Oracle Web Listener

The Oracle Web Listener still exists as an HTTP engine, but it is deprecated and will be desupported in a future Oracle Application Express release. Oracle recommends using Oracle REST Data Services instead. The Oracle Web Listener is a lightweight HTTP server that can be used to host Oracle Application Express applications. It is based on the Apache HTTP Server and includes a number of Oracle-specific features, such as the mod_plsql module for serving PL/SQL applications.
Oracle REST Data Services is a more modern and feature-rich HTTP engine that is designed to support Oracle Application Express and other Oracle Fusion Middleware applications. It offers a number of advantages over the Oracle Web Listener, including:

1. Improved performance and scalability
2. Support for file system caching
3. Improved file upload capability
4. Certification with Oracle WebLogic Server, Oracle Glassfish Server, and Apache Tomcat

If you are using the Oracle Web Listener, it is recommended that you migrate to Oracle REST Data Services as soon as possible.

• Second Component of Web architecture is the Web Listener The second component of Web architecture is the Web Listener. The Web Listener is an HTTP engine, similar to an Oracle background process, located on the Oracle host that manages incoming requests for services. Each host may have many listener processes running, depending on the processing needs of the Oracle WebServer. The following series of images below describes the role of the Web Listener.

The evolution of Oracle Web Listener and Oracle REST Data Services (ORDS) from Oracle 11g to Oracle 19c has seen significant improvements and changes in functionality, architecture, and performance.
Oracle Web Listener:

1. Oracle 11g:
   • The Web Listener in Oracle 11g was primarily associated with Oracle HTTP Server (OHS), which was based on Apache HTTP Server. It served as the primary web listener for Oracle Fusion Middleware components and allowed for the deployment of various web applications, including those that accessed Oracle databases.
   • Oracle 11g also supported Oracle XML DB HTTP Server as a light-weight HTTP server built into the database, providing basic HTTP services like serving static content and supporting web-based access to XML DB resources.
2. Oracle 19c:
   • By Oracle 19c, the focus has shifted more towards Oracle REST Data Services (ORDS) as a central component for web-based interactions with the Oracle Database. While Oracle HTTP Server still exists, it's more aligned with Oracle Fusion Middleware, and the reliance on it for database-driven web services has decreased.
   • Oracle XML DB HTTP Server has been further integrated and optimized within the database, providing more streamlined and secure HTTP-based access.

Oracle REST Data Services (ORDS):

1. Oracle 11g:
   • ORDS was not as prominent during the Oracle 11g era. The primary focus for web services was on tools like Oracle Application Express (APEX) and manual creation of web services using PL/SQL or Java stored procedures.
   • ORDS (formerly known as APEX Listener) was used primarily to support Oracle APEX applications, providing a RESTful interface to the database, but it was still in its early stages and not as feature-rich as it would later become.
2. Oracle 19c:
   • ORDS has become a central component for enabling RESTful services on top of the Oracle Database. It allows developers to create, deploy, and manage RESTful web services that interact directly with the database, making it easier to expose database functionality over HTTP.
   • ORDS supports modern web service standards, integrates deeply with Oracle APEX, and allows for declarative RESTful web service creation, which simplifies the process significantly compared to earlier versions.
   • It also includes features such as auto-REST enabling of tables and views, OAuth2 authentication support, and better integration with Oracle Cloud services.

Key Improvements:

• Performance and Scalability: Oracle 19c with ORDS has seen significant improvements in performance and scalability, supporting high-volume transactions and large-scale web applications more effectively than Oracle 11g.
• Security Enhancements: ORDS in Oracle 19c includes more robust security features, including better authentication and authorization mechanisms.
• Simplified Development: The development process for web services has been simplified in Oracle 19c, with tools and wizards available to help developers create RESTful services without needing to write extensive PL/SQL code.

In summary, from Oracle 11g to Oracle 19c, the web services landscape within Oracle has evolved from basic HTTP servers and manual web service creation to a more integrated, secure, and feature-rich environment with Oracle REST Data Services at its core.

You can choose any one of the three Web listeners

1. Oracle REST Data Services,
2. Oracle HTTP Server, and
3. Embedded PL/SQL gateway.

Oracle Application Express uses a simple architecture where pages are dynamically generated using metadata stored within the Oracle Database. There is no code generation or file based compilation. Once fully installed, a Uniform Resource Locator (URL) is defined for both developers and end users to access Oracle Application Express. Users require only a Web browser and the required URL and no additional client software is required.

The Web listener functions as a communications broker between the Web browser and the Oracle Application Express objects in the Oracle database by mapping browser requests into database stored procedure calls. You have a choice of three Web listeners.

1. Oracle REST Data Services (formerly Oracle Application Express Listener).
2. Oracle HTTP Server.
3. Embedded PL/SQL gateway.