📄 struts-bean.html
字号:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>The Struts Framework Project - Bean Tags</title>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
<meta content="Craig R. McClanahan" name="author" />
<link href="../struts.css" type="text/css" rel="stylesheet" />
</head>
<body>
<div id="heading">
<a href="http://apache.org/">
<img id="asf_logo_wide" alt="The Apache Project" src="../images/asf_logo_wide.gif" />
</a>
<a href="http://struts.apache.org/">
<img id="struts-logo" alt="Struts Framework" src="../images/struts.gif" />
</a>
</div>
<!--end heading-->
<div id="content">
<div id="menu">
<p>User Guide</p>
<ul>
<li>
<a href="index.html">Table of Contents</a>
</li>
<li>
<a href="preface.html">Preface</a>
</li>
<li>
<a href="introduction.html">Introduction</a>
</li>
<li>
<a href="building_model.html">Model Components</a>
</li>
<li>
<a href="building_view.html">View Components</a>
</li>
<li>
<a href="building_controller.html">Controller Components</a>
</li>
<li>
<a href="configuration.html">Configuration</a>
</li>
<li>
<a href="release-notes.html">Release Notes</a>
</li>
<li>
<a href="installation.html">Installation</a>
</li>
</ul>
<p>Developer Guides</p>
<ul>
<li>
<a href="dev_bean.html">Bean Tags</a>
</li>
<li>
<a href="dev_html.html">HTML Tags</a>
</li>
<li>
<a href="dev_logic.html">Logic Tags</a>
</li>
<li>
<a href="dev_nested.html">Nested Tags</a>
</li>
<li>
<a href="dev_tiles.html">Tiles Tags</a>
</li>
<li>
<a href="dev_util.html">Utilities</a>
</li>
<li>
<a href="dev_validator.html">Validator</a>
</li>
</ul>
<p>Quick Links</p>
<ul>
<li>
<a href="../index.html">Welcome</a>
</li>
<li>
<a href="index.html">User and Developer Guides *</a>
</li>
<li>
<a href="../faqs/index.html">FAQs and HowTos</a>
</li>
</ul>
</div>
<!--end menu-->
<div id="main">
<h2 id="top">Struts Bean Tags</h2>
<div class="indent">
<p>This tag library contains tags useful in accessing beans and their
properties, as well as defining new beans (based on these accesses)
that are accessible to the remainder of the page via scripting variables
and page scope attributes. Convenient mechanisms to create new beans
based on the value of request cookies, headers, and parameters are also
provided.</p>
<p>Many of the tags in this tag library will throw a
<code>JspException</code> at runtime when they are utilized incorrectly
(such as when you specify an invalid combination of tag attributes). JSP
allows you to declare an "error page" in the <code><%@ page %></code>
directive. If you wish to process the actual exception that caused the
problem, it is passed to the error page as a request attribute under key
<code>org.apache.struts.action.EXCEPTION</code>.</p>
<p>If you are viewing this page from within the Struts Documentation
Application (or online at <a href="http://struts.apache.org/">
http://struts.apache.org/</a>), you can learn more about using
these tags in the
<a href="../api/org/apache/struts/taglib/bean/package-summary.html#package_description">
Bean Tags Developer's Guide</a>.</p>
<table class="taglib-summary">
<thead>
<tr>
<th>Tag Name</th>
<th>Description</th>
</tr>
</thead>
<tr class="evenRow">
<td align="center">
<a href="#cookie">cookie</a>
</td>
<td>
Define a scripting variable based on the value(s) of the specified
request cookie.
</td>
</tr>
<tr class="oddRow">
<td align="center">
<a href="#define">define</a>
</td>
<td>
Define a scripting variable based on the value(s) of the specified
bean property.
</td>
</tr>
<tr class="evenRow">
<td align="center">
<a href="#header">header</a>
</td>
<td>
Define a scripting variable based on the value(s) of the specified
request header.
</td>
</tr>
<tr class="oddRow">
<td align="center">
<a href="#include">include</a>
</td>
<td>
Load the response from a dynamic application request and make it available
as a bean.
</td>
</tr>
<tr class="evenRow">
<td align="center">
<a href="#message">message</a>
</td>
<td>
Render an internationalized message string to the response.
</td>
</tr>
<tr class="oddRow">
<td align="center">
<a href="#page">page</a>
</td>
<td>
Expose a specified item from the page context as a bean.
</td>
</tr>
<tr class="evenRow">
<td align="center">
<a href="#parameter">parameter</a>
</td>
<td>
Define a scripting variable based on the value(s) of the specified
request parameter.
</td>
</tr>
<tr class="oddRow">
<td align="center">
<a href="#resource">resource</a>
</td>
<td>
Load a web application resource and make it available as a bean.
</td>
</tr>
<tr class="evenRow">
<td align="center">
<a href="#size">size</a>
</td>
<td>
Define a bean containing the number of elements in a Collection or Map.
</td>
</tr>
<tr class="oddRow">
<td align="center">
<a href="#struts">struts</a>
</td>
<td>
Expose a named Struts internal configuration object as a bean.
</td>
</tr>
<tr class="evenRow">
<td align="center">
<a href="#write">write</a>
</td>
<td>
Render the value of the specified bean property to the current
JspWriter.
</td>
</tr>
</table>
</div>
<h3 id="cookie">
<strong>cookie</strong> -
Define a scripting variable based on the value(s) of the specified
request cookie.
</h3>
<div class="indent">
<p>Retrieve the value of the specified request cookie (as a single
value or multiple values, depending on the <code>multiple</code> attribute),
and define the result as a page scope attribute of type <code>Cookie</code>
(if <code>multiple</code> is not specified) or <code>Cookie[]</code>
(if <code>multiple</code> is specified).</p>
<p>If no cookie with the specified name can be located, and no default
value is specified, a request time exception will be thrown.</p>
<table class="tag-attributes">
<thead>
<tr>
<th class="attribute">Attribute Name</th>
<th>Description</th>
</tr>
</thead>
<tr class="evenRow">
<td align="center">id</td>
<td>
<p>Specifies the name of the scripting variable (and associated page
scope attribute) that will be made available with the value of the
specified request cookie.</p>
[Required]
</td>
</tr>
<tr class="oddRow">
<td align="center">multiple</td>
<td>
<p>If any arbitrary value for this attribute is specified, causes all
matching cookies to be accumulated and stored into a bean of type
<code>Cookie[]</code>. If not specified, the first value for the
specified cookie will be retrieved as a value of type
<code>Cookie</code>.</p>
[RT Expr]
</td>
</tr>
<tr class="evenRow">
<td align="center">name</td>
<td>
<p>Specifies the name of the request cookie whose value, or values,
is to be retrieved.</p>
[Required]
[RT Expr]
</td>
</tr>
<tr class="oddRow">
<td align="center">value</td>
<td>
<p>The default cookie value to return if no cookie with the
specified name was included in this request.</p>
[RT Expr]
</td>
</tr>
</table>
</div>
<p>
<a href="#top">Back to top</a>
</p>
<h3 id="define">
<strong>define</strong> -
Define a scripting variable based on the value(s) of the specified
bean property.
</h3>
<div class="indent">
<p>Create a new attribute (in the scope specified by the
<code>toScope</code> property, if any), and a corresponding scripting
variable, both of which are named by the value of the <code>id</code>
attribute. The corresponding value to which this new attribute (and
scripting variable) is set are specified via use of exactly one of the
following approaches (trying to use more than one will result in a
JspException being thrown):</p>
<ul>
<li>Specify a <code>name</code> attribute (plus optional
<code>property</code> and <code>scope</code> attributes) -
The created attribute and scripting variable will be of the type of the
retrieved JavaBean property, unless it is a Java primitive type,
in which case it will be wrapped in the appropriate wrapper class
(i.e. int is wrapped by java.lang.Integer).</li>
<li>Specify a <code>value</code> attribute - The created attribute and
scripting variable will be of type <code>java.lang.String</code>,
set to the value of this attribute.</li>
<li>Specify nested body content - The created attribute and scripting
variable will be of type <code>java.lang.String</code>, set to
the value of the nested body content.</li>
</ul>
<p>If a problem occurs while retrieving the specified bean property, a
request time exception will be thrown.</p>
<p>The <code><bean:define></code> tag differs from
<code><jsp:useBean></code> in several ways, including:</p>
<ul>
<li>Unconditionally creates (or replaces) a bean under the
specified identifier.</li>
<li>Can create a bean with the value returned by a property getter
of a different bean (including properties referenced with a
nested and/or indexed property name).</li>
<li>Can create a bean whose contents is a literal string (or the result
of a runtime expression) specified by the <code>value</code>
attribute.</li>
<li>Does not support nested content (such as
<code><jsp:setProperty></code> tags) that are only executed
if a bean was actually created.</li>
</ul>
<p>
<strong>USAGE NOTE</strong> - There is a restriction in the JSP 1.1
Specification that disallows using the same value for an <code>id</code>
attribute more than once in a single JSP page. Therefore, you will not
be able to use <code><bean:define></code> for the same bean
name more than once in a single page.</p>
<p>
<strong>USAGE NOTE</strong> - If you use another tag to create the
body content (e.g. bean:write), that tag must return a non-empty String.
An empty String equates to an empty body or a null String, and a new
scripting variable cannot be defined as null. Your bean must return a
non-empty String, or the define tag must be wrapped within a logic tag
to test for an empty or null value.</p>
<p>
<strong>USAGE NOTE</strong> - You cannot use bean:define to <strong>instantiate</strong>
a DynaActionForm (type="org.apache.struts.action.DynaActionForm") with
the properties specified in the struts-config. The mechanics of creating
the dyna-properties is complex and cannot be handled by a no-argument
constructor. If you need to create an ActionForm this way, you must use
a conventional ActionForm.
</p>
<p>See the Bean Developer's Guide section on
<a href="../api/org/apache/struts/taglib/bean/package-summary.html#doc.Creation">
bean creation</a> for more information about these differences, as well
as alternative approaches to introducing beans into a JSP page.</p>
<table class="tag-attributes">
<thead>
<tr>
<th class="attribute">Attribute Name</th>
<th>Description</th>
</tr>
</thead>
<tr class="evenRow">
<td align="center">id</td>
<td>
<p>Specifies the name of the scripting variable (and associated page
scope attribute) that will be made available with the value of the
specified property.</p>
[Required]
</td>
</tr>
<tr class="oddRow">
<td align="center">name</td>
<td>
<p>Specifies the attribute name of the bean whose property is accessed
to define a new page scope attribute (if <code>property</code> is also
specified) or the attribute name of the bean that is duplicated with
the new reference created by this tag (if <code>property</code> is not
also specified). This attribute is required unless you specify
a <code>value</code> attribute or nested body content.</p>
[RT Expr]
</td>
</tr>
<tr class="evenRow">
<td align="center">property</td>
<td>
<p>Specifies the name of the property to be accessed on the bean
specified by <code>name</code>. This value may be a simple, indexed,
or nested property reference expression. If not specified, the bean
identified by <code>name</code> is given a new reference identified by
<code>id</code>.</p>
[RT Expr]
</td>
</tr>
<tr class="oddRow">
<td align="center">scope</td>
<td>
<p>Specifies the variable scope searched to retrieve the bean specified
by <code>name</code>. If not specified, the default rules applied by
<code>PageContext.findAttribute()</code> are applied.</p>
[RT Expr]
</td>
</tr>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -