OC4J Listeners Oracle Application Server Tips by Burleson Consulting

To allow access to an OC4J instance, the container maintains a number of listeners that listen on a port for a request and then pass that request to the container.  On the OC4J Server Properties page (Figure 7), a range of ports was defined for three methods of access. 

Most web applications connect to the Oracle HTTP Server (OHS) and communicate through the Apache Java API (AJP).  Another method uses a Java program to directly call a method belonging to an EJB in the container.  This is referred to as a Remote Method Invokation (RMI).  An RMI connection bypasses the OHS and communicates directly with the OC4J container.  Finally, the container can be passed Java Messages using JMS. 

OC4J containers normally maintain listeners for each of these connection strategies.  When the Oracle9iAS instance is installed, it is configured to listen for HTTP requests on port 7777.  If that port is in use, the configuration program will increment the port number by one until it finds an unused port.  The configuration utility configures the HTTP port in the file: http-web-site.xml.  OHS will listen for HTTP requests on that port.      If you remember the Server Properties Page (Figure 7), there was a range of ports defined for AJP.  When OHS starts up, it negotiates with the OC4J container for an available port within the defined range. Because OHS cannot communicate with the container using AJP and receive an HTTP request on the same port, you must insure that the port range available for AJP does not contain the HTTP request port.  The AJP port is defined in the default-web-site.xml file. If it is defined as 0, then OHS and the container negotiate the port within the defined port range.  If is defined as a port other than 0, then OHS and the container will use the defined port. 

Remote Method Invocation also requires the use of a listener.  The RMI listener is defined in the file rmi.xml, located in the Server Root directory.  This port is defined during OC4J container creation and can only be modified in the Advanced Properties section of the container Home Page. 

The Java Message Service API also uses a listener that is defined initially at container creation.  This port is located in the jms.xml file.

<jms-server port="9127">

It is important to remember that one port can only support one listener.  You must insure that the ports defined at the creation of the instance or are not included in the available ports for negotiated listener ports.     

The OC4J container is the heart of the application server, supporting web components and EJBs with communications, security, and reliability.  Future chapters will build on the capabilities discussed in this chapter, as we tie all the parts together that make up the Application Server.  Now that we can configure our container and deploy an application into it, we need to connect that application to a persistent storage or database.

 
This is an excerpt from "Oracle 10g Application Server Administration Handbook" by Don Burleson and John Garmany.