<s1 title="Servlet Applications"><summarylist/><s2 title='Introduction'><p>An application collects servlets, JSP pages, scripts and Java Beans into aself-contained web application.  Applications are just generalized virtualhosts, only based on the URL instead of the host name.</p><p>For example, abulletin board application groups pages for article reading, grouplisting, user registration, and new article posting into a singleapplication.</p><p>Applications can keep track of user sessions, giving the users theillusion of a single application out of disjoint pages.</p><ul><li>Resin organizes applications with an application <ahref='#dir'>directory</a>, WEB-INF<li><a href='#session'>Sessions</a> share state for a user's visit tothe site.</ul><p>Many, if not most sites, will only use the default application.</p></s2><s2 name='dir' title='Applications'><deftable title='application contents'><tr><th>File/Directory</th><th>Contents</th></tr><tr><td>.</td><td>JSP, HTML and GIF files</td></tr><tr><td>WEB-INF/classes</td><td>Java class files</td></tr><tr><td>WEB-INF/lib</td><td>Java jars</td></tr><tr><td>WEB-INF/tmp</td><td>Temporary servlet files</td></tr><tr><td>WEB-INF/work</td><td>Generated java for JSP and XSL</td></tr></deftable><ul class=none><li><ct:img src='folder.gif'/>&nbsp;example<ul class=none>  <li><ct:img src='file.gif'/>&nbsp;index.html  <li><ct:img src='file.gif'/>&nbsp;folder.gif  <li><ct:img src='file.gif'/>&nbsp;article.gif  <li><ct:img src='jsp.gif'/>&nbsp;post-article.xtp  <li><ct:img src='folder.gif'/>&nbsp;jsp-interest  <ul class=none>    <li><ct:img src='jsp.gif'/>&nbsp;index.jsp    <li><ct:img src='jsp.gif'/>&nbsp;article1.jsp    <li><ct:img src='jsp.gif'/>&nbsp;article2.jsp  </ul>  <li><ct:img src='folder.gif'/>&nbsp;WEB-INF  <ul class=none>    <li><ct:img src='folder.gif'/>&nbsp;lib    <ul class=none>      <li><ct:img src='bean.gif'/>&nbsp;bulletin-board.jar    </ul>    <li><ct:img src='folder.gif'/>&nbsp;classes    <ul class=none>      <li><ct:img src='bean.gif'/>&nbsp;Navigation.class      <li><ct:img src='bean.gif'/>&nbsp;HelloWorld.class    </ul>    <li><ct:img src='folder.gif'/>&nbsp;xsl    <ul class=none>      <li><ct:img src='style.gif'/>&nbsp;default.xsl      <li><ct:img src='style.gif'/>&nbsp;article.xsl    </ul>  </ul></ul></ul></s2><s2 name=beans title='JSP Beans'><p>Java Beans get first class treatment in JSP 1.0.  Beans can becreated for a page, across a session, or for the entire application.</p><p>The classes and lib directories can contain application beans used by <ahref='jsp-actions.xtp#usebean'>jsp:useBean</a>.  These are simply Javaclasses implementing the bitmechanic work of an application.</p><p>For example, a shopping cart application may have a set of Javaclasses that perform the security necessary for credit cardprocessing.  The application can put those classes in the beansdirectory and access them from the JSP page.</p><p>Beans can be created with different lifetimes.</p><ul><li>Application beans last the lifetime of an application.<li>Session beans last for a user's session.<li>Request beans last for a single request.<li>Page beans only last for a single page.</ul><p>Requests and pages often last the same lifetime, but may differ if onepage <a href='jsp-actions.xtp#forward'>forwards</a> or <ahref='jsp-actions.xtp#include'>includes</a> another page. </p><s3 title='Accessing Beans'><p>Each bean is defined with a <a href='jsp.xtp#usebean'>jsp:useBean</a>directive.</p><p>JSP assigns the created bean object to the JavaScript variablenamed by jsp:useBean.</p><p>In addition, the created beans are stored in JSP variables: pagebeans are stored in <code/request/>, session beans are stored in<code/session/>, and application beans are stored in<code/application/>.  Storing the beans in the JSP variables letsother beans and functions retrieve the beans.</p><example title='Beans in variables: test.jsp'>&lt;jsp:useBean id='test' class='java.util.Hashtable'&gt;&lt% test.put("a", 1); %&gt;&lt%= test.get("a"); %&gt;</example><example title='Page beans in request: test.jsp'>&lt;jsp:useBean id='test' class='java.util.Hashtable'&gt;&lt;%   var t = request.attributes.test  t.put("a", 1);%&gt;&lt%= test.get("a"); %&gt;</example><results>1</results></s3></s2><s2 name=session title='Sessions'><p>Session variables let applications keep track of the user as she movesthrough the site.  Any e-commerce site needs this capability to keeptrack of the user's purchases.</p><p>JSP sessions start when the page accesses the <ahref='jsp-variables.xtp#session'>session</a> variable.</p><p>Sessions end when the session times out, when the session isinvalidated, or when the application ends.</p></s2></s1>