In this section I will describe you the Controller part of the Struts Framework. I will show you how to configure the struts-config.xml file to map the request to some destination servlet or jsp file.
The class org.apache.struts.action.ActionServlet is the heart of the Struts Framework. It is the Controller part of the Struts Framework. ActionServlet is configured as Servlet in the web.xml file as shown in the following code snippets.
<!-- Standard Action Servlet Configuration (with debugging) -->
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
<init-param>
<param-name>config</param-name>
<param-value>/WEB-INF/struts-config.xml</param-value>
</init-param>
<init-param>
<param-name>debug</param-name>
<param-value>2</param-value>
</init-param>
<init-param>
<param-name>detail</param-name>
<param-value>2</param-value>
</init-param>
<load-on-startup>2</load-on-startup>
</servlet> |
This servlet is responsible for handing all the request for the Struts Framework, user can map the specific pattern of request to the ActionServlet. <servlet-mapping> tag in the web.xml file specifies the url pattern to be handled by the servlet. By default it is *.do, but it can be changed to anything. Following code form the web.xml file shows the mapping.
<!-- Standard Action Servlet Mapping -->
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping> |
The above mapping maps all the requests ending with .do to the ActionServlet. ActionServlet uses the configuration defined in struts-config.xml file to decide the destination of the request. Action Mapping Definitions (described below) is used to map any action. For this lesson we will create Welcome.jsp file and map the "Welcome.do" request to this page.
Welcome.jsp
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<%@ taglib uri="/tags/struts-bean" prefix="bean" %>
<%@ taglib uri="/tags/struts-html" prefix="html" %>
<html:html locale="true">
<head>
<title><bean:message key="welcome.title"/></title>
<html:base/>
</head>
<body bgcolor="white">
<h3><bean:message key="welcome.heading"/></h3>
<p><bean:message key="welcome.message"/></p>
</body>
</html:html>
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Forwarding the Welcome.do request to Welcome.jsp
The "Action Mapping Definitions" is the most important part in the struts-config.xml. This section takes a form defined in the "Form Bean Definitions" section and maps it to an action class.
Following code under the <action-mappings> tag is used to forward the request to the Welcome.jsp.
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<action path="/Welcome"
forward="/pages/Welcome.jsp"/>
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To call this Welcome.jsp file we will use the following code.
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<html:link page="/Welcome.do">First Request to the controller</html:link>
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Once the use clicks on on First Request to the controller link on the index page, request (for Welcome.do) is sent to the Controller and the controller forwards the request to Welcome.jsp. The content of Welcome.jsp is displayed to the user.