docs/1.2/web-applications.html

Title: Web Applications

	

<H3><A name="WebApplications-PuttingCayenneFilesinWebApplicationCLASSPATH"></A>Putting Cayenne Files in Web Application CLASSPATH</H3>

<P>When deploying an application in a web container it is possible to follow the procedure for the standalone applications, i.e. put all XML files in the application CLASSPATH (e.g. in &quot;mywebapp/WEB-INF/classes/&quot;, but DON'T put it in container shared locations!). Session DataContext can be obtained via ServletUtil:</P>

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<PRE class="code-java">HttpSession session = ...;
DataContext context = ServletUtil.getSessionContext(session);</PRE>
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<P>However you may consider a deployment procedure described below, as it provides more flexibility and a number of additional useful features.</P>

<H3><A name="WebApplications-CayenneServletFilter"></A>Cayenne Servlet Filter</H3>

<P>Adding the following filter to the <TT>web.xml</TT> would automate Cayenne setup in the web application:</P>

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<PRE>&lt;filter&gt;
    &lt;filter-name&gt;CayenneFilter&lt;/filter-name&gt;
    &lt;filter-class&gt;org.objectstyle.cayenne.conf.WebApplicationContextFilter&lt;/filter-class&gt;
&lt;/filter&gt;
&lt;filter-mapping&gt;
    &lt;filter-name&gt;CayenneFilter&lt;/filter-name&gt;
    &lt;url-pattern&gt;/*&lt;/url-pattern&gt;
&lt;/filter-mapping&gt;
</PRE>
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<P>The filter will ensure that for each matching request a DataContext is bound to the request thread. So you can retrieve it anywhere in the application, even if you don't have a reference to the web environment:</P>

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<PRE class="code-java">DataContext context = DataContext.getThreadDataContext();</PRE>
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<P>Filter can match a specific URL as shown above, or a specific servlet:</P>

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<PRE>&lt;servlet&gt;
   &lt;servlet-name&gt;MyServlet&lt;/servlet-name&gt;
   &lt;servlet-class&gt;org.example.MyServlet&lt;/servlet-class&gt;
   &lt;load-on-startup&gt;0&lt;/load-on-startup&gt;
&lt;/servlet&gt;
		
&lt;filter&gt;
    &lt;filter-name&gt;CayenneFilter&lt;/filter-name&gt;
    &lt;filter-class&gt;org.objectstyle.cayenne.conf.WebApplicationContextFilter&lt;/filter-class&gt;
&lt;/filter&gt;
&lt;filter-mapping&gt;
    &lt;filter-name&gt;CayenneFilter&lt;/filter-name&gt;
    &lt;servlet-name&gt;MyServlet&lt;/servlet-name&gt;
&lt;/filter-mapping&gt;</PRE>
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<P>Additionally the filter supports putting files in <TT>myapp/WEB-INF/</TT> directory instead of the CLASSPATH, so a .war file may look like this:</P>

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<PRE>index.jsp
WEB-INF/cayenne.xml
WEB-INF/xyz.map.xml
WEB-INF/lib/...</PRE>
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<P>Actually, Cayenne files can be stored in any subdirectory of <TT>myapp/WEB-INF/</TT>. To specify a subdirectory, you'll need to add <TT>&lt;context-param&gt;</TT> named <TT>cayenne.configuration.path</TT> to your application descriptor:</P>

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<PRE>&lt;context-param&gt;
    &lt;param-name&gt;cayenne.configuration.path&lt;/param-name&gt;
    &lt;param-value&gt;/WEB-INF/config/cayenne-files&lt;/param-value&gt;
&lt;/context-param&gt;</PRE>
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