29
Fri, Nov
0 New Articles

Servlets: The New Application Architecture

Java
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

Like many of you, I have spent my professional programming career looking for ways IT can give my company an edge over the competition. I have seen firsthand the benefits of cross-platform object-oriented programming. Unfortunately, I have experienced problems with scalability, security, system complexity, and data integrity. I would like to find a system that is easy to use, has an integrated database, can be accessed from the Internet, and supports a powerful object-oriented language. As the ad says, “...that would change everything.” With Java servlets, JavaServer Pages (JSPs), IBM WebSphere, and the AS/400, perhaps there is finally a winning combination.

Web Application Servers

When Java first came on the scene, it seemed a perfect fit for the AS/400. At last, maybe there was a worthy successor to RPG. But would Java “play nice” on the AS/400? Could I leverage my company’s investment in several million lines of RPG code and a database developed over a period of years? Could I draw a line in the sand, stop developing in RPG, and switch over to Java without skipping a beat? My initial experiences with Java answered those questions with a firm no, but, after the completion of my most recent project, the answer is now maybe.

The New Application Architecture

At this time, you have several practical ways to run Java programs on an AS/400. You can run them as batch programs (OK). You can run them interactively from a command prompt using Run Java (RUNJVA) (slow). You can run them within the Qshell environment (slow). They can be called from RPG or CL programs (if you like pain). Or you can run them from a Web application server, such as WebSphere (now we’re talking). WebSphere provides a Web-enabled environment that lets you focus on the applications and not the supporting infrastructure. You don’t want to spend time thinking about managing a user’s connection to your system, nor do you want to manage database connections. In the green- screen world, you didn’t worry about this background stuff. When was the last time you, as a programmer, worried about how the user obtained a sign-on screen? You need to


concentrate on writing the application to solve business problems, and the operating environment should handle all the background stuff.

One of the last remaining sore points I had against Java was that the code for the user interface was often embedded within the business logic. In the GUI world, this can be incredibly time-consuming for the programmer. In the RPG world, you are used to creating a display file with SDA and then being free to focus on the business logic in the RPG code. The addition of JSPs brings this same freedom to the Java servlet world. JSPs handle the formatting of data for the user interface, and Java servlets handle the management of data. The combined use of JSP and servlets allows you to separate the business and presentation logic.

Figure 1 shows the basic configuration I recommend. A typical interactive session with a user is as follows:

1. A user starts up his favorite Web browser.

2. The browser’s URL references an AS/400-based Web site.

3. The AS/400’s HTTP server services the user’s request by sending an initial HTML Web page to the browser (the initial page is analogous to a 5250 menu).

4. The user clicks on a menu option of the Web page.

5. The browser sends the user’s request to the AS/400-based site powered by WebSphere (or some other Web application server that supports servlets).

6. The Web application server recognizes a request to run a servlet

(like a green-screen menu trying to run an RPG program). The Web application server starts up the servlet, creating a unique environment for this session, and passes to the servlet the user’s menu option request.

7. The Java servlet, as an application controller, responds to the user’s request by accessing the database (either with direct database calls, RPG/legacy program calls, or Enterprise JavaBeans). The servlet then crunches the retrieved data with its business logic, and, finally, the servlet assembles that crunched data into the information required to respond to the user.

8. The servlet puts all the acquired data into a JavaBean object (often called view beans or smart parameters) and forwards control to a JSP (kind of like an EXFMT in an RPG program).

9. The JSP formats the data contained in the passed view bean into a Web page.

10. WebSphere passes the dynamically constructed Web page back to the browser so the user can view the response.


Not too bad, huh? This process is similar to that of your RPG programs and 5250 display files. You only had to code four pieces: the initial HTML page, to contain a menu; the Java servlet, which contains the business logic; the JavaBean, which holds the display data; and the JSP, which generates the user interface. (See the sidebar, “HTML, Servlets, JSPs, and JavaBeans: A Code Example,” to see how information is processed in this new application architecture.) One thing I can’t convey in the simple diagram shown in Figure 1 is that, in real life, this setup, without adequate performance tuning, runs like a dog. The 1 to 2 second response time you are used to in RPG may turn into several minutes with an improperly tuned Java application. My article, “A Programmer’s Notebook: Making Servlets Run Faster,” on page 78 lists a number of tips that you can use to make your server-side applications as fast as your legacy RPG applications.

HTML, Servlets, JSPs, and JavaBeans: A Code Example

At first glance, the new application architecture that Alex Garrison used to transform his company’s IT applications sounds fairly complex. But, as Alex explains, “This process is similar to that of your RPG programs and 5250 display files.” I’m going to prove Alex’s statement with the retrieve customer information example shown in Figure A1 and Figure A2.

Figure A3 shows the HTML code for Figure A1; it simply prompts the user for a customer number. The most important line of the HTML code is this form tag:

The Action option of the form tag qualifies a Java servlet called GetCustomer as the server-side application that is to handle the user request. When the user clicks the Submit button, your Web application server will invoke the GetCustomer program shown in Figure A4. The init function (or method in object-oriented parlance) of the GetCustomer class sets up a connection to DB2/400, but it’s the doGet method that does the work of responding to the user’s HTML-based request. The doGet method retrieves the customer number with the getParameter method, uses that number to create a Customer JavaBean (by invoking its getCustomer method that uses SQL to retrieve the customer data), sets that JavaBean as an attribute/parameter of the user request, and passes control to a JavaServer Page (JSP).

The Customer JavaBean, shown in Figure A5, is an example of what I call a “smart parameter” because essentially it is simply a data structure with functions that is passed as a parameter to a JSP. The *ENTRY *PLIST of JSP, shown in Figure A6, that references the smart parameter is the jsp:useBean tag. The JSP retrieves values out of the JavaBean with the getName and getAddress methods. Note that Java code of the JSP is nested between pairs of <% and %>. Otherwise, the JSP contains standard HTML code.

—Don Denoncourt

Don Denoncourt is a senior technical editor for Midrange Computing. Don has six years of object-oriented design and programming experience and now considers himself to be a “Java evangelist.” He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it.
.


Servlets-_The_New_Application_Architecture04-00.png 397x220

Figure A1: HTML files are used for initial prompting.

Servlets-_The_New_Application_Architecture04-01.png 397x222

Figure A2: HTML is dynamically generated by a JavaServer Page using data from a JavaBean.



Get Customer Information



Customer Number






Figure A3: When the input display is static, there is no need for a JSP.


import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
import denoncourt.*;

public class GetCustomer extends HttpServlet
{

Connection con;

public void init() throws ServletException {

try {

Class.forName("com.ibm.db2.jdbc.app.DB2Driver");

} catch( ClassNotFoundException e) {System.out.println(e);}

try {

con = DriverManager.getConnection("jdbc:db2:*local");

} catch (SQLException e) { System.out.println(e); }

}

public void doGet(HttpServletRequest req, HttpServletResponse resp)

throws ServletException, IOException {

String number = req.getParameter("nbr");

Customer cust = getCustomer(number);

req.setAttribute("Customer", cust);

getServletConfig().getServletContext().

getRequestDispatcher("/listCustomer.jsp").forward(req, resp);

}

Customer getCustomer (String number) {

Customer cust = null;

try {

Statement sql = con.createStatement();

ResultSet rs =

sql.executeQuery("select nbr, name, addr from custmast " +

"where nbr = " + number);

rs.next();

cust = new Customer (

rs.getInt(1), rs.getString(2), rs.getString(3));

} catch (SQLException e) { System.out.println(e);}

return cust;

}

}

Figure A4: A Java servlet handles the user’s request by retrieving data from the database, stuffing that data into a JavaBean, and forwarding control to a JSP.


package denoncourt;

public class Customer {

private int number = 0;

private String name = "default name";

private String address = "default address";

public Customer() {}

public Customer (int number, String name, String address) {

this.number = number;

this.name = name;

this.address = address;

}

public String getName() {return name;}

public String getAddress() {return address;}
}

Figure A5: A JavaBean contains the information obtained by the Java servlet.


class="denoncourt.Customer" />

List Customer

Name:
<%= Customer.getName()%>

Address:
<%= Customer.getAddress()%>

Figure A6: A JSP formats the information contained in a JavaBean by using a combination of HTML and Java syntax.


JSPs Servlets Smart Parameters/View Beans

Input Handled by Servlet Build HTML from View Bean Info

Application Controllers DB2 Access

HTML

Generate User Interface

Forward

Control to JSP

Create View Beans

Figure 1: The new application architecture uses HTML, Java servlets, JavaBeans, and JavaServer Pages.


BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: