JSTL Core Tags: URL Tags

Joined:
08/13/2009: Posts:
110

July 26, 2010 19:18:28 Last update: August 18, 2010 19:13:02

The tags

<c:import>

The <c:import> tag imports the contents of a URL and expose that in one of three ways:

Import contents from a URL and write it out to the page (url may be relative or absolute):
```
<c:import url="theUrl" />
```
Import contents from a URL and save it to a scoped variable string named by the var attribute. Use the scope attribute to define the scope of the exported variable.
```
<c:import url="theUrl" var="importTest" scope="session"/>
```
Import a URL and expose to a Reader object named by the varReader attribute. The scope attribute does not apply. The varReader scoped variable can only be accessed within the body of <c:import>.
```
<c:import url="theUrl" varReader="theReader"/>
```

<c:url>

The <c:url> tag constructs a URL and writes it out to the page or exports it as a scoped variable. The URL may be absolute (starting with a scheme, e.g., http://...), or relative. Relative URLs within the same servlet context are rewritten with session info, other URLs are not rewritten.

Write URL in page:
```
<c:url value="anotherPage.jsp"/>
```

Save URL to a variable in session scope:

<c:url value="anotherPage.jsp" var="aref" scope="session"/>

Contruct URL for another servlet context (but same host), save it to a variable in request scope (both url and context must start with "/" in this case):
```
<c:url value="/anotherPage.jsp" context="/anotherContext" var="aref" scope="request"/>
```

Construct URL with parameter and save it to a variable in page scope (default):

<c:url value="/anotherPage.jsp" var="aref">
    <c:param name="param1" value="value1"/>
</c:url>

<c:redirect>

The <c:redirect> sends an HTTP redirect to the client. The URL may be absolute (starting with a scheme, e.g., http://...), or relative. Relative URLs are redirected to the same servlet context, unless the context attribute is specified.

Redirect to absoute URL:

<c:redirect url="http://www.google.com"/>

Redirect to relative URL:
```
<c:redirect url="resultsPage.jsp"/>
```

Redirect to a URL in a different servlet context:

<c:redirect url="/contact.jsp" context="/support"/>

Redirect to a URL with parameter:

<c:redirect url="query.jsp">
    <c:param name="term" value="jsp tutorial"/>
</c:redirect>

<c:param>

The <c:param> tag is nested in the bodies of the above tags. Examples are given above.

Test it
Make these additions to the expanded test application:

Create a new Java class CoreURL:

package jstl.demo.handler;

import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;

import jstl.demo.DemoHandler;

public class CoreURL implements DemoHandler {
    public void handleRequest(HttpServletRequest req,
			      HttpServletResponse resp)
		throws IOException, ServletException {
	RequestDispatcher d = req.getRequestDispatcher("/coreurl.jsp");
	d.forward(req, resp);
    }
}

Create a new JSP (coreurl.jsp) under webapp:

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/xml" prefix="x"%>
<html>
<head>
<title>JSTL Core Tags: URL</title>

<style type="text/css">
body {
    font-family: sans-serif;
}

td {
    font-size: 0.9em;
    font-style: italic;
}
</style>
</head>

<body>
<h2>&lt;c:import&gt; test</h2>
<ul>
    <li>
    Write out to page: <c:import url="to_be_included.html"/>
    </li>

    <li>
    Read to String variable and write out with &lt;c:out&gt;:
    <c:import url="to_be_included.html" var="importTest" scope="session"/>
    <c:out value="${importTest}" escapeXml="false"/>
    </li>

    <li>
    Read RSS feed to Reader variable and parse with JSTL:
    <c:import url="http://slashdot.org/firehose_recent.rss" 
	      varReader="rssReader">
	<x:parse var="feed" doc="${rssReader}"/>
	<table cellspacing="0" cellpadding="4">
	<x:forEach var="story" select="$feed/*[local-name()='RDF']/*[local-name()='item']">
	    <tr><td><x:out select="*[local-name()='title']"/></td></tr>
	</x:forEach>
	</table>
    </c:import>
    </li>
</ul>

<h2>&lt;c:url&gt; test</h2>
<ul>
    <li>
	Write URL in page: <c:url value="anotherPage.jsp"/>
    </li>

    <li>
	Save URL to a variable in session scope:
	<c:url value="sessionUrl.jsp" var="aref" scope="session"/>
	<c:out value="${sessionScope.aref}"/>
    </li>

    <li>
	Construct URL for another context:
	<c:url value="/c2Page.jsp" context="/c2"/>
    </li>

    <li>
	Construct URL with parameters:
	<c:url value="/paramDemo">
	    <c:param name="param1" value="value1"/>
	</c:url>
    </li>
</ul>

<h2>&lt;c:redirect&gt; test</h2>
<c:if test="${param.redirect == 'true'}">
    <c:redirect url="${pageContext.request.requestURL}"/>
</c:if>
</body>
</html>

Add a static HTML file to_be_included.html under webapp:
```
This content is from "<i>to_be_included.html</i>".
```
Compile and package the WAR with: mvn package
Deploy the WAR to a servlet container of your choice (for example, Tomcat 6).
Test the page with this URL (Tomcat 6 running on port 8080):
http://localhost:8080/jstl-demo/demo/CoreURL
Test URL redirect with:
http://localhost:8080/jstl-demo/demo/CoreURL?redirect=true

Notice the URL change in the address bar.

You may adjust the URL if your servlet container runs on a different port or the web app is bound to a different context root.

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JSTL Core Tags: URL Tags