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JavaServer Pages Overview

JavaServer Pages (JSP) technology enables Web developers and designers to rapidly develop and easily maintain, information-rich, dynamic Web pages that leverage existing business systems. As part of the Java technology family, JSP technology enables rapid development of Web-based applications that are platform independent. JSP technology separates the user interface from content generation, enabling designers to change the overall page layout without altering the underlying dynamic content.

Benefits for Developers

If you are a Web page developer or designer who is familiar with HTML, you can: Use JSP technology without having to learn the Java language: You can use JSP technology without learning how to write Java scriplets. Although scriptlets are no longer required to generate dynamic content, they are still supported to provide backward compatibility.

Extend the JSP language: Java tag library developers and designers can extend the JSP language with "simple tag handlers," which utilize a new, much simpler and cleaner, tag extension API. This spurs the growing number of pluggable, reusable tag libraries available, which in turn reduces the amount of code needed to write powerful Web applications.

Easily write and maintain pages: The JavaServer Pages Standard Tag Library(JSTL) expression language is now integrated into JSP technology and has been upgraded to support functions. The expression language can now be used instead of scriptlet expressions.

JSP Technology and Java Servlets

JSP technology uses XML-like tags that encapsulate the logic that generates the content for the page. The application logic can reside in server-based resources (such as JavaBeans component architecture) that the page accesses with these tags. Any and all formatting (HTML or XML) tags are passed directly back to the response page. By separating the page logic from its design and display and supporting a reusable component-based design, JSP technology makes it faster and easier than ever to build Web-based applications.

JavaServer Pages technology is an extension of theJava Servlet technology. Servlets are platform-independent, server-side modules that fit seamlessly into a Web server framework and can be used to extend the capabilities of a Web server with minimal overhead, maintenance, and support. Unlike other scripting languages, servlets involve no platform-specific consideration or modifications; they are application components that are downloaded, on demand, to the part of the system that needs them. Together, JSP technology and servlets provide an attractive alternative to other types of dynamic Web scripting/programming by offering: platform independence; enhanced performance; separation of logic from display; ease of administration; extensibility into the enterprise; and, most importantly, ease of use.

Today servlets are a popular choice for building interactive Web applications. Third-party servlet containers are available for Apache Web Server, Microsoft IIS,

and others. Servlet containers are usually a component of Web and application servers, such as BEA WebLogic Application Server, IBM WebSphere,Sun Java System Web Server, Sun Java System Application Server, and others.

Community Background

The JSP specification is the product of industry-wide collaboration with industry leaders in the enterprise software and tools markets, led by Sun Microsystems. Sun has made the JSP specification freely available to the developer community, with the goal that every Web server and application server will support the JSP interface. JSP pages share the "Write Once, Run Anywhere" advantages of Java technology. JSP technology is a key component in the Java 2 Platform, Enterprise Edition, Sun's highly scalable architecture for enterprise applications.

JSP Technology in the Java EE 5 Platform

The focus of Java EE 5 has been ease of development by making use of Java language annotations that were introduced by J2SE 5.0. JSP 2.1 supports this goal by defining annotations for dependency injection on JSP tag handlers and context listeners. Another key concern of the Java EE 5 specification has been the alignment of its webtier technologies, namely JavaServer Pages (JSP), JavaServer Faces (JSF), and JavaServer Pages Standard Tag Library (JSTL).

The outcome of this alignment effort has been the Unified Expression Language (EL), which integrates the expression languages defined by JSP 2.0 and JSF 1.1.

The main key additions to the Unified EL that came out of tbe alignment work have been:

A pluggable API for resolving variable references into Java objects and for resolving the properties applied to these Java objects,

Support for deferred expressions, which may be evaluated by a tag handler when needed, unlike their regular expression counterparts, which get evaluated immediately when a page is executed and rendered, and

Support for lvalue expression, which appear on the left hand side of an assignment operation. When used as an lvalue, an EL expression represents a reference to a data structure, for example: a JavaBeans property, that is assigned some user input.

The new Unified EL is defined in its own specification document, which is delivered along with the JSP 2.1 specification.

Thanks to the Unified EL, JSTL tags, such as the JSTL iteration tags, can now be used with JSF components in an intuitive way.

Java Servlet Technology Overview

Servlets are the Java platform technology of choice for extending and enhancing Web servers. Servlets provide a component-based, platform-independent method for building Web-based applications, without the performance limitations of CGI programs. And unlike proprietary server extension mechanisms (such as the Netscape Server API or Apache modules), servlets are server- and platform-independent. This leaves you free to select a "best of breed" strategy for your servers, platforms, and tools.

Servlets have access to the entire family of Java APIs, including the JDBC API to

access enterprise databases. Servlets can also access a library of HTTP-specific calls and receive all the benefits of the mature Java language, including portability, performance, reusability, and crash protection.

Today servlets are a popular choice for building interactive Web applications. Third-party servlet containers are available for Apache Web Server, Microsoft IIS, and others. Servlet containers are usually a component of Web and application servers, such as BEA WebLogic Application Server, IBM WebSphere, Sun Java System Web Server, Sun Java System Application Server, and others.

You might want to check out the latest information on JavaServer Pages (JSP)technology. JSP technology is an extension of the servlet technology created to support authoring of HTML and XML pages. It makes it easier to combine fixed or static template data with dynamic content. Even if you're comfortable writing servlets, there are several compelling reasons to investigate JSP technology as a complement to your existing work.

JavaBeans

JavaBeans technology is the component architecture for the Java 2 Platform, Standard Edition (J2SE). Components (JavaBeans) are reusable software programs that you can develop and assemble easily to create sophisticated applications. JavaBeans technology is based on the JavaBeans specification.

The Bean Builder

The Bean Builder is a simple component assembler that demonstrates the visual construction of applications using component assembly mechanisms.

JavaBeans Activation Framework (JAF)

JAF lets you take advantage of standard services to: determine the type of an arbitrary piece of data; encapsulate access to it; discover the operations available on it; and instantiate the appropriate bean to perform the operation(s).

The Java 2 Enterprise Edition (J2EE) is a standard that defines an environment for the development and deployment of enterprise applications. It reduces the cost and complexity of developing multitier enterprise applications as it provides a multitier distributed application model. In other words, it is inherently distributed and therefore the various parts of an application can run on different devices.

Web applications developed using JavaServer Pages (JSP) may require some interaction with J2EE services. For example, a web-based inventory control system may need to access J2EE's directory services to gain access to a database. Or you may want to use Enterprise JavaBeans (EJB) in your application.

This article presents a brief overview of J2EE, then it shows how to: Describe J2EE services in a Web Deployment Descriptor (web.xml)

Reference J2EE services

Access and use J2EE services from JSPs

Overview of J2EE

The J2EE is a standard platform for the development and deployment of enterprise applications. The architecture of J2EE, which is component-based, makes developing enterprise applications easy because business logic is organized into reusable

components and the underlying service is provided by J2EE in the form of a container for every component type. Think of a container as the interface between the component and the low-level functionality that supports the component. Therefore, before an application client component can be executed, it must be configured as a J2EE service and deployed into its container.

J2EE promotes the development of multitier applications in which the web container hosts web components that are dedicated to handling a given application's presentation logic, and responds to requests from the client (such as the web browser). The EJB container, on the other hand, hosts application components that respond to requests from the web tier as shown in Figure 1.

Figure 1: Multitier Applications

Applications that use this architecture are implicitly scalable. This architecture decouples the accessing of data from end-user interactions, and encourages component-based code reusability. At the web tier, J2EE promotes the use of JSPs for the creation of dynamic content for Web clients.

Custom Tags and J2EE

J2EE has a lot to offer to Web application developers and the JSP custom tag developer. As you can see from Table 1 above, it has a rich set of standard APIs for sending email, accessing databases, parsing XML documents, and so on. Your Web applications can benefit greatly from these APIs. For example, you can write a JSP custom tag for sending email that can be used easily by Web content developers who are not familiar with Java. If you are not familiar with JSP custom tags, their benefits, and how to create them, please refer to Developing JSP Custom Tags.

外文资料译文

Javaserverpages概况

Javaserverpages(jsp)技术，使Web开发人员和设计师可以快速开发和易于维护，利用现有的业务系统的动态网页使信息丰富。作为在Java技术家族，JSP技术能够迅速发展，基于网络应用程序的独立平台。JSP技术隔离用户界面内容的一代，使设计改变整个版面，而不改变基本的动态内容。

开发者的益处

如果你是一个网页开发或设计师所熟悉的HTML，你可以:使用JSP技术，无须学习Java语言，你可以使用jsp技术，而不学习如何写javascriplets。虽然scriptlets不再需要产生一些动态内容，但仍支持以提供向后兼容性

扩展JSP语言：Java标签库开发商和设计师可以扩展JSP语言与“简单taghandlers”，这些都是用一种新的,更简单和清洁的标签扩展API。这促使越来越多的插件，再用标记库可用，这反过来又减少了代码需要，写出强大的Web应用。

易写和维护页面: 在JavaServerPages的标准标签库(纯)语言表达现已并入JSP 技术,并已支持升级功能。现在可以用表达语言来代替scriptlet词句。

JSP技术和Java Servlets

JSP技术使用XML式的标签，产生概括的逻辑内容页。应用逻辑可以存在于基于服务器资源(如JavaBeans组件结构) 取用这些标签的页面。

任何及所有格式化(HTML或XML)的标记直接传递回响应页面。通过把页面逻辑从它的设计陈列和支持重用的基于组件的设计中分离出来，JSP技术使得它更快，比以往更加容易地建立Web应用。

JavaServerPages的技术是一种扩展的JavaServlet技术。Servlets是具有的平台独立性的服务器端模块，能够很好的适合Web服务器架构，可以用来以最小的扩展、维护和支持一个网络服务器能力。不像其他的脚本语言，servlets涉及任何平台的具体审议或修改；按要求并下载这些应用部件，该系统的一部分也需要它们。

JSP技术和servlets一起提供了一个有吸引力的替代其他类型的动态网页脚本/编程。通过提出平台的独立性；增强性能；分离逻辑设计；易于管理；扩展进入企业；而最重要的是易用。为建设交互式Web应用，今天servlets是一种流行的选择。第三方servlet容器对于Apache服务器、MicrosoftIIS和其他服务器是一样适用的。servlet容器通常是一个网络和应用服务器的组成部分，如BEAweblogic 应用服务器、IBM的websphere、太阳JavaSystemweb服务器、SunJava系统应用服务器等等。

行业背景

JSP的规格由SunMicrosystems公司的全行业与产业界领袖企业和软件开发工具市场的产品。SUN使得jsp规格免费提供给开发社区，其目标是每一个网络服务器和应用服务器能支持JSP的接口。JSP页面共享了Java技术"写一次,到处运行"的优势。JSP技术的一个关键组成部分是Sun的在Java2平台企业版上的高扩展架构企

业应用系统。

JSP技术的Javaee5平台

Javaee5的焦点是便于开发利用Java语言说明而推出的J2se5.0。Jsp2.1通过界定说明依赖加入Jsptaghandlers和背景的听众支持这一目标的。Javaee5规格另一主要关切的问题是已调整了其webtier技术，即Javaserverpages(Jsp)、JavaServerFaces(JSF)和JavaServerPages标准标签库(JSTL)。这条路努力的结果一直是统一的表达语言(ＥＬ) ，它是语言表达定义的JSP2.0和JSF 1.1的统一体。统一的EL是主要的附加关键，调整工作有: 一个可插拔API为解决变量参照Java对象以及解决的性能来适用这些Java对象；支持延迟表达，这可能是评价一个taghandler时需要的，不像其表达式的同类，当一页需要被执行和放弃的时候立即评价；支持出现在一任务运作的左手方面的lvalue表达，当作为lvalue使用时，一架EL表达代表提到了一个数据结构，例如: 一个JavaBeans的财产，这是一些用户输入。统一的新EL是指在自己的规范文件,即随着jsp2.1规范发表。多亏了统一EL，JSTLtags,如JSTLiterationtags，现在可以用JSF组成一个直观的方式。

Javaservlet技术的概况

servlets是Java技术的选择，以扩大和加强网络服务器， servlets提供一个基于组件的平台独立的方法建立Web应用，没有CGI程式的局限性的。不像专有服务器扩展机制(如netscape服务器API或Apache模块)，servlets服务器的平台是独立的。这使得您可以服务器、平台和工具自由选择"最佳品种"的策略。Servlets 连接JavaAPIs家族，包括JDBC API连接企业数据库。Servlets还可以进入HTTP-specific calls库，并继承所有成熟的JAVA语言好处，包括可移植性、可操作性、可重用性、可维护性。为建设交互式Web应用，今天Servlets是一种流行的选择，而第三方Servlet容器可以和Apache、MicrosoftIIS等服务器兼容。Servlet 容器通常是网络和应用服务器的一个组成部分，如BEAweblogic应用服务器、IBM 的websphere、太阳JavaSystemweb服务器、SunJava系统应用服务器等等。你也许会搜索Java Server Pages(JSP)技术的最新资料。其实，JSP技术是创造支持写HTML和XML页面的Servlet技术的延伸，它使人们更容易将静态的模板数据与动态内容连接起来。即使你很喜欢写servlets，但是把调查JSP技术作为一种补充您现有的工作，也存在一些令人信服的其它理由。

JavaBeans

Javabeans技术是Java2平台标准版(J2SE)的建筑构件的。组件(JavaBeans等)是一种基于JavaBeans规范技术的可重用的软件项目，你可以通过容易的开发和组装去创造复杂的应用。

The Bean Builder

The Bean Builder是一个应用组件装配机制显示视觉结构和应用的简单组件。JavaBeans Activation Framework (JAF)

JAF能让您利用标准的服务:决定任意片数据类型、获取资讯、发现可供操作的资讯，并且通过适当的Bean实例来完成操作。Java2企业版(J2EE)是一种为开发和部署企业应用规定环境的标准。它降低了开发多层企业应用系统的成本和复杂性，因为它提供了一个多层分布式应用模型。换句话说，它可以继承性的扩展，因此通过各种申请，它也可以运行在不同的装置上。

使用Java Server Pages(JSP)进行Web应用开发，可能需要一些互动的J2EE服务。举例来说，一个网上的库存控制系统可能需要获取J2EE的目录服务获取一个数据库，或者你可以申请使用EnterpriseJavaBeans技术(EJB)。

这篇文章简要介绍了J2EE技术，它显示如何:

描述J2EE技术服务网络部署 (web.xml)

参考j2ee服务

获取和运用J2EE服务JSP

J2EE概况

J2EE的一个用于开发和部署企业应用的标准平台。基于组件的J2EE架构使得开发企业应用更加容易，因为业务逻辑是组织可重用的组件，并且基本服务是由 J2EE以容器的形式为每一个部件种类提供的。可以假想成一个组件和低层功能性组件的接口容器，因此，在一个应用客户组件能够执行前，它必须配置为J2EE的服务，并部署到其容器。

J2EE促进web容器主持网组分致力处理一种特定应用的介绍逻辑，并且反应请求从客户多层应用的发展(例如浏览器)。另一方面，EJB容器主持反应请求从web层如图1所显示的应用组分。

图1 ：多层应用

使用这建筑学的应用是可升级的。这建筑学分离访问数据从终端用户互作用，并且鼓励基于组分的代码可再用性。在web层，J2EE促进对JSPs的用途为动态内容的创作为网络客户端。

Custom Tags and J2EE

J2EE有很多为Web应用程序开发商和JSP定制标记开发商提供。您能从表1看上述，它有标准APIs充足的规定为送电子邮件，访问的数据库，解析XML文件，等等。您的Web 应用程序可能从这些APIs很大地有益于。例如，您能为送可以由网络内容开发商容易地使用不熟悉Java的电子邮件写JSP定制标记。如果您不熟悉JSP定制标记，他们的好处，和如何创造他们，参见开发的JSP定制标记。