kooyee — Fri, 30 May 2008 14:32:00 GMT

JSTL 不能正确输出的问�?br />
�׃��Jsp2.0向后兼容的特性，当遇��C��用Jsp 1.2�Q�Servlet v2.3�Q�的�|�站时会默认的禁用JSP2.0 EL�Q�所以导致c:out不能正确输出�?br /> �Q�这里注意Jsp 1.2��用JSP2.0的EL�Q�而是��M��用JSTL 1.0 taglib去解析EL。所以��用JSP 1.2+JSTL 1.0不会出问题，而��用了JSP 1.2+JSTL 1.1��׃��D��c:out不能正确输出�Q?br />
启用EL或修改webv.xml为jsp2.0可以解决问题�?br />

启用EL�Q�在jsp��面中加�?/strong>
<%@ page isELIgnored="false"%>

page指��o的isELIgnored屬性是控制EL的��用權�?它的兩個�?true和false
如果 isELIgnored='true'表示��用EL,isELIgnored='false' 表示可以使用EL�Q?默認是false

修改webv.xml为jsp2.0

��Z��用EL改�ؓ

xml version="1.0" encoding="ISO-8859-1"?>

<web-app xmlns=" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
      http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
    version="2.4">

  <display-name>WebModule1 display-name>
web-app>

参考：
JSTL 1.0 requires JSP 1.2 (J2EE 1.3 platform). The key difference between JSTL 1.0 and JSTL 1.1 is that the expression language (EL) has moved from the JSTL specification to the JSP specification. The EL is therefore now part of the JSP 2.0 specification, and JSTL 1.1 requires JSP 2.0 (J2EE 1.4 platform).
A web application developed for JSP 1.2 has a servlet 2.3 deployment descriptor (web.xml). JSP 2.0 provides backwards compatibility for JSP 1.2 web applications by disabling by default the EL machinery (i.e. evaluation of EL expressions) when a web application has a servlet 2.3 deployment descriptor. A web application that uses JSTL 1.0 and which is deployed with a servlet 2.3 deployment descriptor therefore runs without any modification in a J2EE 1.4 environment because EL expressions are ignored by JSP 2.0, and JSTL 1.0 keeps evaluating them as was the case with JSP 1.2.
To support backwards compatibility, JSTL 1.1 introduces new URIs that must be specified to use the new capabilities offered in JSTL 1.1. Among these new capabilities is the evaluation of EL expressions being performed by the JSP 2.0 container rather than JSTL itself. The new URIs for JSTL 1.1 are as follows:

http://java.sun.com/jsp/jstl/core
http://java.sun.com/jsp/jstl/xml
http://java.sun.com/jsp/jstl/fmt
http://java.sun.com/jsp/jstl/sql

The new URIs are similar to the old JSTL 1.0 EL URIs, except that jsp/ has been added in front of jstl, stressing JSTL's dependency on the JSP specification (which now "owns" the EL). It would have been desirable to move forward with the same EL URIs in JSTL 1.1, however this would have only been possible at the cost of losing full backwards compatibility. The JSTL Expert Group felt that maintaining backwards compatibility was more important than preserving the old URIs.
The JSTL 1.0 URIs are deprecated as of JSTL 1.1. If used, they should normally appear in a web application that has a servlet 2.3 deployment descriptor to disable the JSP 2.0 EL machinery. If used with a servlet 2.4 deployment descriptor, the JSP 2.0 EL machinery must be explicitely disabled for the pages where the JSTL 1.0 tag libraries are used. Consult the JSP specification for details.

http://jcp.org/aboutJava/communityprocess/final/jsr052/JSR52-ChangeLog_1.1_Final.html

JSP EL表达�?br />

JSP EL表达式是包含在符�?#8220;${"�?}”之间。例如，${4*8}是一个EL表达式。在Java服务器技术中�Q�不再保�?#8220;${"�?}”�W�号作�ؓEL表达式的专用�W�号。执行表辑ּ��Ӟ��JSP容器可能��大括号视�ؓ循环的�v始括可��显�C�错误，或得出错误的输出�l�果。因此，有时需要��用isElgnored属性禁用EL表达式是�?br /> Servlet2.3规范未定义EL表达式，因此在JSP1.2中默认是��用EL表达式，如果在JSP��面中出现Servlet2.3EL表达式，��被忽略。Servlet2.4定义了EL表达式的模式�Q�而JSP2.0中默认启用JSP EL表达式�?br /> <% @page isELIgnored = "true|false"%>
其中�Q�page表示��面指��o�Q�isELIgnored��定是否应忽略对EL表达式进行计��?br /> 如果isELIgnored讄��为true�Q�当EL表达式在静态文本或标签属性中出现时将被忽略；如果isELIgonred讄��为false�Q�EL表达式则由JSP容器�q�行计算�?br /> 本文来源于：��克技术博�?http://www.ineeke.cn/ , 原文地址�Q�http://www.ineeke.cn/archives/233/

kooyee 2008-05-30 22:32 发表评论

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