掌握JSP核心标准标签库：JSTL Core详解

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JSTL (JavaServer Pages Standard Tag Library) 是 Java 开发中不可或缺的一部分，特别是对于那些进行Web开发的工程师而言。原版的 `CoreJSTL: Mastering the JSP™ Standard Tag Library` 是一本深入研究 JSP 核心标签库的专业技术参考书籍。该书由 Prentice Hall Professional Technical Reference (PHPTR) 出版，这是一家拥有悠久历史的出版社，自1960年代以来一直致力于计算机科学出版，目前已成为全球领先的科技书籍提供商。书中详细介绍了 JSP 的核心技术——JSTL，它在简化动态网页开发、提高代码可读性和重用性方面扮演着关键角色。JSTL 提供了一系列预定义的标签，如条件语句、循环控制、数据处理、国际化等功能，使得开发者无需频繁编写复杂的Java代码，可以直接在JSP页面上进行高效的编程。 JSP Core Tag Library 包括以下主要组件： 1. `<c:forEach>`：用于遍历集合或数组。 2. `<c:if>` 和 `<c:else>`：条件语句，判断某个表达式的真假并执行相应的代码块。 3. `<c:choose>` 和 `<c:when>`：多条件分支结构，类似于switch语句。 4. `<c:out>`：用于输出变量或字符串，可以格式化和转义输出。 5. `<c:set>` 和 `<c:param>`：设置变量值和传递参数。 6. `<c:import>`：导入其他JSP文件或EL表达式库。 7. `<fmt>`：日期和数字格式化标签，如 `<fmt:formatDate>` 和 `<fmt:parseDate>`。 8. `<c:redirect>` 和 `<c:forward>`：页面跳转和重定向操作。学习这本书不仅有助于理解JSTL的基本概念，还能提升 Web 开发者的效率，使他们能够更轻松地构建功能丰富的动态网站。书中可能还会涉及JSP页面生命周期、EL（Expression Language）表达式以及与Servlet交互的最佳实践等内容。对于想要进一步提升 JSP 技能或者准备面试的开发人员来说，这是一本非常有价值的参考资料。随着技术的发展，JSTL 在现代Web开发中依然保持着其地位，并且随着Spring MVC等框架的兴起，对JSTL的理解也变得越来越重要，因为它提供了基础的控制结构和数据处理能力，可以与各种现代框架无缝集成。因此，无论是初学者还是经验丰富的开发者，深入学习和掌握 JSTL 都是持续提升专业技能的重要途径。

Core JSTL: Mastering the JSP™ Standard Tag Library

Page15

</contact>

...

</rolodex>

The preceding XML document is a Rolodex that keeps track of a collection of contacts. For brevity, only the first

entry in the Rolodex is listed above. The code fragment listed below parses that document and creates an HTML

table that shows the data associated with each entry in the address book:

[10]

See " Parsing XML " on page 432 for more information about that code.

<c:import var='rolodex_xml' url='rolodex.xml'/>

<x:parse var='document' xml='${rolodex_xml}'/>

<table>

<x:forEach select='$document//contact'>

<table>

<tr><td>First Name:</td>

<tr><td>Email:</td>

<tr><td>Work Phone:</td>

<x:if select='phone[@type="home"]'>

<tr><td>Home Phone:</td>

</x:if>

</table><br>

</x:forEach>

</table>

The preceding code fragment uses the <x:parse> action to parse the Rolodex XML document. Subsequently, it

uses the <x:forEach>, <x:out>, and <x:if> actions to show the contacts in an HTML table; that output looks like

this:

First Name: Anna

Last Name: Keeney

Email: anna.keeney@worldlink.net

Work Phone: 716-873-9644

Home Phone: 716-834-8772

...

The JSTL Tag Library Validators

JSTL lets you eliminate almost all JSP scriptlets and expressions from your JSP code, which makes your code

more maintainable and extensible. It will take some discipline on your part, however, to keep scriptlets and

expressions out of your code; occasionally, you might have to implement a servlet or custom action to assist you in

that endeavor.

Instead of relying on discipline to keep JSP scriptlets and expressions out of your code, you can use one of the

JSTL tag library validators to enforce that restriction. That validator lets you allow or disallow the following:

• JSP declarations

• JSP expressions

• JSP scriptlets

Core JSTL: Mastering the JSP™ Standard Tag Library

Page18

<body>

<% new java.util.Date(); %>

</body>

</html>

At translation time, the preceding JSP page will throw an exception because it has a scriptlet, which violates the

first TLD declared in the page.

Now that you know what JSTL is and what it offers, let's get started by downloading and installing the necessary

software and implementing a simple Web application that uses JSTL.

1.2 Getting Started

Getting started with JSTL is easy; you need:

• The Java 2 Platform, either J2SE (Standard Edition) or J2EE (Enterprise Edition)

• A servlet container that supports the Servlet 2.3 and JSP 1.2 APIs

• JSTL

If you don't plan to use J2EE features such as Java Naming and Directory Interface (JNDI) or Enterprise

JavaBeans (EJB), you're probably better off with J2SE, which is a subset of J2EE.

You can download the J2SE, which is available for Linux, Solaris, and Windows, at

http://java.sun.com/j2se/1.4/download.html; you can download J2EE at http://java.sun.com/j2ee/sdk_1.3. For other

platforms, such as Mac OSX, check to see if a Java 2 implementation is preinstalled.

JSTL requires a servlet container that supports the Servlet 2.3 and JSP 1.2 APIs. For running the Web applications

discussed in this book, I recommend either Tomcat 4.1.3 (or later) or Resin 2.1.2 (or later). See "Tomcat" on page

26 and "Resin" on page 28, for more information about those servlet containers.

Finally, of course, you need a JSTL implementation. Some servlet containers, such as Resin, already offer their

own JSTL implementations, but as this book went to press, those implementations were immature. To test this

book's examples, I recommend you use the JSTL Reference Implementation, which is discussed in "The JSTL

Reference Implementation" on page 24.

This section shows you how to download the JSTL specification and download and install Tomcat, Resin, and the

JSTL Reference Implementation. "A Simple JSTL Web Application" on page 30 discusses a simple JSTL example

to get you started.

The JSTL Specification

You may find it useful to have the JSTL specification on hand while you use JSTL, so before we discuss

downloading servlet containers and JSTL, let's take a look at how to download the specification. If you're not

interested in the specification, you may prefer to skip ahead to one of the following destinations:

• "The JSTL Reference Implementation" on page 24

• "Downloading and Installing a Servlet Container" on page 26

• "A Simple JSTL Web Application" on page 30

You can download the JSTL specification at this URL: http://jcp.org/aboutJava/communityprocess/final/jsr052/.

The specification is a PDF file, so you will probably use Acrobat to view it, as shown in Figure 1-1.

Figure 1-1. The JSTL 1.0 Specification

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