📄 package-summary.html
字号:
<li>parameter - the name of the request parameter to compare to <i>value</i>
<ul>
<li>example:
<pre><logic:<i>someComparisonTag</i> value="" parameter="username"><br> Error: a username must be specified<br></logic:<i>someComparisonTag</i>><br></pre>
</li>
</ul>
</li>
<li>property - the variable to be compared with <i>value</i> is the
property (of the bean specified by the name attribute) specified by
this attribute. The property reference can be simple, nested, and/or
indexed. <i>property</i> is used in conjunction with <i>name</i> to
specify a property in the bean specified by <i>name</i>. For the type
of syntax used for property, see the users guide on the Bean Tags.</li>
<li>scope - the bean scope within which to search for the bean named
by the name property, or "any scope" if not specified. Possible values
are "page", "request", "session", "application", or "any scope"
</li>
</ul>
<p><b>Substring Matching</b> (match, notMatch)</p>
<p>The substring matching tags take all the same arguments as the value
comparison tags. You compare the String specified by <i>value</i> to
any of the comparison values you give it, specified by <i>cookie</i>,
<i>header</i>, <i>parameter</i>, <i>property</i> or <i>name.</i> Note
that in the examples, <i>matchTag</i> corresponds either the <i>match
</i>or <i>notMatch</i> tag. Matching tags also have an additional <i>
location</i> attribute added:</p>
<ul>
<li>location - has two possible values, "start" and "end". If
"start", the substring is attempted to be matched at the beginning
of the String, if "end", then the substring is attempted to be matched
to the end of the String
<ul>
<li>example:
<pre><logic:<i>matchTag</i> parameter="action" value="processLogin" location="start"><br> Processing Login....<br></logic:<i>matchTag</i>><br><br>In this example, a request parameter "action" was compared to see if<br>its value started with the String "processLogin". In this case,<br><i>matchTag</i> would have to be <logic:match>.<br></pre>
</li>
</ul>
</li>
</ul>
<p><b>Presentation Location</b> (forward, redirect)</p>
<p>The <i>redirect</i> tag is resposible for sending a re-direct to the
client's browser, complete with URL-rewriting if it's supported by the
container. Its attributes are consistent with the Struts HTML <a href="../../../../../../userGuide/struts-html.html#link"><code>
link</code></a>
tag. The base URL is calculated based on which of the following attributes
you specify (you must specify exactly one of them):</p>
<ul>
<li> forward - Use the value of this attribute as the name of a global
ActionForward to be looked up, and use the context-relative URI found
there. </li>
<li>href - Use the value of this attribute unchanged. </li>
<li>page - Use the value of this attribute as a context-relative URI,
and generate a server-relative URI by including the context path. </li>
</ul>
<p>The <i>forward</i> tag is responsible for either redirecting or forwarding
to a specified global action forward. To define a global ActionForward,
see The <a href="../../../../../../userGuide/building_controller.html#config">
Action Mappings Configuration File</a>
. You can specify whether the forward re-directs or forwards when executed
in the config file. The forward tag has one attribute:</p>
<ul>
<li>name - The logical name of the ActionForward to use</li>
</ul>
<p><b>Collection Utilities</b> (iterate)</p>
<p>The <i>iterate</i> tag is responsible for executing its body content
once for every element inside of the specified Collection. There is one
required attribute:</p>
<ul>
<li>id - The name of a page scope JSP bean that will contain the current
element of the collection on each iteration</li>
</ul>
<p>The other attributes allow for more flexibility on which Collection
to iterate and how to do it:</p>
<ul>
<li>collection - a runtime expression that evaluates to a Collection
to be iterated
<ul>
<li>example:
<pre><%<br> java.util.Vector vector = new java.util.Vector();<br> vector.add(new Integer(12));<br> vector.add(new Integer(5));<br> %><br></pre>
</li>
</ul>
</li>
</ul>
<blockquote>
<blockquote>
<pre><logic:iterate id="myCollectionElement" collection="<%= vector %>"><br><i> Do something with myCollectionElement</i>
</logic:iterate>
</pre>
</blockquote>
</blockquote>
<ul>
<li>length - The maximum number of entries (from the underlying collection)
to be iterated through on this page. This can be either an integer
that directly expresses the desired value, or the name of a JSP bean
(in any scope) of type java.lang.Integer that defines the desired value.
If not present, there will be no limit on the number of iterations
performed</li>
<li>name - The name of the JSP bean containing the collection to be
iterated (if property is not specified), or the JSP bean whose property
getter returns the collection to be iterated (if property is specified).
<ul>
<li>example:
<pre><%<br>
java.util.ArrayList list = new java.util.ArrayList();
list.add("First");
list.add("Second");
list.add("Third");
list.add("Fourth");
list.add("Fifth");
pageContext.setAttribute("list", list, PageContext.PAGE_SCOPE);
%>
<logic:iterate id="myCollectionElement" name="list">
<i>Do something with myCollectionElement</i>
</logic:iterate></pre>
</li>
</ul>
</li>
<li>offset - The zero-relative index of the starting point at which
entries from the underlying collection will be iterated through. This
can be either an integer that directly expresses the desired value,
or the name of a JSP bean (in any scope) of type java.lang.Integer
that defines the desired value. If not present, zero is assumed (meaning
that the collection will be iterated from the beginning. </li>
<li>property - Name of the property, of the JSP bean specified by name,
whose getter returns the collection to be iterated. See the user's
guide for the bean tag library for the syntax of the property attribute</li>
<li>scope - The bean scope within which to search for the bean named
by the name property, or "any scope" if not specified. Possible values
are "page", "request", "session", "application", or "any scope"
</li>
<li>type - Fully qualified Java class name of the element to be exposed
through the JSP bean named from the id attribute. If not present, no
type conversions will be performed. NOTE: The actual elements of the
collection must be assignment-compatible with this class, or a request
time ClassCastException will occur.
<ul>
<li>example:
<pre><% java.util.ArrayList list = new java.util.ArrayList();<br>list.add("First");<br>list.add("Second");<br>list.add("Third");<br>list.add("Fourth");<br>list.add("Fifth");<br> pageContext.setAttribute("list", list, PageContext.PAGE_SCOPE);<br> %><br><br><logic:iterate id="myCollectionElement" name="list" type="java.lang.String"><br> <i>Do something with myCollectionElement</i>
</logic:iterate></pre>
</li>
</ul>
</li>
</ul>
</blockquote>
<h3>Logic Examples<a name="doc.Examples"></a></h3>
<blockquote>
<p><b>Value Comparisons</b></p>
<blockquote>
<p><u></u><u></u><u>Logic Equivalence Tags (equal, notEqual, greaterEqual,
lessEqual, lessThan, greaterThan)</u></p>
<blockquote>
<p>You can compare these tags to the "==", "!=" ,">=",
"<=", "<", and ">"logic operators in most languages.
Their usage is fairly straightforward for numbers. For an example,
we'll create a small "Guess That Number" game that uses request parameters
from a form input to play. The number will be hardcoded as "7", because
this is just an example. Note that this is actually putting application
logic inside of jsp pages, and isn't the recommended development
method for Struts. It's just an easy way to show how these tags are
used:</p>
<p>The first step is to develop the form that will call on the
processing jsp page. This form will use the "GET" method so that
you can see the request parameter in the URL. The POST method can
also be used with no problem or changes.</p>
<p>[numberGuess.jsp]</p>
<pre><form action="numberProcess.jsp" method="GET"><br>Please Enter a Number From 1-10: <input type="text" name="number" /><br /><br> <center><br> <input type="submit" name="Guess Number" /><br> </center><br></form><br></pre>
The next step is to create the processing page. It uses the struts-logic
taglib. For information on how to set this tag library up in your application
to use, see <a href="../../../../../../userGuide/configuration.html#dd_config">
The Web Application Deployment Descriptor</a>
<p>[numberProcess.jsp]</p>
<pre><%@ page language="java" %><br><%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %><br></pre>
<pre><!-- Is the number guess right? --><br><logic:equal parameter="number" value="7"><br> You guessed right! You win a high speed blender!<br></logic:equal><br></pre>
<pre><!-- If the number guessed was wrong --><br><logic:notEqual parameter="number" value="7"><br> <!-- Less Than --><br> <logic:lessThan parameter="number" value="7"><br> A little higher...<br> </logic:lessThan><br> <!-- Greater Than --><br> <logic:greaterThan parameter="number" value="7"><br> A little lower...<br> </logic:greaterThan><br></logic:notEqual><br></pre>
<p>Basically, the numberProcess.jsp page uses the equal tag to
check if the guess is 7, and if so, prints out a congratulatory message.
If the number isn't equal, specified by the use of the <logic:notEqual>
tag, it uses the greaterThan and lessThan tags to check if the number
is higher or lower than 7, and prints out a hint. As said before,
this is a horribly designed small application, with no validity checks
on the number input, but shows the basic usage of the logic equal
tags</p>
<p>For String comparisons, the equal tags use the java.lang.String.compareTo()
method. See the javadocs on the compareTo() method for more information,
located <a href="http://www.javasoft.com/products/jdk/1.2/docs/api/java/lang/String.html#compareTo%28java.lang.Object%29">
here</a>
.</p>
</blockquote>
<p><u>Match and Present Tags (match, notMatch, present, notPresent)</u></p>
<blockquote>
<p>You use the match tags in conjunction with the present tags
in order to do substring matches. For an example using this we'll
use headers, specifically the "Referer" header. The HTTP referer
header gives the URL of the document that refers to the requested
URL. We'll use this to check if the user is coming from a link specified
by a <a href="http://www.google.com">Google</a>
search, and offer a personalized greeting, frightening users that
find our site through the search engine with our amazing intimate
knowledge of their browsing habits:</p>
<p>[sneaky.jsp]</p>
<pre><%@ page language="java" %><br><%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %><br><br><br><!-- Check to see if the "Referer" header is present --><br><logic:present header="Referer"><br> <logic:match header="Referer" value="google.com"><br> I see you found our site through Google... interesting.<br> </logic:match><br> <logic:notMatch header="Referer" value="google.com"><br> Welcome to the site, we're secretly logging what site you came from,<br> because we're shady...<br> </logic:notMatch><br></logic:present><br><br><!-- If the header is not present --><br><logic:notPresent header="Referer"><br> Hi, welcome to our site. Please fill out our<br> <a href="nonExistantForm.jsp">Form</a> and<br> tell us where you're coming from.<br></logic:notPresent></pre>
<p>Note: Another interesting usage of these tags and headers
would be to use the "User-Agent" header to display browser-specific
javascript.</p>
</blockquote>
</blockquote>
<p><b>Collection Utilities (iterate)</b></p>
<blockquote>
<p>For an example of using the <logic:iterate> tag,
we'll use one of the previous examples given, in it's entirety. This
example uses the <bean:write> tag from the Bean Tag Library,
see the User's Guide on the bean tag library for more information on
it's usage:</p>
<p>[iterate.jsp]</p>
<pre><%@ page language="java" %><br><%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %><br><%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %><br></pre>
<pre><%<br>java.util.ArrayList list = new java.util.ArrayList();<br> list.add("First");<br> list.add("Second");<br> list.add("Third");<br> list.add("Fourth");<br> list.add("Fifth");<br> pageContext.setAttribute("list", list, PageContext.PAGE_SCOPE);<br>%><br><br><logic:iterate id="myCollectionElement" name="list"><br> Element Value: <bean:write name="myCollectionElement" /><br /><br></logic:iterate></pre>
</blockquote>
</blockquote>
<P>
<HR>
<!-- ========== START OF NAVBAR ========== -->
<A NAME="navbar_bottom"><!-- --></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0">
<TR>
<TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1">
<A NAME="navbar_bottom_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3">
<TR ALIGN="center" VALIGN="top">
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD>
<TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Package</B></FONT> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <FONT CLASS="NavBarFont1">Class</FONT> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-use.html"><FONT CLASS="NavBarFont1"><B>Use</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../../index-all.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD>
</TR>
</TABLE>
</TD>
<TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM>
</EM>
</TD>
</TR>
<TR>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../../../org/apache/struts/taglib/html/package-summary.html"><B>PREV PACKAGE</B></A>
<A HREF="../../../../../org/apache/struts/taglib/nested/package-summary.html"><B>NEXT PACKAGE</B></A></FONT></TD>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../../../index.html" TARGET="_top"><B>FRAMES</B></A>
<A HREF="package-summary.html" TARGET="_top"><B>NO FRAMES</B></A></FONT></TD>
</TR>
</TABLE>
<!-- =========== END OF NAVBAR =========== -->
<HR>
Copyright ⌨️ 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 + -