JavaServer Pages

Last updated
JSP
Filename extension .jsp, .jspx, .jspf
Internet media type application/jsp
Latest release
2.3
Standard JSR 245
Website JavaServer Pages Technology

JavaServer Pages (JSP) is a collection of technologies that helps software developers create dynamically generated web pages based on HTML, XML, SOAP, or other document types. Released in 1999 by Sun Microsystems, [1] JSP is similar to PHP and ASP, but uses the Java programming language.

Contents

To deploy and run JavaServer Pages, a compatible web server with a servlet container, such as Apache Tomcat or Jetty, is required.

Overview

The JSP Model 2 architecture. JSP Model 2.svg
The JSP Model 2 architecture.

Architecturally, JSP may be viewed as a high-level abstraction of Java servlets. JSPs are translated into servlets at runtime, therefore JSP is a Servlet; each JSP servlet is cached and re-used until the original JSP is modified. [2]

JavaServer Pages can be used independently or as the view component of a server-side model–view–controller design, normally with JavaBeans as the model and Java servlets (or a framework such as Apache Struts) as the controller. This is a type of Model 2 architecture. [3]

JSP allows Java code and certain predefined actions to be interleaved with static web markup content, such as HTML. The resulting page is compiled and executed on the server to deliver a document. The compiled pages, as well as any dependent Java libraries, contain Java bytecode rather than machine code. Like any other .jar or Java program, code must be executed within a Java virtual machine (JVM) that interacts with the server's host operating system to provide an abstract, platform-neutral environment.

JSPs are usually used to deliver HTML and XML documents, but through the use of OutputStream, they can deliver other types of data as well. [4]

The Web container creates JSP implicit objects like request, response, session, application, config, page, pageContext, out and exception. JSP Engine creates these objects during translation phase.

Syntax

JSP pages use several delimiters for scripting functions. The most basic is <% ... %>, which encloses a JSP scriptlet. A scriptlet is a fragment of Java code that is run when the user requests the page. Other common delimiters include <%= ... %> for expressions, where the scriptlet and delimiters are replaced with the result of evaluating the expression, and directives, denoted with <%@ ... %>. [5]

Java code is not required to be complete or self-contained within a single scriptlet block. It can straddle markup content, provided that the page as a whole is syntactically correct. For example, any Java if/for/while blocks opened in one scriptlet must be correctly closed in a later scriptlet for the page to successfully compile. This allows code to be intermingled and can result in poor programming practices.

Content that falls inside a split block of Java code (spanning multiple scriptlets) is subject to that code. Content inside an if block will only appear in the output when the if condition evaluates to true. Likewise, content inside a loop construct may appear multiple times in the output, depending upon how many times the loop body runs.

The following would be a valid for loop in a JSP page:

<p>Counting to three:</p><%for(inti=1;i<4;i++){%><p>This number is <%=i%>.</p><%}%><p>OK.</p>

The output displayed in the user's web browser would be:

Counting to three:  This number is 1.  This number is 2.  This number is 3.  OK.

Expression Language

Version 2.0 of the JSP specification added support for the Expression Language (EL), used to access data and functions in Java objects. In JSP 2.1, it was folded into the Unified Expression Language, which is also used in JavaServer Faces. [6]

An example of EL syntax:

The value of "variable" in the object "javabean" is ${javabean.variable}.

Additional tags

The JSP syntax add additional tags, called JSP actions, to invoke built-in functionality. [5] Additionally, the technology allows for the creation of custom JSP tag libraries that act as extensions to the standard JSP syntax. [7] One such library is the JSTL, with support for common tasks such as iteration and conditionals (the equivalent of "for" and "if" statements in Java.) [8]

Compiler

A JavaServer Pages compiler is a program that parses JSPs, and transforms them into executable Java Servlets. A program of this type is usually embedded into the application server and run automatically the first time a JSP is accessed, but pages may also be precompiled for better performance, or compiled as a part of the build process to test for errors. [9]

Some JSP containers support configuring how often the container checks JSP file timestamps to see whether the page has changed. Typically, this timestamp would be set to a short interval (perhaps seconds) during software development, and a longer interval (perhaps minutes, or even never) for a deployed Web application. [10]

Criticism

In 2000, Jason Hunter, author of "Java Servlet Programming" described a number of "problems" with JavaServer Pages. [11] Nevertheless, he wrote that while JSP may not be the "best solution for the Java Platform" it was the "Java solution that is most like the non-Java solution," by which he meant Microsoft's Active Server Pages. Later, he added a note to his site saying that JSP had improved since 2000, but also cited its competitors, Apache Velocity and Tea (template language).[ citation needed ] Today there are several alternatives and a number of JSP-oriented pages in larger web apps are considered to be technical debt.

See also

Servlet containers

Java-based template alternatives

Related Research Articles

Java servlet Java programming language class

A Java servlet is a Java software component that extends the capabilities of a server. Although servlets can respond to many types of requests, they most commonly implement web containers for hosting web applications on web servers and thus qualify as a server-side servlet web API. Such web servlets are the Java counterpart to other dynamic web content technologies such as PHP and ASP.NET.

The Jakarta Project created and maintained open source software for the Java platform. It operated as an umbrella project under the auspices of the Apache Software Foundation, and all Jakarta products are released under the Apache License. As of December 21, 2011 the Jakarta project was retired because no subprojects were remaining.

A web container is the component of a web server that interacts with Java servlets. A web container is responsible for managing the lifecycle of servlets, mapping a URL to a particular servlet and ensuring that the URL requester has the correct access-rights.

Apache Tomcat an implementation of the Java Servlet, JavaServer Pages, Java Expression Language and Java WebSocket technologies

Apache Tomcat is an open-source implementation of the Java Servlet, JavaServer Pages, Java Expression Language and WebSocket technologies. Tomcat provides a "pure Java" HTTP web server environment in which Java code can run.

Adobe ColdFusion is a commercial rapid web-application development platform created by J. J. Allaire in 1995. ColdFusion was originally designed to make it easier to connect simple HTML pages to a database. By version 2 (1996), it became a full platform that included an IDE in addition to a full scripting language.

JavaServer Faces Java specification for building component-based user interfaces for web applications

JavaServer Faces (JSF) is a Java specification for building component-based user interfaces for web applications and was formalized as a standard through the Java Community Process being part of the Java Platform, Enterprise Edition. It is also a MVC web framework that simplifies construction of user interfaces (UI) for server-based applications by using reusable UI components in a page.

Apache Struts 1 open-source web application framework

Apache Struts 1 is an open-source web application framework for developing Java EE web applications. It uses and extends the Java Servlet API to encourage developers to adopt a model–view–controller (MVC) architecture. It was originally created by Craig McClanahan and donated to the Apache Foundation in May 2000. Formerly located under the Apache Jakarta Project and known as Jakarta Struts, it became a top-level Apache project in 2005.

JSP model 2 architecture

JSP Model 2 is a complex design pattern used in the design of Java Web applications which separates the display of content from the logic used to obtain and manipulate the content. Since Model 2 drives a separation between logic and display, it is usually associated with the model–view–controller (MVC) paradigm. While the exact form of the MVC "Model" was never specified by the Model 2 design, a number of publications recommend a formalized layer to contain MVC Model code. The Java BluePrints, for example, originally recommended using EJBs to encapsulate the MVC Model.

Apache Axis

Apache Axis is an open-source, XML based Web service framework. It consists of a Java and a C++ implementation of the SOAP server, and various utilities and APIs for generating and deploying Web service applications. Using Apache Axis, developers can create interoperable, distributed computing applications. Axis development takes place under the auspices of the Apache Software Foundation.

mod_jk is an Apache module used to connect the Tomcat servlet container with web servers such as Apache, iPlanet, Sun ONE and even IIS using the Apache JServ Protocol.

The JavaServer Pages Standard Tag Library (JSTL) is a component of the Java EE Web application development platform. It extends the JSP specification by adding a tag library of JSP tags for common tasks, such as XML data processing, conditional execution, database access, loops and internationalization.

In software engineering, a WAR file is a file used to distribute a collection of JAR-files, JavaServer Pages, Java Servlets, Java classes, XML files, tag libraries, static web pages and other resources that together constitute a web application.

eRuby is a templating system that embeds Ruby into a text document. It is often used to embed Ruby code in an HTML document, similar to ASP, JSP and PHP and other server-side scripting languages. The templating system of eRuby combines the ruby code and the plain text to provide flow control and variable substitution, thus making it easy to maintain.

The Java Unified Expression Language is a special purpose programming language mostly used in Java web applications for embedding expressions into web pages. The Java specification writers and expert groups of the Java web-tier technologies have worked on a unified expression language which was first included in the JSP 2.1 specification (JSR-245), and later specified by itself in JSR-341, part of Java EE 7.

In computing, Facelets is an open-source Web template system under the Apache license and the default view handler technology for JavaServer Faces (JSF). The language requires valid input XML documents to work. Facelets supports all of the JSF UI components and focuses completely on building the JSF component tree, reflecting the view for a JSF application.

Java view technologies and frameworks are web-based software libraries that provide the user interface, or "view-layer", of Java web applications. Such application frameworks are used for defining web pages and handling the HTTP requests (clicks) generated by those web pages. As a sub-category of web frameworks, view-layer frameworks often overlap to varying degrees with web frameworks that provide other functionality for Java web applications.

ZK is an open-source Ajax Web application framework, written in Java, that enables creation of graphical user interfaces for Web applications with little required programming knowledge.

Jspx-bay

jspx-bay, commonly referred to as jspx, is a free open source pure Java web RAD framework. Jspx should not be confused with other technologies using the same name like Oracle Application Framework and XML JSP.

Thymeleaf is a Java XML/XHTML/HTML5 template engine that can work both in web (servlet-based) and non-web environments. It is better suited for serving XHTML/HTML5 at the view layer of MVC-based web applications, but it can process any XML file even in offline environments. It provides full Spring Framework integration.

Apache Attic is a project of Apache Software Foundation to provide process and solutions to make it clear when an Apache project has reached its end-of-life. The Attic project was created in November 2008. Also the retired projects can be retained.

References

  1. ↑ Mailing list archive: "Sun JSP 1.0 *not* available"
  2. ↑ The Life Cycle of a JSP Page (Sun documentation)
  3. ↑ Understanding JavaServer Pages Model 2 architecture (JavaWorld)
  4. ↑ Forum thread (JavaRanch): OutputStream already obtained
  5. 1 2 JSP 1.2 Syntax Reference
  6. ↑ The Unified Expression Language (Sun Developer Network)
  7. ↑ Tag Libraries Tutorial - What is a Tag Library? (Sun) Archived April 19, 2012, at the Wayback Machine
  8. ↑ JSTLs documentation (Oracle) bb
  9. ↑ IBM WebSphere 6.0.2 documentation
  10. ↑ Sybase EAServer 5.0 documentation
  11. ↑ The Problems with JSP (January 25, 2000)

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.