tutorials/composites/src/main/java/org/apache/zest/tutorials/composites/tutorial8/package.html - polygene-java - Git at Google

 <!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 -->
 <body>
 <h1>Tutorial 8 - Generic mixins</h1>
 <p>
 In this tutorial we will look at how to use generic Fragments. So far all Fragments, i.e.
 the Concerns, SideEffects, and Mixins, have directly implemented the domain interface. But sometimes it is
 useful to be able to provide a generic implementation of an interface. An example of this is
 the HelloWorldState interface. Since it only handles properties, and the old version used the JavaBean rules
 for naming getters and setters we could create a mixin that handles invocations of such methods
 automatically for us by storing the properties in a map and use the methods
 to look them up.
 </p>
 <p>
 Implementing a generic Fragment is done by creating a class that implements the interface
 java.lang.proxy.InvocationHandler. This has a single "invoke" method which is passed the
 object that was invoked (the TransientComposite in this case), the method, and the arguments. The
 Fragment is then allowed to implement the method any way it wants.
 </p>
 <p>
 Since interfaces with only Properties is such a common case Zest™ already has a generic Mixin
 that implements the Properties management described above, but for the builtin Property type instead
 of the getter/setter variant. The class is aptly named PropertyMixin.
 </p>
 <p>
 While we could use it, for now we will implement it ourselves to get a feel for how generic Mixins work.
 </p>
 <p>
 Steps for this tutorial:
 </p>
 <ol>
     <li>Remove the HelloWorldStateMixin</li>
     <li>Add a GenericPropertyMixin, and have it implement InvocationHandler</li>
     <li>Inject "@State StateHolder state" in the mixin. The StateHolder interface will give
         you access to the Properties for the TransientComposite which Zest™ manages for you
     </li>
     <li>On call to invoke(), delegate to the StateHolder interface to get the Property for the invoked method</li>
     <li>Add an @AppliesTo annotation to the Mixin and implement the AppliesToFilter with a rule that
         matches only methods that return Property values.
     </li>
     <li>Add the mixin to the TransientComposite.</li>
 </ol>
 </body>
	<!--
	Licensed to the Apache Software Foundation (ASF) under one or more
	contributor license agreements. See the NOTICE file distributed with
	this work for additional information regarding copyright ownership.
	The ASF licenses this file to You under the Apache License, Version 2.0
	(the "License"); you may not use this file except in compliance with
	the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->
	<body>
	<h1>Tutorial 8 - Generic mixins</h1>
	<p>
	In this tutorial we will look at how to use generic Fragments. So far all Fragments, i.e.
	the Concerns, SideEffects, and Mixins, have directly implemented the domain interface. But sometimes it is
	useful to be able to provide a generic implementation of an interface. An example of this is
	the HelloWorldState interface. Since it only handles properties, and the old version used the JavaBean rules
	for naming getters and setters we could create a mixin that handles invocations of such methods
	automatically for us by storing the properties in a map and use the methods
	to look them up.
	</p>
	<p>
	Implementing a generic Fragment is done by creating a class that implements the interface
	java.lang.proxy.InvocationHandler. This has a single "invoke" method which is passed the
	object that was invoked (the TransientComposite in this case), the method, and the arguments. The
	Fragment is then allowed to implement the method any way it wants.
	</p>
	<p>
	Since interfaces with only Properties is such a common case Zest™ already has a generic Mixin
	that implements the Properties management described above, but for the builtin Property type instead
	of the getter/setter variant. The class is aptly named PropertyMixin.
	</p>
	<p>
	While we could use it, for now we will implement it ourselves to get a feel for how generic Mixins work.
	</p>
	<p>
	Steps for this tutorial:
	</p>
	<ol>
	<li>Remove the HelloWorldStateMixin</li>
	<li>Add a GenericPropertyMixin, and have it implement InvocationHandler</li>
	<li>Inject "@State StateHolder state" in the mixin. The StateHolder interface will give
	you access to the Properties for the TransientComposite which Zest™ manages for you
	</li>
	<li>On call to invoke(), delegate to the StateHolder interface to get the Property for the invoked method</li>
	<li>Add an @AppliesTo annotation to the Mixin and implement the AppliesToFilter with a rule that
	matches only methods that return Property values.
	</li>
	<li>Add the mixin to the TransientComposite.</li>
	</ol>
	</body>