Java Servlet & JSP Cookbook

2017-07-07 02:10:07

Problem

You want to create a JSP document in an XML editor's tool.

Solution

Open up your XML editor of choice and create the JSP using only XML elements.

Discussion

A JSP document is a namespace-aware, well- formed XML file that contains JSP standard actions (such as jsp:include and jsp:useBean ), custom actions (such as JSTL custom tags), and the XML equivalents of JSP directives. Table 5-1 specifies the XML equivalents for common JSP directives. Write the JSP document in an XML editor, preferably one where you can check its well- formedness . The JSP document has to be a well-formed XML document to be eligible for placement into a JSP container and execution.

Table 5-1. XML equivalents for JSP directives

Directive	Example	JSP document equivalent
`<page>`	<%@ page import="java.util.Date" %>	<jsp:directive.page import="java.util.Date" />
`<include>`	<%@ include file="footer.html" %>	<jsp:directive.include file="footer.html" />
`<taglib>`	<%@ taglib uri="WEB-INF/tlds/xml_gen.tld" prefix="t" %>	<jsp:root jsp:id="0" xmlns:jsp="http://java.sun.com/JSP/Page" version="2.0" xmlns:t="urn:jsptld:/WEB-INF/tlds/xml_gen.tld">

In JSP 1.2, the only way to identify a JSP page as XML is by having a jsp:root element as the root. However, JSP 2.0 offers several new options ”the JSP 2.0 specification states that a JSP document can also be distinguished from a JSP in non-XML syntax by a jsp-property- group element in the deployment descriptor, a .jspx file extension, or a jsp:root root element.

This recipe shows a simple JSP page and its XML equivalent, then repeats the comparison with the addition of a custom tag and a runtime expression for a JSP element attribute. Example 5-9 is a simple file in JSP page syntax showing the web server's local time.

Example 5-9. A simple JSP page-syntax file

<%@page contentType="text/html"%> <%@page import="java.util.Date"%> <html> <head><title>Welcome to the Web</title></head> <body> <h2>Welcome to the Web</h2> The server's local time is <%=new Date( ) %>. </body> </html>

This JSP has two page directives and a JSP expression that displays a date and time string on the browser page. Figure 5-1 shows the execution of this page in a browser.

Figure 5-1. Simple JSP before XML conversion

This page can be converted into a JSP document by cutting and pasting the code into an XML editor and replacing non-XML constructs with XML elements. Example 5-10 is the JSP document equivalent of Example 5-9.

Example 5-10. A simple JSP document as well-formed XML

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.0"> <jsp:directive.page contentType="text/html"/> <jsp:directive.page import="java.util.Date"/> <html> <head><title>Welcome to the Web</title></head> <body> <h2>Welcome to the Web</h2> The server's local time is <jsp:expression>new Date( )</jsp:expression>. </body> </html> </jsp:root>

Example 5-10 has jsp:directive.page elements instead of traditional JSP directives, which are not valid XML elements because of the <%@ syntax. Anything in a JSP page that uses <% -style delimiters cannot be used to distinguish JSP elements, because then the JSP document will not pass an XML well-formedness test.

Example 5-11 is a more complex JSP page with a taglib directive that specifies the core tag library from JSTL 1.0; the page also uses Expression Language (EL) code. Further, the page has a jsp:useBean element that sets a java.util.Date variable dateString to page scope.

Example 5-11. A JSP page presenting a complex XML conversion

<%@page contentType="text/html"%> <%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %> <html> <head><title>Welcome to the Web</title></head> <body> <h2>Welcome to the Web</h2> Hello, <c:out value="${param.firstName} ${param.lastName}"/><br><br> <jsp:useBean id="dateString" class="java.util.Date"/> The time is <c:out value="${dateString}" />.<br><br> The value of 10 + 24 + 35 = <c:out value="${10 + 24 + 35}" /> </body> </html>

Example 5-12 is the same JSP page converted to a JSP document.

Example 5-12. Referring to tag libraries ( taglibs ) in a JSP document

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" xmlns:c="http://java.sun.com/jstl/core" version="2.0"> <jsp:directive.page contentType="text/html"/> <html> <head><title>Welcome to the Web</title></head> <body> <h2>Welcome to the Web</h2> <jsp:text>Hello </jsp:text> <c:out value="${param.firstName} ${param.lastName}"/><br></br><br></br> <jsp:useBean id="dateString" class="java.util.Date"/> <jsp:text>The time is </jsp:text><c:out value="${dateString}" />. <br></br><br></br> <jsp:text>The value of 10 + 24 + 35 = </jsp:text> <c:out value="${10 + 24 + 35}" /> </body> </html> </jsp:root>

In a JSP document, any tag libraries can be included as namespace attributes, such as in the jsp:root element, as shown here:

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" xmlns:c="http://java.sun.com/jstl/core" version="2.0">

The jsp:text element can be used to contain any template data in the JSP document. You can use the JSP standard actions such as jsp:useBean and custom tags like c:out with the same syntax used in a JSP page.

Figure 5-2 shows the browser output of the JSP document in Example 5-12. This page was requested by using this URL: http://localhost:8080/home/example_xml2.jsp?firstName=Bruce&lastName=Perry .

Figure 5-2. Output from Example 5-11

Here is what the HTML source code looks like, if you chose "View Source" from the browser menu (with some carriage returns added for readability):

<html><head><title>Welcome to the Web</title></head> <body> <h2>Welcome to the Web</h2> Hello Bruce Perry<br/><br/> The time is Mon Feb 10 16:20:05 EST 2003.<br/><br/> The value of 10 + 24 + 35 = 69 </body></html>