legacy-tests/build/test/4/pgui_datamodel_objectWrapper.html - freemarker-docgen - Git at Google

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 <div class="col-right"><div class="page-content"><div class="page-title"><div class="pagers top"><a class="paging-arrow previous" href="pgui_datamodel_node.html"><span>Previous</span></a><a class="paging-arrow next" href="pgui_config.html"><span>Next</span></a></div><div class="title-wrapper">
 <h1 class="content-header header-section1" id="pgui_datamodel_objectWrapper" itemprop="headline">Object wrappers</h1>
 </div></div><p>When you add something to a container, it may receive any java
         object as a parameter, not necessarily a
         <code class="inline-code">TemplateModel</code>, as you could see in the FreeMarker
         API. This is because the container implementation can silently replace
         that object with the appropriate <code class="inline-code">TemplateModel</code>
         object. For example if you add a <code class="inline-code">String</code> to the
         container, perhaps it will be replaced with a
         <code class="inline-code">SimpleScalar</code> instance which stores the same
         text.</p><p>As for when the replacement occurs, it&#39;s the business of the
         container in question (i.e. the business of the class that implements
         the container interface), but it must happen at the latest when you
         get the subvariable, as the getter methods (according to the
         interfaces) return <code class="inline-code">TemplateModel</code>, not
         <code class="inline-code">Object</code>. For example, <code class="inline-code">SimpleHash</code>,
         <code class="inline-code">SimpleSequence</code> and
         <code class="inline-code">SimpleCollection</code> use the laziest strategy; they
         replace a non-<code class="inline-code">TemplateModel</code> subvariable with an
         appropriate <code class="inline-code">TemplateModel</code> object when you get the
         subvariable for the first time.</p><p>As for what java objects can be replaced, and with what
         <code class="inline-code">TemplateModel</code> implementations, it is either handled
         by the container implementation itself, or it delegates this to an
         <code class="inline-code">ObjectWrapper</code> instance.
         <code class="inline-code">ObjectWrapper</code> is an interface that specifies one
         method: <code class="inline-code">TemplateModel wrap(java.lang.Object obj)</code>.
         You pass in an <code class="inline-code">Object</code>, and it returns the
         corresponding <code class="inline-code">TemplateModel</code> object, or throws a
         <code class="inline-code">TemplateModelException</code> if this is not possible. The
         replacement rules are coded into the <code class="inline-code">ObjectWrapper</code>
         implementation.</p><p>The most important <code class="inline-code">ObjectWrapper</code>
         implementations that the FreeMarker core provides are:</p><ul>
           <li>
             <p><code class="inline-code">ObjectWrapper.DEFAULT_WRAPPER</code>: It
             replaces <code class="inline-code">String</code> with
             <code class="inline-code">SimpleScalar</code>, <code class="inline-code">Number</code> with
             <code class="inline-code">SimpleNumber</code>, <code class="inline-code">List</code> and array
             with <code class="inline-code">SimpleSequence</code>, <code class="inline-code">Map</code>
             with <code class="inline-code">SimpleHash</code>, <code class="inline-code">Boolean</code>
             with <code class="inline-code">TemplateBooleanModel.TRUE</code> or
             <code class="inline-code">TemplateBooleanModel.FALSE</code>, W3C DOM nodes with
             <code class="inline-code">freemarker.ext.dom.NodeModel</code>. For Jython
             objects, this wrapper will invoke
             <code class="inline-code">freemarker.ext.jython.JythonWrapper</code>. For all
             other objects, it will invoke <a href="pgui_misc_beanwrapper.html"><code>BEANS_WRAPPER</code></a>.</p>
           </li>

           <li>
             <p><code class="inline-code">ObjectWrapper.BEANS_WRAPPER</code>: It can
             expose java Bean properties and other members of arbitrary objects
             using Java reflection. At least in FreeMarker 2.3, it is a
             <code class="inline-code">freemarker.ext.beans.BeansWrapper</code> instance;
             there is a separated <a href="pgui_misc_beanwrapper.html">chapter
             about it</a>.</p>
           </li>
         </ul><p>For a concrete example, let&#39;s see how the
         <code class="inline-code">Simple<em class="code-color">Xxx</em></code> classes work.
         <code class="inline-code">SimpleHash</code>, <code class="inline-code">SimpleSequence</code> and
         <code class="inline-code">SimpleCollection</code> use
         <code class="inline-code">DEFAULT_WRAPPER</code> to wrap the subvariables (unless
         you pass in an alternative wrapper in their constructor). So this
         example demonstrates <code class="inline-code">DEFAULT_WRAPPER</code> in
         action:</p>

 <div class="code-wrapper"><pre class="code-block code-unspecified">Map map = new HashMap();
 map.put(&quot;anotherString&quot;, &quot;blah&quot;);
 map.put(&quot;anotherNumber&quot;, new Double(3.14));
 List list = new ArrayList();
 list.add(&quot;red&quot;);
 list.add(&quot;green&quot;);
 list.add(&quot;blue&quot;);

 SimpleHash root = new SimpleHash();  // will use the default wrapper
 root.put(&quot;theString&quot;, &quot;wombat&quot;);
 root.put(&quot;theNumber&quot;, new Integer(8));
 root.put(&quot;theMap&quot;, map);
 root.put(&quot;theList&quot;, list);</pre></div><p>Assuming that root is the data-model root, the resulting
         data-model is:</p>

 <div class="code-wrapper"><pre class="code-block code-data-model">(root)
  |
  +- theString = &quot;wombat&quot;
  |
  +- theNumber = 8
  |
  +- theMap
  |   |
  |   +- anotherString = &quot;blah&quot;
  |   |
  |   +- anotherNumber = 3.14
  |
  +- theList
      |
      +- (1st) = &quot;red&quot;
      |
      +- (2nd) = &quot;green&quot;
      |
      +- (3rd) = &quot;blue&quot;</pre></div><p>Note that the <code class="inline-code">Object</code>-s inside
         <code class="inline-code">theMap</code> and <code class="inline-code">theList</code> are
         accessible as subvariables too. This is because when you, say, try to
         access <code class="inline-code">theMap.anotherString</code>, then the
         <code class="inline-code">SimpleHash</code> (which is used as root hash here) will
         silently replace the <code class="inline-code">Map</code>
         (<code class="inline-code">theMap</code>) with a <code class="inline-code">SimpleHash</code>
         instance that uses the same wrapper as the root hash, so when you try
         to access the <code class="inline-code">anotherString</code> subvariable of it, it
         will replace that with a <code class="inline-code">SimpleScalar</code>.</p><p>If you drop an ``arbitrary&#39;&#39; object into the data-model,
         <code class="inline-code">DEFAULT_WRAPPER</code> will invoke
         <code class="inline-code">BEANS_WRAPPER</code> to wrap the object:</p>

 <div class="code-wrapper"><pre class="code-block code-unspecified">SimpleHash root = new SimpleHash();
 // expose a &quot;simple&quot; java objects:
 root.put(&quot;theString&quot;, &quot;wombat&quot;);
 // expose an &quot;arbitrary&quot; java objects:
 root.put(&quot;theObject&quot;, new TestObject(&quot;green mouse&quot;, 1200));</pre></div><p>Assuming this is <code class="inline-code">TestObject</code>:</p>

 <div class="code-wrapper"><pre class="code-block code-unspecified">public class TestObject {
     private String name;
     private int price;

     public TestObject(String name, int price) {
         this.name = name;
         this.price = price;
     }

     // JavaBean properties
     // Note that public fields are not visible directly;
     // you must write a getter method for them.
     public String getName() {return name;}
     public int getPrice() {return price;}

     // A method
     public double sin(double x) {
         return Math.sin(x);
     }
 }</pre></div><p>The data-model will be:</p>

 <div class="code-wrapper"><pre class="code-block code-data-model">(root)
  |
  +- theString = &quot;wombat&quot;
  |
  +- theObject
      |
      +- name = &quot;green mouse&quot;
      |
      +- price = 1200
      |
      +- number sin(number)</pre></div><p>So we can merge it with this template:</p>

 <div class="code-wrapper"><pre class="code-block code-template">${theObject.name}
 ${theObject.price}
 ${theObject.sin(123)}</pre></div><p>Which will output:</p>

 <div class="code-wrapper"><pre class="code-block code-output">green mouse
 1200
 -0,45990349068959124</pre></div><p>You have seen in earlier examples of this manual that we have
         used <code class="inline-code">java.util.HashMap</code> as root hash, and not
         <code class="inline-code">SimpleHash</code> or other FreeMarker specific class. It
         works because
         <code class="inline-code">Template.process(<em class="code-color">...</em>)</code>
         automatically wraps the object you give as its data-model argument. It
         uses the object wrapper dictated by the
         <code class="inline-code">Configuration</code> level <a href="pgui_config_settings.html">setting</a>,
         <code class="inline-code">object_wrapper</code> (unless you explicitly specify an
         <code class="inline-code">ObjectWrapper</code> as its parameter). Thus, in simple
         FreeMarker application you need not know about
         <code class="inline-code">TemplateModel</code>-s at all. Note that the root need not
         be a <code class="inline-code">java.util.Map</code>. It can be anything that is
         wrapped so that it implements the <code class="inline-code">TemplateHashModel</code>
         interface.</p><p>The factory default value of the
         <code class="inline-code">object_wrapper</code> setting is
         <code class="inline-code">ObjectWrapper.DEFAULT_WRAPPER</code>. If you want to
         change it to, say, <code class="inline-code">ObjectWrapper.BEANS_WRAPPER</code>, you
         can configure the FreeMarker engine (before starting to use it from
         other threads) like this:</p>

 <div class="code-wrapper"><pre class="code-block code-unspecified">cfg.setObjectWrapper(ObjectWrapper.BEANS_WRAPPER);</pre></div><p>Note that you can set any object here that implements interface
         <code class="inline-code">ObjectWrapper</code>, so you can set your custom
         implementation as well.</p><p>For <code class="inline-code">TemplateModel</code> implementations that wrap
         basic Java container types, as <code class="inline-code">java.util.Map</code>-s and
         <code class="inline-code">java.util.List</code>-s, the convention is that they use
         the same object wrapper to wrap their subvariables as their parent
         container does. Technically correctly said, they are instantiated by
         their parent container (so it has full control over the creation of
         them), and the parent container create them so they will use the same
         object wrapper as the parent itself. Thus, if
         <code class="inline-code">BEANS_WRAPPER</code> is used for the wrapping of the root
         hash, it will be used for the wrapping of the subvariables (and the
         subvariables of the subvariables, etc.) as well. This is exactly the
         same phenomenon as you have seen with
         <code class="inline-code">theMap.anotherString</code> earlier.</p><div class="bottom-pagers-wrapper"><div class="pagers bottom"><a class="paging-arrow previous" href="pgui_datamodel_node.html"><span>Previous</span></a><a class="paging-arrow next" href="pgui_config.html"><span>Next</span></a></div></div></div></div>      </div>
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	<!--[if lte IE 9]>
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	<![endif]--><div class="header-top-bg"><div class="site-width header-top"><a class="logo" href="http://example.com" role="banner"> <img itemprop="image" src="logo.png" alt="My Logo">
	</a></div></div><div class="header-bottom-bg"><div class="site-width search-row"><a href="index.html" class="navigation-header">FreeMarker Manual</a><div class="navigation-header"></div></div><div class="site-width breadcrumb-row"><ul class="breadcrumb" itemscope itemtype="http://schema.org/BreadcrumbList"><li class="step-0" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="index.html"><span itemprop="name">FreeMarker Manual</span></a></li><li class="step-1" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="pgui.html"><span itemprop="name">Programmer's Guide</span></a></li><li class="step-2" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="pgui_datamodel.html"><span itemprop="name">The Data Model</span></a></li><li class="step-3" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="pgui_datamodel_objectWrapper.html"><span itemprop="name">Object wrappers</span></a></li></ul><div class="bookmarks" title="Bookmarks"><span class="sr-only">Bookmarks:</span><ul class="bookmark-list"><li><a href="alphaidx.html">Index</a></li><li><a href="gloss.html">Glossary</a></li><li><a href="ref.html">Reference</a></li><li><a href="app_faq.html">FAQ</a></li><li><a href="preface.html#test_target">Bőregér</a></li></ul></div></div></div> <div class="main-content site-width">
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	<div class="col-right"><div class="page-content"><div class="page-title"><div class="pagers top"><a class="paging-arrow previous" href="pgui_datamodel_node.html"><span>Previous</span></a><a class="paging-arrow next" href="pgui_config.html"><span>Next</span></a></div><div class="title-wrapper">
	<h1 class="content-header header-section1" id="pgui_datamodel_objectWrapper" itemprop="headline">Object wrappers</h1>
	</div></div><p>When you add something to a container, it may receive any java
	object as a parameter, not necessarily a
	<code class="inline-code">TemplateModel</code>, as you could see in the FreeMarker
	API. This is because the container implementation can silently replace
	that object with the appropriate <code class="inline-code">TemplateModel</code>
	object. For example if you add a <code class="inline-code">String</code> to the
	container, perhaps it will be replaced with a
	<code class="inline-code">SimpleScalar</code> instance which stores the same
	text.</p><p>As for when the replacement occurs, it's the business of the
	container in question (i.e. the business of the class that implements
	the container interface), but it must happen at the latest when you
	get the subvariable, as the getter methods (according to the
	interfaces) return <code class="inline-code">TemplateModel</code>, not
	<code class="inline-code">Object</code>. For example, <code class="inline-code">SimpleHash</code>,
	<code class="inline-code">SimpleSequence</code> and
	<code class="inline-code">SimpleCollection</code> use the laziest strategy; they
	replace a non-<code class="inline-code">TemplateModel</code> subvariable with an
	appropriate <code class="inline-code">TemplateModel</code> object when you get the
	subvariable for the first time.</p><p>As for what java objects can be replaced, and with what
	<code class="inline-code">TemplateModel</code> implementations, it is either handled
	by the container implementation itself, or it delegates this to an
	<code class="inline-code">ObjectWrapper</code> instance.
	<code class="inline-code">ObjectWrapper</code> is an interface that specifies one
	method: <code class="inline-code">TemplateModel wrap(java.lang.Object obj)</code>.
	You pass in an <code class="inline-code">Object</code>, and it returns the
	corresponding <code class="inline-code">TemplateModel</code> object, or throws a
	<code class="inline-code">TemplateModelException</code> if this is not possible. The
	replacement rules are coded into the <code class="inline-code">ObjectWrapper</code>
	implementation.</p><p>The most important <code class="inline-code">ObjectWrapper</code>
	implementations that the FreeMarker core provides are:</p><ul>
	<li>
	<p><code class="inline-code">ObjectWrapper.DEFAULT_WRAPPER</code>: It
	replaces <code class="inline-code">String</code> with
	<code class="inline-code">SimpleScalar</code>, <code class="inline-code">Number</code> with
	<code class="inline-code">SimpleNumber</code>, <code class="inline-code">List</code> and array
	with <code class="inline-code">SimpleSequence</code>, <code class="inline-code">Map</code>
	with <code class="inline-code">SimpleHash</code>, <code class="inline-code">Boolean</code>
	with <code class="inline-code">TemplateBooleanModel.TRUE</code> or
	<code class="inline-code">TemplateBooleanModel.FALSE</code>, W3C DOM nodes with
	<code class="inline-code">freemarker.ext.dom.NodeModel</code>. For Jython
	objects, this wrapper will invoke
	<code class="inline-code">freemarker.ext.jython.JythonWrapper</code>. For all
	other objects, it will invoke <a href="pgui_misc_beanwrapper.html"><code>BEANS_WRAPPER</code></a>.</p>
	</li>

	<li>
	<p><code class="inline-code">ObjectWrapper.BEANS_WRAPPER</code>: It can
	expose java Bean properties and other members of arbitrary objects
	using Java reflection. At least in FreeMarker 2.3, it is a
	<code class="inline-code">freemarker.ext.beans.BeansWrapper</code> instance;
	there is a separated <a href="pgui_misc_beanwrapper.html">chapter
	about it</a>.</p>
	</li>
	</ul><p>For a concrete example, let's see how the
	<code class="inline-code">Simple<em class="code-color">Xxx</em></code> classes work.
	<code class="inline-code">SimpleHash</code>, <code class="inline-code">SimpleSequence</code> and
	<code class="inline-code">SimpleCollection</code> use
	<code class="inline-code">DEFAULT_WRAPPER</code> to wrap the subvariables (unless
	you pass in an alternative wrapper in their constructor). So this
	example demonstrates <code class="inline-code">DEFAULT_WRAPPER</code> in
	action:</p>

	<div class="code-wrapper"><pre class="code-block code-unspecified">Map map = new HashMap();
	map.put("anotherString", "blah");
	map.put("anotherNumber", new Double(3.14));
	List list = new ArrayList();
	list.add("red");
	list.add("green");
	list.add("blue");

	SimpleHash root = new SimpleHash(); // will use the default wrapper
	root.put("theString", "wombat");
	root.put("theNumber", new Integer(8));
	root.put("theMap", map);
	root.put("theList", list);</pre></div><p>Assuming that root is the data-model root, the resulting
	data-model is:</p>

	<div class="code-wrapper"><pre class="code-block code-data-model">(root)
	\|
	+- theString = "wombat"
	\|
	+- theNumber = 8
	\|
	+- theMap
	\| \|
	\| +- anotherString = "blah"
	\| \|
	\| +- anotherNumber = 3.14
	\|
	+- theList
	\|
	+- (1st) = "red"
	\|
	+- (2nd) = "green"
	\|
	+- (3rd) = "blue"</pre></div><p>Note that the <code class="inline-code">Object</code>-s inside
	<code class="inline-code">theMap</code> and <code class="inline-code">theList</code> are
	accessible as subvariables too. This is because when you, say, try to
	access <code class="inline-code">theMap.anotherString</code>, then the
	<code class="inline-code">SimpleHash</code> (which is used as root hash here) will
	silently replace the <code class="inline-code">Map</code>
	(<code class="inline-code">theMap</code>) with a <code class="inline-code">SimpleHash</code>
	instance that uses the same wrapper as the root hash, so when you try
	to access the <code class="inline-code">anotherString</code> subvariable of it, it
	will replace that with a <code class="inline-code">SimpleScalar</code>.</p><p>If you drop an ``arbitrary'' object into the data-model,
	<code class="inline-code">DEFAULT_WRAPPER</code> will invoke
	<code class="inline-code">BEANS_WRAPPER</code> to wrap the object:</p>

	<div class="code-wrapper"><pre class="code-block code-unspecified">SimpleHash root = new SimpleHash();
	// expose a "simple" java objects:
	root.put("theString", "wombat");
	// expose an "arbitrary" java objects:
	root.put("theObject", new TestObject("green mouse", 1200));</pre></div><p>Assuming this is <code class="inline-code">TestObject</code>:</p>

	<div class="code-wrapper"><pre class="code-block code-unspecified">public class TestObject {
	private String name;
	private int price;

	public TestObject(String name, int price) {
	this.name = name;
	this.price = price;
	}

	// JavaBean properties
	// Note that public fields are not visible directly;
	// you must write a getter method for them.
	public String getName() {return name;}
	public int getPrice() {return price;}

	// A method
	public double sin(double x) {
	return Math.sin(x);
	}
	}</pre></div><p>The data-model will be:</p>

	<div class="code-wrapper"><pre class="code-block code-data-model">(root)
	\|
	+- theString = "wombat"
	\|
	+- theObject
	\|
	+- name = "green mouse"
	\|
	+- price = 1200
	\|
	+- number sin(number)</pre></div><p>So we can merge it with this template:</p>

	<div class="code-wrapper"><pre class="code-block code-template">${theObject.name}
	${theObject.price}
	${theObject.sin(123)}</pre></div><p>Which will output:</p>

	<div class="code-wrapper"><pre class="code-block code-output">green mouse
	1200
	-0,45990349068959124</pre></div><p>You have seen in earlier examples of this manual that we have
	used <code class="inline-code">java.util.HashMap</code> as root hash, and not
	<code class="inline-code">SimpleHash</code> or other FreeMarker specific class. It
	works because
	<code class="inline-code">Template.process(<em class="code-color">...</em>)</code>
	automatically wraps the object you give as its data-model argument. It
	uses the object wrapper dictated by the
	<code class="inline-code">Configuration</code> level <a href="pgui_config_settings.html">setting</a>,
	<code class="inline-code">object_wrapper</code> (unless you explicitly specify an
	<code class="inline-code">ObjectWrapper</code> as its parameter). Thus, in simple
	FreeMarker application you need not know about
	<code class="inline-code">TemplateModel</code>-s at all. Note that the root need not
	be a <code class="inline-code">java.util.Map</code>. It can be anything that is
	wrapped so that it implements the <code class="inline-code">TemplateHashModel</code>
	interface.</p><p>The factory default value of the
	<code class="inline-code">object_wrapper</code> setting is
	<code class="inline-code">ObjectWrapper.DEFAULT_WRAPPER</code>. If you want to
	change it to, say, <code class="inline-code">ObjectWrapper.BEANS_WRAPPER</code>, you
	can configure the FreeMarker engine (before starting to use it from
	other threads) like this:</p>

	<div class="code-wrapper"><pre class="code-block code-unspecified">cfg.setObjectWrapper(ObjectWrapper.BEANS_WRAPPER);</pre></div><p>Note that you can set any object here that implements interface
	<code class="inline-code">ObjectWrapper</code>, so you can set your custom
	implementation as well.</p><p>For <code class="inline-code">TemplateModel</code> implementations that wrap
	basic Java container types, as <code class="inline-code">java.util.Map</code>-s and
	<code class="inline-code">java.util.List</code>-s, the convention is that they use
	the same object wrapper to wrap their subvariables as their parent
	container does. Technically correctly said, they are instantiated by
	their parent container (so it has full control over the creation of
	them), and the parent container create them so they will use the same
	object wrapper as the parent itself. Thus, if
	<code class="inline-code">BEANS_WRAPPER</code> is used for the wrapping of the root
	hash, it will be used for the wrapping of the subvariables (and the
	subvariables of the subvariables, etc.) as well. This is exactly the
	same phenomenon as you have seen with
	<code class="inline-code">theMap.anotherString</code> earlier.</p><div class="bottom-pagers-wrapper"><div class="pagers bottom"><a class="paging-arrow previous" href="pgui_datamodel_node.html"><span>Previous</span></a><a class="paging-arrow next" href="pgui_config.html"><span>Next</span></a></div></div></div></div> </div>
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