Jakarta Server Pages

Last updated
JSP
Filename extension
.jsp, .jspx, .jspf
Internet media type
application/jsp[ citation needed ]
Developed by Eclipse Foundation
Initial release1999;25 years ago (1999)
Latest release
4.0
April 9, 2024;3 months ago (2024-04-09)
Type of format Dynamic web page
Standard JSR 245
Open format?Yes
Website projects.eclipse.org/projects/ee4j.jsp OOjs UI icon edit-ltr-progressive.svg

Jakarta Server Pages (JSP; formerly JavaServer Pages) [1] 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, [2] JSP is similar to PHP and ASP, but uses the Java programming language.

Contents

To deploy and run Jakarta Server 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 Jakarta 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. [3]

Jakarta Server 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. [4]

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. [5]

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

Directives, scriptlets, and expressions, declaration

JSPs use several delimiters for scripting functions. The most basic is <% ... %>, which encloses a JSP scriptlet. A scriptlet is a fragment of Java code [6] that runs 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 <%@ ... %>. [6] [7]

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.

Example

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

<p>Countingtothree:</p><%for(inti=1;i<4;i++){%><p>Thisnumberis<%=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.

Standard JSP Tags

The useBean Tag

The JSP useBean tag enables the developer to access and create a Javabean. [8] Although using the useBean tag looks similar to an HTML tag, all JSP tags for JavaBeans use XML syntax. Therefore the code containing the useBean tag is case-sensitive. [9]

The useBean tag contains several attributes. The id attribute declares the name that is used for gaining access to the bean. The class attribute declares the package and class for the bean. The scope declares the object responsible for storing the bean. The value for the scope defines the duration for which the bean is available for the rest of the java application to use. The scope can be one of the following four values: [9]

  • The page scope implies that the bean is located in the implicitly defined PageContext object, and is only available for the current page. By default, all beans have a scope of page.
  • The request scope implies that the bean can be found in the HttpServletRequest object. This bean can be accessed by all other JSPs and servlets that have access to the current request object.
  • The session scope implies that the bean can be found in the HttpSession object. This bean can be accessed by all other JSPs and servlets that have access to the specified HttpSession object.
  • The application scope implies that the bean can be found in the ServletContext object. This bean can be accessed by all other JSPs and servlets that have access to the specified ServletContext object.

The getProperty and setProperty Tags

After a bean has been created using the useBean tag, the getProperty and setProperty tags can be used for getting and setting the properties of the bean. The JSP getProperty is used to get the property of created bean. The JSP setProperty tag is used to set the properties for a bean. For the getProperty and setProperty tags, the name attribute is used to specify the bean's name. So the name attribute must match the id attribute provided by the useBean tag. [10]

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. [11]

The JSP Expression Language uses a compact syntax which enables the developer to get attributes and JavaBean properties from a given request object. When using EL, a dollar sign ("$") must be added at the beginning of the code. The dollar symbol is followed by an opening brace ("{"), as well as a closing brace ("}"). The code is then written between the opening and closing braces. [12]

Example

The following is 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. [7] Additionally, the technology allows for the creation of custom JSP tag libraries that act as extensions to the standard JSP syntax. [13] One such library is the JSTL. [14]

Jakarta Standard Tag Library

Jakarta Standard Tag Library (JSTL) supports common tasks that must be performed in JSPs. [15] Examples includes iteration and conditionals (the equivalent of "for" and "if" statements in Java). [14]

Out of all the libraries in JSTL, the JSTL core library is most commonly used. A taglib directive must be used to specify the URI of the JSTL core library using a prefix. Although there are many different choices for the prefix, the "c" prefix is commonly used for this library. [16]

XML-compliant JSP

JSP pages may also be written in fully valid XML syntax. [17] Such JSP files commonly use the alternative .jspx file extension, which usually causes the application server to validate the XML syntax.

Since the usual JSP syntax <% ... %> is not valid in XML, a developer must use alternative tags provided by JSP. For example, the common <%@ page .. %> directive may instead be written as a <jsp:directive.page .. /> tag, and tag libraries are imported using XML namespaces, instead of the usual <%@ taglib .. %> tag.

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. [18]

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. [19]

Criticism

According to Joel Murach and Michael Urban, authors of the book "Murach's Java Servlets and JSP", embedding Java code in JSP is generally bad practice. [20] A better approach would be to migrate the back-end logic embedded in the JSP to the Java code in the Servlet. [20] In this scenario, the Servlet is responsible for processing, and the JSP is responsible for displaying the HTML, [20] maintaining a clear separation of concerns.

In 2000, Jason Hunter, author of "Java Servlet Programming" described a number of "problems" with JavaServer Pages. [21] 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). [21] Today, 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

Jakarta Enterprise Beans is one of several Java APIs for modular construction of enterprise software. EJB is a server-side software component that encapsulates business logic of an application. An EJB web container provides a runtime environment for web related software components, including computer security, Java servlet lifecycle management, transaction processing, and other web services. The EJB specification is a subset of the Java EE specification.

<span class="mw-page-title-main">Jakarta EE</span> Set of specifications extending Java SE

Jakarta EE, formerly Java Platform, Enterprise Edition and Java 2 Platform, Enterprise Edition (J2EE), is a set of specifications, extending Java SE with specifications for enterprise features such as distributed computing and web services. Jakarta EE applications are run on reference runtimes, which can be microservices or application servers, which handle transactions, security, scalability, concurrency and management of the components they are deploying.

<span class="mw-page-title-main">Jakarta Servlet</span> Jakarta EE programming language class

A Jakarta Servlet, formerly 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 Jakarta 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. A web container handles requests to servlets, Jakarta Server Pages (JSP) files, and other types of files that include server-side code. The Web container creates servlet instances, loads and unloads servlets, creates and manages request and response objects, and performs other servlet-management tasks. A web container implements the web component contract of the Jakarta EE architecture. This architecture specifies a runtime environment for additional web components, including security, concurrency, lifecycle management, transaction, deployment, and other services.

<span class="mw-page-title-main">Apache Tomcat</span> Java-based HTTP web server environment

Apache Tomcat is a free and open-source implementation of the Jakarta Servlet, Jakarta Expression Language, and WebSocket technologies. It provides a "pure Java" HTTP web server environment in which Java code can also run. Thus it is a Java web application server, although not a full JEE application server.

<span class="mw-page-title-main">Adobe ColdFusion</span> Rapid Web app development platform

Adobe ColdFusion is a commercial rapid web-application development computing 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 had become a full platform that included an IDE in addition to a full scripting language.

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

<span class="mw-page-title-main">Apache Struts 1</span> 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.

In computing, Oracle Application Development Framework, usually called Oracle ADF, provides a Java framework for building enterprise applications. It provides visual and declarative approaches to Java EE development. It supports rapid application development based on ready-to-use design patterns, metadata-driven and visual tools.

Apache Velocity first released in April 2001, is a Java-based template engine that provides a template language to reference objects defined in Java code. It aims to ensure clean separation between the presentation tier and business tiers in a Web application.

The Jakarta Standard Tag Library 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.

The Spring Framework is an application framework and inversion of control container for the Java platform. The framework's core features can be used by any Java application, but there are extensions for building web applications on top of the Java EE platform. The framework does not impose any specific programming model.. The framework has become popular in the Java community as an addition to the Enterprise JavaBeans (EJB) model. The Spring Framework is free and open source software.

Grails is an open source web application framework that uses the Apache Groovy programming language. It is intended to be a high-productivity framework by following the "coding by convention" paradigm, providing a stand-alone development environment and hiding much of the configuration detail from the developer.

<span class="mw-page-title-main">Apache MyFaces</span> Open-source implementation of JavaServer Faces

Apache MyFaces is an Apache Software Foundation project that creates and maintains an open-source JavaServer Faces implementation, along with several libraries of JSF components that can be deployed on the core implementation. The project is divided into several sub-projects:

The Jakarta Expression Language is a special purpose programming language mostly used in Jakarta EE web applications for embedding and evaluating expressions in web pages. The specification writers and expert groups of the Java EE 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 Jakarta Faces. 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.

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.

References

  1. ↑ Matthew Tyson (September 9, 2022). "What is JSP? Introduction to Jakarta Server Pages". InfoWorld. Retrieved May 30, 2024.
  2. ↑ "FoRK Archive: Sun JSP 1.0 *not* available". www.xent.com.
  3. ↑ The Life Cycle of a JSP Page (Sun documentation)
  4. ↑ Seshadri, Govind (December 29, 1999). "Understanding JavaServer Pages Model 2 architecture". JavaWorld . Retrieved 2020-07-17.
  5. ↑ "OutputStream already obtained (JSP forum at Coderanch)". coderanch.com.
  6. 1 2 Murach & Urban 2014, pp. 180–182, §2 Essential servlet and JSP skills - How to use JSP tags.
  7. 1 2 JSP 1.2 Syntax Reference
  8. ↑ Murach & Urban 2014, pp. 198, §2 Essential servlet and JSP skills - Summary.
  9. 1 2 Murach & Urban 2014, pp. 186–187, §2 Essential servlet and JSP skills - How to code the useBean tag.
  10. ↑ Murach & Urban 2014, pp. 188, §2 Essential servlet and JSP skills - How to code the getProperty and setProperty tags.
  11. ↑ The Unified Expression Language (Sun Developer Network)
  12. ↑ Murach & Urban 2014, pp. 176–177, §2 Essential servlet and JSP skills - How to use EL to get attributes and JavaBean properties.
  13. ↑ Tag Libraries Tutorial - What is a Tag Library? (Sun) Archived April 19, 2012, at the Wayback Machine
  14. 1 2 "JavaServer Pages Standard Tag Library - The Java EE 5 Tutorial". docs.oracle.com.
  15. ↑ Murach & Urban 2014, pp. 270–273, §2 Essential servlet and JSP skills -An Introduction to JSTL.
  16. ↑ Murach & Urban 2014, pp. 178, §2 Essential servlet and JSP skills - How to enable the core JSTL library.
  17. ↑ "The Java EE 5 Tutorial, Chapter 6 JavaServer Pages Documents". oracle.com. Retrieved 2022-07-27.
  18. ↑ "IBM Docs". www.ibm.com.
  19. ↑ "SyBooks Online". infocenter.sybase.com.
  20. 1 2 3 Murach & Urban 2014, pp. 46–47, §1 Get started right - The JSP for the second page.
  21. 1 2 The Problems with JSP (January 25, 2000)

Works cited

Further reading

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