| <html><head> |
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| <title>2.9. Stateful Pages</title><link rel="stylesheet" href="css/stylesheet.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.75.0"><link rel="home" href="index.html" title="Apache Click"><link rel="up" href="ch02.html" title="Chapter 2. Pages"><link rel="prev" href="ch02s08.html" title="2.8. Direct Rendering"><link rel="next" href="ch02s10.html" title="2.10. Error Handling"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">2.9. Stateful Pages</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s08.html">Prev</a> </td><th width="60%" align="center">Chapter 2. Pages</th><td width="20%" align="right"> <a accesskey="n" href="ch02s10.html">Next</a></td></tr></table><hr></div><div class="sect1" title="2.9. Stateful Pages"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="stateful-pages"></a>2.9. Stateful Pages</h2></div></div></div><p><span class="symbol">PLEASE NOTE:</span> stateful pages have been deprecated in |
| Click 2.3.0 and will be removed in a future release. Do not use stateful pages |
| in your applications. Instead use stateful controls or HttpSession to store |
| state between requests. |
| </p><p>Click supports stateful pages where the state of the page is saved |
| between the users requests. Stateful pages are useful in a number of |
| scenarios including: |
| </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Search page and edit page interactions. In this scenario you |
| navigage from a stateful search page which may have filter criteria |
| applied to an object edit page. Once object update has been completed |
| on the edit page, the user is redirected to the search page and the |
| stateful filter criteria still applies. |
| </p></li><li class="listitem"><p>Complex pages with multiple forms and or tables which need to |
| maintain their state between interactions. |
| </p></li></ul></div><p>To make a page stateful you simply need to set the page |
| <a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="../../click-api/org/apache/click/Page.html#stateful" target="_blank">stateful</a> |
| property to true, have the page implement the <code class="classname">Serializable</code> |
| interface and set the <code class="literal">serialVersionUID</code> indicator. |
| For example: |
| </p><pre class="programlisting"><span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">package</span> com.mycorp.page; |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">import</span> java.io.Serializable; |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">import</span> org.apache.click.Page; |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">class</span> SearchPage <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">extends</span> Page <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">implements</span> Serializable { |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">private</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">static</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">final</span> <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">long</span> serialVersionUID = <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="lit">1L</span>; |
| |
| <span xmlns:fo="http://www.w3.org/1999/XSL/Format" class="kwd">public</span> SearchPage() { |
| setStateful(true); |
| .. |
| } |
| }</pre><p>Stateful page instances are stored in the user's |
| <a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="http://java.sun.com/products/servlet/2.3/javadoc/javax/servlet/http/HttpSession.html" target="_blank">HttpSession</a> |
| using the pages class name as the key. In the example above the page would |
| be stored in the users session using the class name: |
| <code class="classname">com.mycorp.page.SearchPage</code> |
| </p><div class="sect2" title="2.9.1. Page Creation"><div class="titlepage"><div><div><h3 class="title"><a name="page-creation"></a>2.9.1. Page Creation</h3></div></div></div><p>With stateful pages they are only created once, after which they |
| are retrieved from the session. However page event handlers are invoked |
| for each request, including the <code class="methodname">onInit()</code> method. |
| </p><p>When you are creating stateful pages you typically place all your |
| control creation code in the Pages constructor so it is invoked only once. |
| It is important not to place control creation code in the |
| <code class="methodname">onInit()</code> method which will be invoked with each |
| request. |
| </p><p>If you have dynamic control creation code you would typically place |
| this in the <code class="methodname">onInit()</code> method, but you will need to |
| take care that controls and or models are not already present in the page. |
| </p></div><div class="sect2" title="2.9.2. Page Execution"><div class="titlepage"><div><div><h3 class="title"><a name="page-execution"></a>2.9.2. Page Execution</h3></div></div></div><p>The default Click page execution model is thread safe as a new |
| Page instance is created for each request and thread. With stateful |
| pages a user will have a single page instance which is reused in multiple |
| requests and threads. To ensure page execution is thread safe, users page |
| instances are synchronized so only one request thread can execute a page |
| instance at any one time. |
| </p></div><div class="sect2" title="2.9.3. Page Destruction"><div class="titlepage"><div><div><h3 class="title"><a name="page-destruction"></a>2.9.3. Page Destruction</h3></div></div></div><p>After normal page instances have been executed, they are |
| de-referenced and garbage collected by the JVM. However with stateful |
| pages they are stored in the users <code class="classname">HttpSession</code> so |
| care needs to be take not to store too many objects in stateful page |
| instances which may cause memory and performance issues. |
| </p><p>When pages have completed their execution, all the Page's controls |
| <code class="methodname">onDestroy()</code> methods are invoked, and then the |
| Page's <code class="methodname">onDestroy()</code> method is invoked. This is |
| your opportunity to de-reference any large sets or graphs. For example the |
| Table control by default de-references its rowList in its |
| <a xmlns:fo="http://www.w3.org/1999/XSL/Format" class="external" href="../../click-api/org/apache/click/control/Table.html#onDestroy()" target="_blank">onDestory()</a> |
| method. |
| </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s08.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch02s10.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2.8. Direct Rendering </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 2.10. Error Handling</td></tr></table></div></body></html> |
