Welcome!

Weblogic Authors: Yeshim Deniz, Elizabeth White, Michael Meiner, Michael Bushong, Avi Rosenthal

Related Topics: Weblogic

Weblogic: Article

Building Web Applications in WebLogic

from Chapter 1

Web applications are an important part of the Java 2 Enterprise Edition (J2EE) platform because the Web components are responsible for key client-facing presentation and business logic. A poorly designed Web application will ruin the best business-tier com-ponents and services. In this chapter, we will review key Web application concepts and technologies and their use in WebLogic Server, and we will provide a number of recommendations and best practices related to Web application design and construction in WebLogic Server.

 This chapter also provides the foundation for the discussion of recommended Web application architectures in Chapter 2 and the construction and deployment of a com-plex, realistic Web application in Chapters 3, 4, and 5.

Java Servlets and JSP Key Concepts
In this section we will review some key concepts related to Java Servlets and JavaServer Pages. If you are unfamiliar with these technologies, or if you need addi-tional background material, you should read one of the many fine books available on the subject. Suggestions include Java Servlet Programming Bible by Suresh Rajagopalan et. al. (John Wiley & Sons, 2002), Java Servlet Programming by Jason Hunter (O'Reilly & Associates, 2001), and Core Servlets and JavaServer Pages by Marty Hall (Prentice Hall PTR, 2000).

Characteristics of Servlets
Java servlets are fundamental J2EE platform components that provide a request/response interface for both Web requests and other requests such as XML messages or file transfer functions. In this section, we will review the characteristics of Java servlets as background for a comparison of servlets with JavaServer Pages (JSP) technology and the presentation of best practices later in the chapter.

Servlets Use the Request/Response Model
Java servlets are a request/response mechanism: a programming construct designed to respond to a particular request with a dynamic response generated by the servlet's specific Java implementation. Servlets may be used for many types of request/response scenarios, but they are most often employed in the creation of HyperText Transfer Pro-tocol (HTTP) responses in a Web application. In this role, servlets replace other HTTP request/response mechanisms such as Common Gateway Interface (CGI) scripts.

The simple request/response model becomes a little more complex once you add chaining and filtering capabilities to the servlet specification. Servlets may now partic-ipate in the overall request/response scenario in additional ways, either by preprocessing the request and passing it on to another servlet to create the response or by postprocessing the response before returning it to the client. Later in this chapter, we'll discuss servlet filtering as a mechanism for adding auditing, logging, and debugging logic to your Web application.

Servlets Are Pure Java Classes
Simply stated, a Java servlet is a pure Java class that implements the javax.servlet .Servlet interface. The application server creates an instance of the servlet class and uses it to handle incoming requests. The Servlet interface defines the set of methods that should be implemented to allow the application server to manage the servlet life cycle (discussed later in this chapter) and pass requests to the servlet instance for processing. Servlets intended for use as HTTP request/response mechanisms normally extend the javax.servlet.http.HttpServlet class, although they may implement and use the Servlet interface methods if desired. The HttpServlet class implements the Servlet interface and implements the init(), destroy(), and service() methods in a default manner. For example, the service() method in HttpServlet interrogates the incoming HttpServletRequest object and for-wards the request to a series of individual methods defined in the HttpServlet class based on the type of request. These methods include the following:
-doGet() for handling GET, conditional GET, and HEAD requests - doPost() for POST requests
-doPut() for PUT requests
-doDelete() for DELETE requests
-doOptions() for OPTIONS requests - doTrace() for TRACE requests

The doGet(), doPost(), doPut(), and doDelete() methods in HttpServlet return a BAD_REQUEST (400) error as their default response. Servlets that extend HttpServlet typically override and implement one or more of these methods to gen-erate the desired response. The doOptions() and doTrace() methods are typically not overridden in the servlet. Their implementations in the HttpServlet class are designed to generate the proper response, and they are usually sufficient.

A minimal HTTP servlet capable of responding to a GET request requires nothing more than extending the HttpServlet class and implementing the doGet() method.

WebLogic Server provides a number of useful sample servlets showing the basic approach for creating HTTP servlets. These sample servlets are located in the samples/server/examples/src/examples/servlets subdirectory beneath the WebLogic Server home directory, a directory we refer to as $WL_HOME throughout the rest of the book. We will examine some additional example servlets in detail during the course of this chapter. These example servlets are available on the companion Web site for this book at www.wiley.com/compbooks/masteringweblogic.

Creating the HTML output within the servlet's service() or doXXX() method is very tedious. This deficiency was addressed in the J2EE specification by introducing a scripting technology, JavaServer Pages (JSP), discussed later in this chapter.

Servlets Have a Life Cycle
A servlet is an instance of the servlet class and has a life cycle similar to that of any other Java object. When the servlet is first required to process a request, the application server loads the servlet class, creates an instance of the class, initializes the instance, calls the servlet's init() method, and calls the service() method to process the request. In normal servlet operation, this same instance of the servlet class will be used for all subsequent requests.

Servlets may be preloaded during WebLogic Server startup by including the <load-on-startup> element in the web.xml file for the Web application. You can also pro-vide initialization parameters in this file using <init-param> elements. WebLogic Server will preload and call init() on the servlet during startup, passing the specified initialization parameters to the init() method in the ServletConfig object.

An existing servlet instance is destroyed when the application server shuts down or intends to reload the servlet class and create a new instance. The server calls the destroy() method on the servlet prior to removing the servlet instance and unload-ing the class. This allows the servlet to clean up any resources it may have opened dur-ing initialization or operation.

Servlets Allow Multiple Parallel Requests
Servlets are normally configured to allow multiple requests to be processed simultane-ously by a single servlet instance. In other words, the servlet's methods must be thread-safe. You must take care to avoid using class- or instance-level variables unless access is made thread-safe through synchronization logic. Typically, all variables and objects required to process the request are created within the service() or doXXX() method itself, making them local to the specific thread and request being processed.

BEST PRACTICE: Servlets that allow multiple parallel requests must be thread-safe. Do not share class- or instance-level variables unless synchronization logic provides thread safety.

Servlets may be configured to disallow multiple parallel requests by defining the servlet class as implementing the SingleThreadModel interface:

...
public class TrivialSingleThreadServlet
extends HttpServlet implements SingleThreadModel
{
public void init(ServletConfig config) throws ServletException
{
super.init(config); System.out.println("Here!");
}
...

This simple change informs the application server that it may not process multiple requests through the same servlet instance simultaneously. The application server can honor this restriction in multiple ways: It may block and queue up requests for pro-cessing through a single instance, or it may create multiple servlet instances as needed to fulfill parallel requests. The servlet specification does not dictate how application servers should avoid parallel processing in the same instance.

WebLogic Server satisfies the single-threaded requirement by creating a small pool of servlet instances (the default pool size is five) that are used to process multiple requests. In older versions of WebLogic Server, multiple parallel requests in excess of the pool size would block waiting for the first available servlet instance. This behavior changed in WebLogic Server 7.0. The server now creates, initializes, and discards a new instance of the servlet for each request rather than blocking an execute thread under these conditions. Set the pool size properly to avoid this extra servlet creation and initialization overhead.

You can configure the size of the pool at the Web application level using the single-threaded-servlet-pool-size element in the weblogic.xml deployment descriptor. If you choose to employ single-threaded servlets in high-volume applications, consider increasing the pool size to a level comparable to the number of execute threads in the server to eliminate the potential overhead required to create extra servlet instances on the fly to process requests.

Although instance variables are safe to use in single-threaded servlets, class-level static variables are shared between these instances, so access to this type of static data must be thread-safe even when using the SingleThreadModel technique. Deploy-ing and executing this TrivialSingleThreadServlet example verifies this pool-ing behavior in WebLogic Server. The first servlet request causes WebLogic Server to create five instances of the servlet, as evidenced by five separate invocations of the init() method and the subsequent writing of five "Here!" messages in the log.

Mastering BEA WebLogic Server, Best Practices for Building and Deploying J2EE Applications.

ISBN: 0-471-28128-X.
Published by Wiley

Authors:
Greg Nyberg, Robert Patrick with Paul Bauerschmidt, Jeff McDaniel, and Raja Mukherjee

Book Review
Mastering BEA WebLogic Server, Best Practices for Building and Deploying J2EE Applications is a new book for developers and architects. It covers many common areas experienced in the development and rollout of applications through J2EE and the use of BEA WebLogic Server. While the main audience is towards application developers and architects that have had some exposure to J2EE concepts and experience in development, beginners will find resource references and design patterns that will save a lot of extra work down the road.

The book covers Web applications, EJBs, and several other areas. There are three chapters on EJBs. Great care and time is spent discussing them in the BEA WebLogic Server context, including strategies in use, features, how to build, and typical packing and deployment of them. The remaining chapters cover JMS, security; administration/deployment; optimizing WebLogic Server performance, development, and production environment best practices; and developing/deployment of Web service applications. The first five chapters are on Web applications. Those covered focused on key concepts, best practices, architecture, package and deployment, and a sample walk-through.

Each section in a chapter normally contained best practice tips that are highlighted. Sample code was throughout the book, but there wasn't such an amount that you were reading code for the majority of a topic. Downloads are available to look through that exemplify the concepts the section is trying to portray. I like the fact that the authors bring out sections of BEA WebLogic Server that really aid in development or optimize performance, like the discussion of wl:cache.

In all, I found this book easy to read. I wished that there was more content on the security and deployment sections, but the information that was there established a strong basis for any team working with BEA WebLogic Server. I highly recommend this as a resource for any architect working with WebLogic Server. It will be a definite piece in my library.

by Eric Ballou ([email protected]

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, will discuss how from store operations...
SYS-CON Events announced today that IBM has been named “Diamond Sponsor” of SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California.
SYS-CON Events announced today that Ryobi Systems will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ryobi Systems Co., Ltd., as an information service company, specialized in business support for local governments and medical industry. We are challenging to achive the precision farming with AI. For more information, visit http:...
High-velocity engineering teams are applying not only continuous delivery processes, but also lessons in experimentation from established leaders like Amazon, Netflix, and Facebook. These companies have made experimentation a foundation for their release processes, allowing them to try out major feature releases and redesigns within smaller groups before making them broadly available. In his session at 21st Cloud Expo, Brian Lucas, Senior Staff Engineer at Optimizely, will discuss how by using...
In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lead...
SYS-CON Events announced today that Daiya Industry will exhibit at the Japanese Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ruby Development Inc. builds new services in short period of time and provides a continuous support of those services based on Ruby on Rails. For more information, please visit https://github.com/RubyDevInc.
SYS-CON Events announced today that CAST Software will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CAST was founded more than 25 years ago to make the invisible visible. Built around the idea that even the best analytics on the market still leave blind spots for technical teams looking to deliver better software and prevent outages, CAST provides the software intelligence that matter ...
As businesses evolve, they need technology that is simple to help them succeed today and flexible enough to help them build for tomorrow. Chrome is fit for the workplace of the future — providing a secure, consistent user experience across a range of devices that can be used anywhere. In her session at 21st Cloud Expo, Vidya Nagarajan, a Senior Product Manager at Google, will take a look at various options as to how ChromeOS can be leveraged to interact with people on the devices, and formats th...
SYS-CON Events announced today that Yuasa System will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Yuasa System is introducing a multi-purpose endurance testing system for flexible displays, OLED devices, flexible substrates, flat cables, and films in smartphones, wearables, automobiles, and healthcare.
SYS-CON Events announced today that Dasher Technologies will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Dasher Technologies, Inc. ® is a premier IT solution provider that delivers expert technical resources along with trusted account executives to architect and deliver complete IT solutions and services to help our clients execute their goals, plans and objectives. Since 1999, we'v...
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities – ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups. As a result, many firms employ new business models that place enormous impor...
SYS-CON Events announced today that Massive Networks, that helps your business operate seamlessly with fast, reliable, and secure internet and network solutions, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. As a premier telecommunications provider, Massive Networks is headquartered out of Louisville, Colorado. With years of experience under their belt, their team of...
SYS-CON Events announced today that Taica will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Taica manufacturers Alpha-GEL brand silicone components and materials, which maintain outstanding performance over a wide temperature range -40C to +200C. For more information, visit http://www.taica.co.jp/english/.
SYS-CON Events announced today that TidalScale, a leading provider of systems and services, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale has been involved in shaping the computing landscape. They've designed, developed and deployed some of the most important and successful systems and services in the history of the computing industry - internet, Ethernet, operating s...
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
SYS-CON Events announced today that TidalScale will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale is the leading provider of Software-Defined Servers that bring flexibility to modern data centers by right-sizing servers on the fly to fit any data set or workload. TidalScale’s award-winning inverse hypervisor technology combines multiple commodity servers (including their ass...
Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant tha...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
Infoblox delivers Actionable Network Intelligence to enterprise, government, and service provider customers around the world. They are the industry leader in DNS, DHCP, and IP address management, the category known as DDI. We empower thousands of organizations to control and secure their networks from the core-enabling them to increase efficiency and visibility, improve customer service, and meet compliance requirements.
As popularity of the smart home is growing and continues to go mainstream, technological factors play a greater role. The IoT protocol houses the interoperability battery consumption, security, and configuration of a smart home device, and it can be difficult for companies to choose the right kind for their product. For both DIY and professionally installed smart homes, developers need to consider each of these elements for their product to be successful in the market and current smart homes.