JavaServer[tm] Pages Technology FAQs


1. What is the latest version of the JavaServer[tm] Pages (JSP[tm]) Specification and where can I find it?
   
2. What is meant by the JSP and Java[tm] Servlet Reference Implementation?
   
3. What tools are available for testing my JSP technology based applications?
   
4. What tools are available for developing JSP technology based web applications?
   
5. What commercially available tools are there for deploying JSP technology based web applications?
   
6. Are there any JSP tutorials available?
   
7. Are there any training classes available?
   
8. Is there a certification for developers using JSP technology?
   
9. What other technical resources are available?
   
10. How can I get technical support?
    
11. What are the general design rules for creating a page using JavaServer pages technology (JSP page)?
    
12. What are the implicit objects provided by a JSP page?
    
13. What is meant by Page beans, Session beans and Application beans in JSP framework?
    
14. What is the XML syntax of a JSP technology page element?
    
15. What is a custom tag?
    
16. What are Tag libraries and Tag Handlers?
    
17. How can you set a cookie in a JSP page?
    
18. How can we delete a cookie with JSP page?
    
19. How can I avoid caching of JSP page by the browser?
    
20. Can I include static files within a JSP page?
    
21. Can I create dynamic GIFs using JSP technology?
    
22. How to get a client address in a JSP page
    
23. Are there any sample applications available that demonstrate the correct use of JSP pages as web components?

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1. What is the latest version of the JavaServer[tm] Pages (JSP[tm]) Specification and where can I find it?

You can download v1.1 and v1.2 of the JSP specification here.

Version 1.0 of the specification has been archived but is still available for download here.

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2. What is meant by the JSP and Java Servlet Reference Implementation?

The official Reference Implementation for versions 1.1 and 1.2 of the JSP Specification is Tomcat which is produced and controlled by the Apache Software Foundation as part of the Jakarta Project. The mission of the Jakarta Project is to "Provide commercial-quality server solutions based on the Java Platform that are developed in an open and cooperative fashion."

The 3.x versions of Tomcat implement the 1.1 version of the JSP (and Java Servlet 2.2) specification while the 4.x  releases support the JSP 1.2 specification (and Java Servlet 2.3).
To find out which are the latest versions of Tomcat, check here.

The Reference Implementation for version 1.0 of the JSP specification is the JavaServer Web Development Kit v1.0.1 which is available for download from here.
the JavaServer Web Development Kit 1.0.1 is also the Reference Implementation for version 2.1 of the Java Servlet Specification.
As the 1.0 specification has been superseded by the 1.1 Specification, the JavaServer Web Development Kit has not been updated since October, 1999, so it's important to read the release notes before using it.

Note: There is also a Java Servlet Development Kit which is the original Reference Implementation for version 2.1 of the Java Servlet specification, but this does not include support for JSP technology.  

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3. What tools are available for testing my JSP technology based applications?

The Orion Application Server is free for development and for non-commercial deployment but isn't OpenSource. 

Orion Application Server

For commercially available products see the "What commercially available tools are there for deploying JSP technology based web applications?" question in this set of FAQs.  

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4. What tools are available for developing JSP technology based web applications?

Forte[tm] for Java[tm] Enterprise Edition v3.0 (Solaris[tm] Operating Environment, Java platform, Linux and Win32)
Forte for Java Community Edition v3.0 (Solaris[tm] Operating Environment, Java platform, Linux and Win32)
JBuilder5 Professional (Solaris Operating Environment, Linux and Win32)
WebGain VisualCafé Enterprise Edition (Win32)
IBM VisualAge for Java v4.0 Professional/Enterprise (Win32)

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5. What commercially available tools are there for deploying JSP technology based web applications?

Allaire JRun
BEA Systems Web Logic Application Server
Borland Application Server
GemStone/J
HP Bluestone Total-e-Server
IBM WebSphere Application Server
iPlanet[tm] Application Server
Iona IPortal Application Server
Lutris EAS (based on Enhydra)
SilverStream Application Server
Sybase EA Server
Orion Application Server
Persistence Powertier for EJB
Pramati Server
Secant ModelMethods Enterprise Server
Unify eWave Engine and eWave Studio
Versata Logic Server

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6. Are there any JSP tutorials available?

Strangely, JSP technology tutorials are few in number although there are many books that have been specifically written for developers JSP applications. The Java Developer Connection[SM] web site has a tutorial called JavaServer[tm] Pages fundamentals,   which covers the basics of JSP application development but doesn't include anything on Tag Libraries.  A Tag Libraries tutorial is available from the JSP technology Tag Libraries page on the Java Developer Connection[SM] web-site although it's under the heading of "Java Software Tutorial".  You can download the PDF version of the tutorial from here (doesn't include the examples).  This page also includes a link to the Tag Libraries chapter of the book "Core Servlets and JavaServer Pages".

The J2EE[tm] Tutorial also includes a section on JSP technology development and the deployment of web components.

IBM also has a an "Introduction to JavaServer Pages technology" tutorial on their DeveloperWorks site. 

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7. Are there any training classes available?

Sun Educational Services (SunEd) offers several Instructor led and web-based courses that either directly relate to JavaServer Pages technology or cover them within the scope of the J2EE platform or web technologies. Visit the SunEd web site at http://suned.sun.com and navigate to the country where you are located. There you can find details of all of the Java technology courses available in your region. 

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8. Is there a Certification for developers using JSP technology?

IBM has several IBM certifications that require knowledge of JSP technology but are generally more focused on support for their VisualAge and WebSphere products. You can find out more about the IBM certifications by visiting their Application Development Certification web site.

Details of the Sun Certifications can be found here . In order to find out about Sun Certifications in your country got to the Sun Educational Services web site at http://suned.sun.com and use the map to navigate to your local country site.

Also, there is the jCert[tm] initiative which was founded in 1999 by many of the big names in Enterprise Java application development. The aim of the jCert initiative is to promote common standards for validating the skills of developers working with the Java platform. 

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9. What other technical resources are available?

Throughout the Internet, resources for JSP application development abound.  Each of the application server vendors have really good technical resources for not only their products but for JSP technology in general. If you have an application server specific problem it is always a good idea to visit the vendors web site before posting to the JavaServer pages forum.

TheServerSide.com is an excellent J2EE[tm] technology community that also has a forum on which you can discuss JSP technology related issues.

The JavaWorld[tm] publication consistently produces great JSP technology related technical articles as well as covering all other aspects of Java technology. Visit their "Enterprise JavaBeans[tm] " section here .

Quasy H. Mahmoud has also produced an excellent series of articles on web application development with JSP and XML technologies and these have been published on Sun's Java Developer Connection[SM] web site. They are as follows:

Part 1: Fast Track JSP
Part II: JSP technology with XML in Mind
Part III: Developing JSP technology-based Custom Tags   

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10. How can I get Technical Support?

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11. What are the general design rules for creating a page using JavaServer pages technology (JSP page)?

• JSP technology tags are case sensitive.
• Attribute values in tags always appear quoted ; either single or double quotes can be used.
• Any white-space within the documentation is not significant.
• Spaces are NOT allowed between the equals sign& an attribute value.
  
• The character "\" can be used as an escape character in a tag.
• URLs used in JSP technology pages follow Java Servlet conventions, and a URL starting with a "/", called a context relative path, is interpreted with reference to the web application to which the JSP technology page belongs.
• If the URL does not start with a "/" it is interpreted relative to the current JSP technology page.

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12. What are the implicit objects provided by a JSP page?

The implicit objects available in a JSP technology page are:  

• The request object. This represents an HTTP request and is an instance of javax.servlet.http.HttpServletRequest . The request object represents the request that triggered the sevice() invocation. It has request scope.
• The response object. This represents an HTTP response and is an instance of javax.servlet.http.HttpServletResponse . It is legal to set HTTP status codes and headers in the JSP page once output has been sent to the client. It has page scope.
• The pageContext object. This represents the JSP technolgy page and is an instance of the page implementation class that was generated by the JSP technology translator. It is of type javax.Servlet.jsp.PageContext, and has page scope.
• The session object. This represents an HTTP session and is an instance of javax.servlet.http.HttpSession . It has session scope.
• The application object. This represents the servlet context for the web application and is an instance of javax.servlet.ServletContext. It has application scope.
• The out object. This is an object that is used to write output to the browser from the JSP technology page and is an instance of javax.servlet.jsp.JspWriter . The buffer size can be adjusted via the buffer attribute of the page directive.
• The config object. This config object is the ServletConfig for the JSP technology page. It is of type javax.Servlet.ServletConfig and has page scope.
• The page object. This is an object that is used for the instance of the pages's implementation servlet class. It is of type java.lang.Object, and has page scope.
• The exception object. This is an object that is available to the programmer inside a JSP technology error page.

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13. What is meant by Page beans, Session beans and Application beans in JSP technology?

A page bean is a model, with the JSP technology page being the view. Page beans are closely integrated with the JSP technology pages that use them.They will only be used on mulitiple pages if the same content must be presented in different formats. Typically, page beans will define 'getter' methods for each piece of  dynamic content displayed by the corresponding JSP technology page. These getters  may return primitive types, or more complex object types which the JSP technology page will be responsible for displaying. 

Session beans belong to a user's session within an application, not a page. They are not tied to presentation, but help hold references to enterprise resources and other data allowing a user session to maintain and cache state. JSP technology session beans are not directely  concerned with page production, they should be views of or proxies for enterprise middleware, not enterprise middleware themselves.

Application beans are still wider in scope than session beans. They maintain state for all users of a web application. They are used less often than session beans, but can be useful to minimize memory usage and enhance performance, especially when many users require access to some data that is expensive to retrive. Application beans are best used for read-only data. Using them to hold read-write data is a recipe for concurrency problems or synchronization bottlenecks. 

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14. What is the XML syntax of a JSP technology page element?

 

Directives
JSP Syntax:	<%@ directiveName ATTRIBUTES %>
XML-based syntax:	<jsp:directive:directiveName ATTRIBUTES />
Scripting Elements: Declarations
JSP Syntax:	<%! declaration code %>
XML-based syntax:	<jsp:declaration> declaration code</jsp:declaration>
Scripting Elements: Scriplets
JSP Syntax:	<% scriptlet code %>
XML-based syntax:	<jsp:scriptlet> scriptlet code</jsp:scriptlet>
Scripting Elements: Expressions
JSP Syntax:	<% expression code %>
XML-based syntax:	<jsp:expression> expression code</jsp:expression>

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15. What is a custom tag?

Custom tags can:

• Be customized via attributes passed from the calling page
• Access all the objects available to JSP technology pages
• Modify the response generated by the calling page
• Communicate with each other. You can create and initialize a JavaBeans[tm] component, create a variable that refers to that bean in one tag, and then use the bean in another tag.
• Be nested within one another, allowing for complex interactions within a JSP technology page
• Encapsulate both simple and complex behaviors in an easy to use syntax and greatly simplify the readability of JSP technology page

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16. What are Tag Libraries and Tag Handlers?

There are two types of components for a tag library:

• Tag library descriptor file
• Tag handlers

A tag library descriptor (TLD) is an XML document that describes a tag library. A TLD contains information about a library as a whole and about each tag contained in the library. TLDs are used by a JSP technology container to validate the tags and by JSP technology page development tools.

Tag Handler:

A tag handler is an object invoked by a JSP technology container to evaluate a custom tag during the execution of the JSP technology page that references the tag. Tag handler methods are called by the JSP technology page implementation class at various points during the evaluation of the tag.
When the start tag of a custom tag is encountered, the JSP page implementation class calls methods to initialize the appropriate handler and then invokes the handler's doStartTag method. When the custom end tag is encountered, the handler's doEndTag method is invoked. Additional methods are invoked in between when a tag handler needs to interact with the body of the tag. In order to provide a tag handler implementation, you must implement the methods that are invoked at various stages of processing the tag.

A tag handler has access to an API that allows it to communicate with the JSP technology page. The entry point to the API is the page context object through which a tag handler can access to all the other implicit objects (request, session, and application) accessible from a JSP technology page. Implicit objects can have attributes associated with them. Such attributes are accessed using the appropriate set/get]Attribute method. If the tag is nested, a tag handler also has access to the handler (called the parent) associated with the enclosing tag. Tag handlers must implement either the Tag or BodyTag interfaces. Interfaces can be used to take an existing Java technology object and make it a tag handler. For newly created handlers, you can use the TagSupport and BodyTagSupport classes as base classes.

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17. How can you set a cookie in a JSP technology page?

Setting cookies from within a JSP technology page is similar to the way they are done within servlets. For example, the following scriptlet sets a cookie "Hicookie" at the client:  

<%
Cookie Hicookie = new Cookie("aName","aValue");
response.addCookie(Hicookie);
%>

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18. How can we delete a cookie with JSP technology page?

<%
Cookie killHiCookie = new Cookie("Hicookie", null);
killHiCookie.setMaxAge(0);
killHiCookie.setPath("/");
response.addCookie(killHiCookie);
%>

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19. How can I avoid the caching of a JSP technology page by the browser?

<%
response.setHeader("Cache-Control","no-cache");
response.setHeader("pragma","no-cache");
response.setDateHeader ("Expires", "Sun,26 Apl 2001 09:00:00 GMT"); //Date in the past
%>

There are some problems with disabling page caching under IE 5.0, due to the unique buffering. It's a good idea to check the history settings for both Netscape and Internet Explorer browsers.  

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20. How can I include other files or resources within a JSP technology page?

The include directive:

<%@ include file=<filename> %>

<%@ include file="header.html" %>
<%@ include file="banner.html" %>
<%@ include file="tableData.jsp" %>

The include action:

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21. Can I create dynamic GIFs using JSP technology?

Example one:
 

        <img src="<% case(gifNo){

        case 0:%>zero.gif<%;

        break;

        case 1: %>one.gif<%;

        break;

        default: %>default.gif<%;

        } %>" >

Using this piece of code, GIFs can be used dynamically inside a page with JSP technology. In the above code fragment the gifNo is used to decide which GIF image is to be displayed. The gifNo   can be obtained from the request. In Example One, the GIF files have been hard coded into the JSP technology file: a more elegant way to handle this would be to retrieve them at runtime as in Example 2.  

Example Two:
 

    <jsp:useBean id="imageBean" class="package.ImageBean" scope="page" />

    <%

      String imageNo = request.getParameter("ImageNo");

      byte[] jpegArray = imageBean.getJPEG(Integer.parseInt(imageNo));

      response.setContentType("image/jpeg");

      ServletOutputStream op = response.getOutputStream();

      op.write(jpegArray, 0, jpegArray.length);

    %>

In this example the bean imageBean, contains an array of JPEG/GIF images. These could be changed at runtime depending on the occurrence of an event. For example, if the GIF images have to change depending on a user's preference of language or style then the appropriate images could be loaded into the bean and displayed wherever required. Here, as in Example One,  depending on the imageNo parameter which is  passed through the request, the correct JPEG/GIF image is retrived from the array and sent as part of the response to the client. 

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22. How to get client name and address from within a JSP technology page.

 getRemoteAddr(): Returns the Internet Protocol (IP) address of the client that sent the request.

    Returns: String - remote IP address

getRemoteHost(): Returns the fully qualified name of the client that sent the request.

    Returns: String - remote host

These methods can be used within a JSP technology page to output the Hostname and IP address of the client that made the request.

For example:

<%

  out.print( request.getRemoteAddr() );

  out.print( request.getRemoteHost() );

%> 

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23. Are there any sample applications available that demonstrate the correct use of JSP technology pages as web components?

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