Recipe 12.4 Creating a New Window with JavaScript in a JSP

Problem

You want to use JavaScript in a JSP to create a new browser window.

Solution

Use the c:import JSTL tag to import the JavaScript code into the JSP. Then use the initParam JSTL implicit object to dynamically provide the URL for a JavaScript-generated window.

Discussion

The JSP in Example 12-5 (windowJ.jsp) uses the JSTL's c:import core tag to import the JavaScript function definition for creating a new window. The JSP then calls the JavaScript function (CreateWindow) in the onClick event handler for a web page button. The CreateWindow function loads the URL specified in its parameter into the new browser window. Example 12-5 uses the c:out core tag and EL syntax to dynamically acquire the URL for the JavaScript window from a context parameter. The c:out tag looks like this:

<c:out value=
"${pageContext.request.contextPath}${initParam[\"jsp-url\"]}"/>

The value attribute specifies two EL expressions. The first one provides the JSP's context path, while the second gives the value of the context-param element jsp-url. The full URL specified by these concatenated EL expressions is /home/cookieReader.jsp.

Example 12-5. Using the JSTL to import JavaScript into a JSP

<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>
<html>
<head>

<c:import url="/WEB-INF/javascript/functions.js" />

<title>Help Page</title></head><body>
<h2>Cookie Info</h2>

<form action ="" onSubmit=" return false">
<table border="0"><tr><td valign="top">
Click on the button to get more info on cookies: </td>  
<td valign="top">

<input type="button" name="button1" value=
    "More Info" onClick=
"CreateWindow('<c:out value=
    "${pageContext.request.contextPath}${initParam[\"jsp-url\"]}"/>')">

</td></tr>
</table></form>
</body></html>

This JSP uses the following context-param element in web.xml:

<context-param>
    <param-name>jsp-url</param-name>
    <param-value>/cookieReader.jsp</param-value>
</context-param>

The EL implicit object initParam evaluates to a java.util.Map containing the names and values of any context-param elements configured for the web application. An implicit object is a variable that the JSTL automatically makes available to your JSP code.

Example 12-5 uses the EL syntax initParam[\"jsp-url\"], as opposed to initParam.jsp-url, in order to return the intended value in Tomcat 5 (alpha version as of this writing). The code's purpose is to escape the hyphen character (-) in "jsp-url."

Recipe 12.4 Creating a New Window with JavaScript in a JSP

Problem

Solution

Discussion

Example 12-5. Using the JSTL to import JavaScript into a JSP

See Also