Web Application Development with JSP and XML
Part I: Fast Track JSP

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If you have had the opportunity to build web applications using technologies such as Common Gateway Interface (CGI) and servlets, you are accustomed to the idea of writing a program to generate the whole page (the static and the dynamic part) using that same program. If you are looking for a solution in which you can separate the two parts, look no further. JavaServer Pages (JSP) are here.

JSP pages allow you to separate front-end presentation from business logic (middle and back-end tiers). It is a great Rapid Application Development (RAD) approach to Web applications. This series of articles provides a hands-on tutorial explaining how to develop modern Web applications for today's and tomorrow's market. This series begins with this article, which explains the concepts and benefits of JSP technology, and then shows you how to utilize this exciting technology, and how to create reusable components for handling forms.

The Dynamic Web

The Web has evolved from a network-based hypermedia distributed information system offering static information to a marketplace for selling and buying goods and services. The increasingly sophisticated applications to enable this marketplace require a technology for presenting dynamic information.

First generation solutions included CGI, which is a mechanism for running external programs through a web server. The problem with CGI scripts is scalability; a new process is created for every request.

Second generation solutions included web server vendors providing plug-ins and APIs for their servers. The problem is that their solutions were specific to their server products. For example, Microsoft provided Active Server Pages (ASP) that made it easier to create dynamic content. However, their solution only worked with Microsoft IIS or Personal Web Server. Therefore, if you wanted to use ASP you had to commit yourself to Microsoft products and you would not be enjoying the freedom of selecting your favorite web server and operating system!

Another second generation technology that is quite popular in enterprise computing is servlets. Servlets make it easier to write server-side applications using Java technology. The problem with either CGI or servlets, however, is that you have to follow the write, compile, and deploy life cycle.

JSP pages are a third generation solution that can be combined easily with some second generation solutions, creating dynamic content, and making it easier and faster to build web-based applications that work with a variety of other technologies: web servers, web browsers, application servers and other development tools.

JavaServer Pages (JSP)

The JSP technology is an open, freely available specification developed by Sun Microsystems as an alternative to Microsoft's Active Server Pages (ASP) technology, and a key component of the Java 2 Enterprise Edition (J2EE) specification. Many of the commercially available application servers (such as BEA WebLogic, IBM WebSphere, Live JRun, Orion, and so on) already support JSP technology.

JSP versus ASP

JSP and ASP deliver similar functionality. They both use tags to allow embedded code in an HTML page, session tracking, and database connection. Some of the trivial differences are:

• ASP pages are written in VBScript and JSP pages are written in the Java programming language. Therefore, JSP pages are platform-independent and ASP pages are not.
• JSP pages use JavaBeans technology as the component architecture and ASP pages use ActiveX components.

Beyond these trivial differences, there are a number of important differences that may help you in choosing a technology for your organization:

• Speed and Scalability: Although ASP pages are cached, they are always interpreted. By contrast, JSP pages are compiled into Java servlets and loaded into memory the first time they are called, and executed for all subsequent calls. This gives JSP pages aspeed and scalability advantage over ASP pages.
• Extensible Tags: JSP pages have an advanced feature known as extensible tags. This mechanism enables developers to create custom tags. In other words, extensible tags allow you to extend the JSP pages tag syntax. You cannot do this with ASP pages.
• Freedom of Choice: Unless you install Chili!Soft ASP, ASP pages work only with Microsoft IIS and Personal Web Server. Using ASP pages requires a commitment to Microsoft products, while JSP pages do not tie you to any specific web server or operating system. JSP pages are becoming a widely supported standard.

For a more detailed comparison between JSP pages and ASP pages, see Comparing JSP and ASP.

Software Environment

To run JSP pages, you need a web server with a web container that conforms to JSP and servlet specifications. The web container executes on the web server and manages the execution of all JSP pages and servlets running on that web server. Tomcat 3.2.1 is a complete reference implementation for the Java Servlet 2.2 and JSP 1.1 specifications. Download and install binary versions of Tomcat.

To configure Tomcat:

• Set the environment variable JAVA_HOME to point to the root directory of your Java 2 Standard Edition (J2SE) installation.
• Set the TOMCAT_HOME environment variable to point to the root directory of your Tomcat installation.
• To start Tomcat, use TOMCAT_HOME/bin/startup.bat for windows or startup.sh for UNIX.
  By default, it will start listening on port 8080.
• Save your .jsp files in TOMCAT_HOME/webapps/examples/jsp and your JavaBeans classes in TOMCAT_HOME/webapps/examples/web-inf/classes.

Note: If you work under Windows, you may get an Out of space environment error when you try to start Tomcat. There are two ways to fix this: either change the initial memory setting of the DOS window to a value greater than 3200 OR edit the config.sys file and add the following line: SHELL=c:\PATHTO\command.com /E:4096 /P.

How JSP Pages Work

A JSP page is basically a web page with traditional HTML and bits of Java code. The file extension of a JSP page is ".jsp" rather than ".html" or ".htm", and that tells the server that this page requires special handling that will be accomplished by a server extension or a plug-in. Here is a simple example:

Sample 1: date.jsp

     
<HTML>
<HEAD>
<TITLE>JSP Example</TITLE>
</HEAD>
<BODY BGCOLOR="ffffcc">
<CENTER>
<H2>Date and Time</H2>
<%  
java.util.Date today = new java.util.Date();
out.println("Today's date is: "+today);
%>
</CENTER>     
</BODY>     
</HTML>     

This example contains traditional HTML and some Java code. The tag <% identifies the beginning of a scriptlet, and the %> tag identifies the end of a scriptlet. When date.jsp is requested from a web browser, you see something similar to Figure 1.

Figure 1: Requesting date.jsp

Behind the Scenes

When this page (date.jsp) is called, it will be compiled (by the JSP engine) into a java servlet. At this point the servlet is handled by the servlet engine just like any other servlet. The servlet engine then loads the servlet class (using a class loader) and executes it to create dynamic HTML to be sent to the browser, as shown in Figure 2. For this example, the servlet creates a Date object and writes it as a string to the out object, which is an output stream to the browser.

Figure 2: Request/Response Flow when Calling a JSP

The next time the page is requested, the JSP engine executes the already-loaded servlet unless the JSP page has changed, in which case it is automatically recompiled into a servlet and executed.

Scripting Elements

In the date.jsp example the full Date class name is used including the package name, which may become tedious. If you want to create an instance of Date simply by using: Date today = new Date(); without having to specify the full class path use the page directive as follows:

Sample 2 :date2.jsp

     
<%@page import="java.util.*" %>
<HTML>  
<HEAD> 
<TITLE>JSP Example</TITLE>  
</HEAD> 
<BODY BGCOLOR="ffffcc">
<CENTER> 
<H2>Date and Time</H2>  
<% 
java.util.Date today = new java.util.Date();
out.println("Today's date is: "+today);
%>
</CENTER>
</BODY> 
</HTML>

Yet, another way of doing the same thing using the <%= tag is by writing:

Sample 3:date3.jsp

     
<%@page import="java.util.*" %>     
<HTML>     
<HEAD>     
<TITLE>JSP Example</TITLE>     
</HEAD>     
<BODY BGCOLOR="#ffffcc">     
<CENTER>     
<H2>Date and Time</H2>     
Today's date is: <%= new Date() %>     
</CENTER>     
</BODY>     
</HTML>     

As you can see, the same thing can be accomplished using different tags and techniques. There are several JSP scripting elements. Here are some conventional rules that will help you use JSP scripting elements effectively:

• Use <% ... %> to handle declarations, expressions, or any other type of valid snippet of code. Sample 1 above is an example.
• Use the page directive as in <%@page ... %> to define the scripting language. Also, it can be used to specify import statements. Here is an example:
  <%@page language="java" import="java.util.*" %>.
• Use <%! .... %> to declare variables or methods. For example:
  <%! int x = 10; double y = 2.0; %>.
• Use <%= ... %> to define an expression and cast the result as a String. For example:
  <%= a+b %> or <%= new java.util.Date() %>.
• Use the include directive as in <%@ include ... %> to insert the contents of another file in the main JSP file. For example:
  <%@include file="copyright.html" %>.

Handling Forms

One of the most common parts of ecommerce applications is an HTML form where the user enters some information such as name and address. Using JSP, the form's data (the information the user enters in the form) gets stored in the request object that is sent from the browser to the JSP container. The request is processed and the result is sent through the response object back to the browser. These two objects are implicitly available to you.

To demonstrate how to handle HTML forms using JSP, here is an example form with two fields: one for name and the other for email. As you can see, the HTML form is defined in a JSP source file. The request.getParameter method is being used to retrieve data from the form into variables created using JSP tags.

The process.jsp page prints either a form or the information provided by the user depending on the values of the form's fields. If the form's values are null the form is displayed, otherwise, the information provided by the user is displayed. Note that the form is created and being handled by code in the same JSP file.

Sample 4: process.jsp

     
<HTML>     
<HEAD>     
<TITLE>Form Example</TITLE>     
</HEAD>     
<BODY BGCOLOR="#ffffcc">     
<% if (request.getParameter("name")==
null && request.getParameter("email")
 == null) { %>     
<CENTER>     
<H2>User Info Request Form</H2>     
<FORM METHOD="GET" ACTION="/developer/technicalArticles/xml/WebAppDev/process.jsp">     
<P>     
Your name: <input type="text" name=
"name" size=26>     
<P>     
Your email: <input type="text" name=
"email" size=26>     
<P>     
<input type="submit" value="Process">     
</FORM>     
</CENTER>     
<% } else { %>     
<%! String name, email; %>     
<%     
name = request.getParameter("name");     
email = request.getParameter("email");     
%>     
<P>     
<B>You have provided the following 
info</B>:     
<P>     
<B>Name</B>: <%= name %><P>     
<B>Email</B>: <%= email %>     
<% } %>     
</BODY>     
</HTML>     

If process.jsp is requested from a web server, you see something similar to Figure 3.

Figure 3: process.jsp loaded

Enter your name and email and click on Process to submit the form for processing, and you see something similar to Figure 4.

Figure 4: Form is processed

Reusable Components

The above example form is simple in the sense that there is not much code involved. When more code is involved, then it is important not to mix business logic with front end presentation in the same file. Separating business logic from presentation permits changes to either side without affecting the other. However, production JSP code should be limited to front end presentation. So, how do you implement the business logic part?

That is where JavaBeans come in to play. This technology is a portable, platform-independent component model that lets developers write components and reuse them everywhere. In the context of JSP, JavaBeans contain business logic that returns data to a script on a JSP page, which in turn formats the data returned from the JavaBean component for display by the browser. A JSP page uses a JavaBean component by setting and getting the properties that it provides.

What are the Benefits

There are several benefits to using JavaBeans to augment JSP pages:

• Reusable components: different applications will be able to reuse the components.
• Separation of business logic and presentation logic: you can change the way data is displayed without affecting business logic.
• Protecting your intellectual property by keeping source code secure.

Example: Using JavaBeans with JSP

Now, let's see how to modify the process.jsp example above to use JavaBeans. In the above form these are two fields: name and email. In JavaBeans, these are called properties. So, first you write a JavaBean component with setX and getX methods, where X is the property name. For example, if you have get and set methods: setName and getName then you have a property known as name. Sample 5 shows a FormBean component.

Good components must be able to interoperate with other components from different vendors. Therefore, to achieve component reuse, there are two important rules (which are imposed by the JavaBeans architecture) to follow:

1. Your bean class must provide a constructor with no arguments so it can be created using Beans.instantiate.
2. Your bean class must support persistence by implementing the interface Serializable or Externalizable.

Sample 5: FormBean.java

     
package userinfo;     
import java.io.*;     
public class FormBean implements Serializable {     
  private String name;     
  private String email;     
  public FormBean() {     
   name = null;     
   email = null;     
  }     
  public void setName(String name) {     
   this.name = name;     
  }     
  public String getName() {     
   return name;     
  }     
  public void setEmail(String email) {     
   this.email = email;     
  }     
  public String getEmail() {     
   return email;     
  }     
}     

In order to use the FormBean component in the JSP file, you need to instantiate the bean component. This is done using the <jsp:useBean> tag. The next line <jsp:setProperty> is executed when the bean is instantiated, and used to initialize the bean's properties. In this case, both properties (name and email) are set using a single statement. Alternatively, it is possible to set the properties one at a time, but first you need to retrieve the form's date. Here is an example of how you would set the name property:

     
<%! String yourname, youremail; %>     
<% yourname = 
request.getParameter("name"); %>     
<jsp:setProperty name=
"formbean" property="name" 
value="<%=yourname%>"/>     

Once the properties have been initialized with data retrieved from the form, property values are retrieved for presentation using <jsp:getProperty> in the else part, as shown in Sample 6.

Sample 6: process2.jsp

     
<jsp:useBean id="formbean" class=
"userinfo.FormBean"/>
<jsp:setProperty name="formbean" property=
"*"/>    
<HTML> 
<HEAD>
<TITLE>Form Example</TITLE>
</HEAD>
<BODY BGCOLOR="#ffffcc">
<% if (request.getParameter("name")==null
 && request.getParameter("email") == null) { %>
<CENTER>
<H2>User Info Request Form </H2>
<form method="GET" action="/developer/technicalArticles/xml/WebAppDev/process2.jsp">
<P>
Your name: <input type="text" name=
"name" size=27>
<p>     
Your email: <input type="text" name=
"email" size=27>    
<P>     
<input type="submit" value="Process">
</FORM>
</CENTER>
<% } else { %>
<P>
<B>You have provided the following info</B>: 
<P>     
<B>Name</B>: <jsp:getProperty name=
"formbean"
property="name"/>     
<P>     
<B>Email</B>: <jsp:getProperty
name="formbean" property="email"/> 
<% } %>     
</BODY>     
</HTML>     

Conclusion

Developers interested in developing quality production web applications should familiarize themselves with technologies that are applicable not only for today's market but tomorrow's as well, namely JSP and XML. The next article will discuss the capabilities that the JSP technology provides that are ideally suited for working with XML; and show you how to effectively use JSP with XML. JSP and XML make an excellent combination for web applications that share information, because JSP pages have XML support built right into them in the form of JSP custom tag libraries. Stay tuned for more information on this in the next article in this series.

For more information

JSP
Tomcat
Comparing JSP and ASP

About the Author

Qusay H. Mahmoud provides Java consulting and training services. Qusay has published dozens of articles on Java, and is the author of Distributed Programming with Java (Manning Publications, 1999).