Chapter-01: Introduction to Weblogic Server

Friends, before going into the details of the technology, lets first understand the basics of Weblogic Server.

What is Weblogic Server ?

• WebLogic Server is an application server: a platform for developing and deploying multitier distributed enterprise applications.


• WebLogic Server centralizes application services such as Web server functionality, business components, and access to backend enterprise systems.


• It uses technologies such as caching and connection pooling to improve resource use and application performance.


• WebLogic Server also provides enterprise-level security and powerful administration facilities.


• WebLogic Server operates in the middle tier of a multitier (or n-tier) architecture.


• A multitier architecture determines where the software components that make up a computing system are executed in relation to each other and to the hardware, network, and users. Choosing the best location for each software component lets you develop applications faster; eases deployment and administration; and provides greater control over performance, utilization, security, scalability, and reliability.


• WebLogic Server implements J2EE, the Java Enterprise standard.

[Courtesy for this section : Oracle docs]

Understanding the Software Component Tiers:

[Courtesy for this section: Oracle docs]

In today's world almost every enterprise application runs on a three-tier architecture which is also referred as n-tier architecture.

A typical three tier architecture looks like :



PICTURE: 3-tier architecture 

Now, Lets understand all these 3 -tiers and its functions:

• Client Tier:
  
  
  
  • It consists of the application or program at the user end for example a web browser.
  
  
  • WebLogic Server clients use standard interfaces to access WebLogic Server services.
  
  
  • WebLogic Server has complete Web server functionality, so a Web browser can request pages from WebLogic Server using the Web's standard HTTP/S protocol.
  
  
  • WebLogic Server servlets and JavaServer Pages (JSPs) produce the dynamic, personalized Web pages required for advanced e-commerce Web applications

1. Middle Tier:
   
   
   
   • The middle tier contains WebLogic Server and other servers that are addressed directly by clients, such as existing Web servers or proxy servers.
   
   
   • includes WebLogic Server and other Web servers, firewalls, and proxy servers that mediate traffic between clients and WebLogic Server
   
   
   • Applications based on a multitier architecture require reliability, scalability, and high performance in the middle tier. The application server you select for the middle tier is, therefore, critical to the success of your system.
   
   
   • The WebLogic Server cluster option allows you to distribute client requests and back-end services among multiple cooperating WebLogic Servers. Programs in the client tier access the cluster as if it were a single WebLogic Server. As the workload increases, you can add WebLogic Servers to the cluster to share the work. The cluster uses a selectable load-balancing algorithm to choose a WebLogic Server in the cluster that is capable of handling the request.
   
   
   • When a request fails, another WebLogic Server that provides the requested service can take over. Failover is transparent whenever possible, which minimizes the amount of code that must be written to recover from failures. For example, servlet session state can be replicated on a secondary WebLogic Server so that if the WebLogic Server that is handling a request fails, the client's session can resume uninterrupted on the secondary server. WebLogic EJB, JMS, JDBC, and RMI services are all implemented with clustering capabilities.


2. Backend Tier:
   
   
   
   • The backend tier contains enterprise resources, such as database systems, mainframe etc...
   
   
   • The backend tier contains services that are accessible to clients only through WebLogic Server.
   
   
   • Applications in the backend tier tend to be the most valuable and mission-critical enterprise resources. WebLogic Server protects them by restricting direct access by end users.
   
   
   • With technologies such as connection pools and caching, WebLogic Server uses back-end resources efficiently and improves application response.
   
   
   • A database management system is the most common backend service, required by nearly all WebLogic Server applications. WebLogic EJB and WebLogic JMS typically store persistent data in a database in the backend tier

NOTE-1:Client applications access WebLogic Server directly, or through another Web server or proxy server. WebLogic Server generally connects with backend services on behalf of clients. However, clients may directly access backend services using a multitier JDBC driver.

NOTE-2: For detailed description I would request you to follow the below link https://docs.oracle.com/cd/E13222_01/wls/docs81/intro/chap1.html