{message:'Custom JSON!'}"</js>);
		}
	}
</p>
<p>
	The <ja>@Swap</ja> annotation can also be used on getters and setters as well to apply a swap
	to individual property values:
</p>
<p class='bpcode w800'>
	<jk>public class</jk> MyBean {
		<jk>private</jk> MyPojo <jf>myPojo</jf>;
	
		<jc>// Swap applied to bean property.	
		<ja>@Beanp</ja>(swap=MyPojoSwap.<jk>class</jk>)
		<jk>public</jk> MyPojo getMyPojo() {
			<jk>return</jk> <jf>myPojo</jf>;
		}
	}
</p>
<p>
	When applied to bean properties, the swap annotation need only be applied to either the getter, setter, or field.
</p>
<p>
	The swap annotation can also be applied to the private field of a bean property, like so:
</p>
<p class='bpcode w800'>
	<jk>public class</jk> MyBean {

		<ja>@Beanp</ja>(swap=MyPojoSwap.<jk>class</jk>)
		<jk>private</jk> MyPojo <jf>myPojo</jf>;
	
		<jk>public</jk> MyPojo getMyPojo() {
			<jk>return</jk> <jf>myPojo</jf>;
		}
		
		<jk>public</jk> MyBean setMyPojo(MyPojo myPojo) {
			<jk>this</jk>.<jf>myPojo</jf> = myPojo;
			<jk>return this</jk>;
		}
	}
</p>