7 Configuring Resources in a Web Application

Configuring Resources in a Web Application

The resources that you use in a Web application are generally deployed externally to the Web application. JDBC DataSources can optionally be deployed within the scope of the Web application as part of an EAR file.

To use external resources in the Web application, you resolve the JNDI resource name that the application uses with the global JNDI resource name using the web.xml and weblogic.xml deployment descriptors. (The web.xml file is located in the WEB-INF directory of your Web application.) See Configuring Resources for more information.

You can also deploy JDBC DataSources as part of the Web application EAR file by configuring those resources in the weblogic-application.xml deployment descriptor. Resources deployed as part of the EAR file with scope defined as application are referred to as application-scoped resources. These resources remain private to the application, and application components can access the resource names by adding <resource-ref> as explained in Configuring Resources.

Configuring Resources

When accessing resources such as a DataSource from a Web application through Java Naming and Directory Interface (JNDI), you can map the JNDI name you look up in your code to the actual JNDI name as bound in the global JNDI tree. This mapping is made using both the web.xml and weblogic.xml deployment descriptors and allows you to change these resources without changing your application code. You provide a name that is used in your Java code, the name of the resource as bound in the JNDI tree, and the Java type of the resource, and you indicate whether security for the resource is handled programmatically by the servlet or from the credentials associated with the HTTP request. You can also access JMS module resources, such as queues, topics, and connection factories. For more information see, "Configuring JMS Application Modules for Deployment" in Oracle Fusion Middleware Configuring and Managing JMS for Oracle WebLogic Server.

To configure resources:

1. Enter the resource name in the deployment descriptor as you use it in your code, the Java type, and the security authorization type.

2. Map the resource name to the JNDI name.

   The following example illustrates how to use an external DataSource. It assumes that you have defined a data source called accountDataSource. For more information, see "JDBC Data Sources " in Oracle Fusion Middleware Oracle WebLogic Server Administration Console Help.

javax.sql.DataSource ds = (javax.sql.DataSource) ctx.lookup
                           ("myDataSource");
web.xml entries:
<resource-ref>
. . .
   <res-ref-name>myDataSource</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
   <res-auth>CONTAINER</res-auth>
. . .
</resource-ref>
weblogic.xml entries:
<resource-description>
   <res-ref-name>myDataSource</res-ref-name>
   <jndi-name>accountDataSource</jndi-name>
</resource-description>

Referencing External EJBs

Web applications can access EJBs that are deployed as part of a different application (a different EAR file) by using an external reference. The EJB being referenced exports a name to the global JNDI tree in its weblogic-ejb-jar.xml deployment descriptor. An EJB reference in the Web application module can be linked to this global JNDI name by adding an ejb-reference-description element to its weblogic.xml deployment descriptor.

This procedure provides a level of indirection between the Web application and an EJB and is useful if you are using third-party EJBs or Web applications and cannot modify the code to directly call an EJB. In most situations, you can call the EJB directly without using this indirection. For more information, see Oracle Fusion Middleware Programming Enterprise JavaBeans for Oracle WebLogic Server.

To reference an external EJB for use in a Web application:

1. Enter the EJB reference name you use to look up the EJB in your code, the Java class name and the class name of the home and remote interfaces of the EJB in the ejb-ref element of the J2EE standard deployment descriptor, web.xml. (The web.xml file is located in the WEB-INF directory of your Web application.)

2. Map the reference name in the ejb-reference-description element of the WebLogic-specific deployment descriptor, weblogic.xml, to the JNDI name defined in the weblogic-ejb-jar.xml file.

   If the Web application is part of an Enterprise Application Archive (EAR file), you can reference an EJB by the name used in the EAR with the ejb-link element of the J2EE standard deployment descriptor, web.xml.

More about the ejb-ref* Elements

The ejb-ref element in the web.xml deployment descriptor declares that either a servlet or JSP is going to be using a particular EJB. The ejb-reference-description element in the weblogic.xml deployment descriptor binds that reference to an EJB, which is advertised in the global JNDI tree.

The ejb-reference-descriptor element indicates which ejb-ref element it is resolving with the ejb-ref-name element. That is, the ejb-reference-descriptor and ejb-ref elements with the same ejb-ref-name element go together.

With the addition of the ejb-link syntax, the ejb-reference-descriptor element is no longer required if the EJB being used is in the same application as the servlet or JSP that is using the EJB.

The ejb-ref-name element serves two purposes in the web.xml deployment descriptor:

• It is the name that the user code (servlet or JSP) uses to look up the EJB. Therefore, if your ejb-ref-name element is ejb1, you would perform a JNDI name lookup for ejb1 relative to java:comp/env. The ejb-ref-name element is bound into the component environment (java:comp/env) of the Web application containing the servlet or JSP.

  Assuming the ejb-ref-name element is ejb1, the code in your servlet or JSP should look like:

  Context ctx = new InitialContext(); 
  ctx = (Context)ctx.lookup("java:comp/env"); 
  Object o = ctx.lookup("ejb1"); 
  Ejb1Home home = (Ejb1Home) PortableRemoteObject.narrow(o, Ejb1Home.class);
  

• It links the ejb-ref and ejb-reference-descriptor elements together.

Referencing Application-Scoped EJBs

Within an application, WebLogic Server binds any EJBs referenced by other application components to the environments associated with those referencing components. These resources are accessed at runtime through a JNDI name lookup relative to java:comp/env.

The following is an example of an application deployment descriptor (application.xml) for an application containing an EJB and a Web application, also called an Enterprise Application. (For the sake of brevity, the XML header is not included in this example.)

<application>
     <display-name>MyApp</display-name>
     <module>
        <web>
           <web-uri>myapp.war</web-uri>
           <context-root>myapp</context-root>
        </web>
     </module>
     <module>
        <ejb>ejb1.jar</ejb>
     </module>
  </application>

filename#ejbname 

<ejb-link>../ejb1.jar#myejb</ejb-link>

<ejb-link>myejb</ejb-link>

<web-app>
   ...
   <ejb-ref>
      <ejb-ref-name>ejb1</ejb-ref-name>
      <ejb-ref-type>Session</ejb-ref-type>
      <home>mypackage.ejb1.MyHome</home>
      <remote>mypackage.ejb1.MyRemote</remote>
      <ejb-link>../ejb1.jar#myejb</ejb-link>
   </ejb-ref>
   ...
 </web-app>

<ejb-link>../ejb1.jar#ejb1</ejb-link>,

<ejb-jar>
   ...
   <enterprise-beans>
      <session>
         <ejb-name>myejb</ejb-name>
         <home>mypackage.ejb1.MyHome</home>
         <remote>mypackage.ejb1.MyRemote</remote>
         <ejb-class>mypackage.ejb1.MyBean</ejb-class>
         <session-type>Stateless</session-type>
         <transaction-type>Container</transaction-type>
      </session>
   </enterprise-beans>
   ...
 </ejb-jar>

MyHome home = (MyHome)ctx.lookup("java:/comp/env/ejb1");

Serving Resources from the CLASSPATH with the ClasspathServlet

If you need to serve classes or other resources from the system CLASSPATH, or from the WEB-INF/classes directory of a Web application, you can use a special servlet called the ClasspathServlet. The ClasspathServlet is useful for applications that use applets or RMI clients and require access to server-side classes. The ClasspathServlet is implicitly registered and available from any application.

The ClasspathServlet is always enabled by default. To disable it, set the ServerMBean parameter ClassPathServletDisabled to true (default = false).

The ClasspathServlet returns the classes or resources from the system CLASSPATH in the following order:

1. WEB-INF/classes

2. jar files under WEB-INF/lib/*

3. system CLASSPATH

To serve a resource from the WEB-INF/classes directory of a Web application, call the resource with a URL such as:

http://server:port/myWebApp/classes/my/resource/myClass.class

In this case, the resource is located in the following directory, relative to the root of the Web application:

WEB-INF/classes/my/resource/myClass.class

Using CGI with WebLogic Server

WebLogic Server supports all CGI scripts through an internal WebLogic servlet called the CGIServlet. To use CGI, register the CGIServlet in the Web application deployment descriptor. See Configuring How a Client Accesses a Web Application.

<servlet>
 <servlet-name>CGIServlet</servlet-name>
 <servlet-class>weblogic.servlet.CGIServlet</servlet-class>
 <init-param>
  <param-name>cgiDir</param-name>
  <param-value>
   /bea/wlserver6.0/config/mydomain/applications/myWebApp/cgi-bin
  </param-value>
 </init-param>
  <init-param>
   <param-name>*.pl</param-name>
   <param-value>/bin/perl.exe</param-value>
  </init-param>
</servlet>
...
<servlet-mapping>
   <servlet-name>CGIServlet</servlet-name>
   <url-pattern>/cgi-bin/*</url-pattern>
</servlet-mapping>

http://host:port/myWebApp/cgi-bin/myscript.pl