SBC Web Hosting - JSP and Java On the Edge

Note Custom tags follow XML coding conventions. See Appendix D for an overview of XML syntax. You must code the taglib directive before coding any references to the custom tags from the tag library. Well, that s the story on coding JSP directives. Worth repeating is that JSP directives do not produce output per se; JSP directives communicate certain parameters and set certain attributes that affect the generated servlet and resultant output page. What about JSP commands that do result in output? You ll read about these commands next, starting with JSP scripting elements. JSP Scripting Elements JSP scripting elements enable you to insert code into the JSP page that results in code in the generated servlet. Scripting elements range from one-sentence variable declares to entire Java methods. I examine three categories of scripting elements: expressions, declarations, and scriptlets. JSP Expressions A JSP expression inserts data in the resultant output page. A JSP expression has the following syntax: <%= javaExpression %> The JSP translator evaluates javaExpression, converts javaExpression into a string, and places the resultant string directly in the output page. If the expression cannot be converted to a string, the runtime throws a ClassCastException. For example, the following JSP expression generates the date and time the JSP page was requested: <%= new java.util.Date() %> Or, using a page directive that allows for an unqualified reference to the Date class with the expression: <%@ page import="java.util.*" %> <@= new Date() %> JSP expressions are evaluated at the time the JSP page is requested (by entering the name of a JSP page in the location bar of a browser or clicking a hyperlink that references the JSP page), or at runtime, not at JSP translation time. The result of the evaluation being done at runtime is that variables or objects referenced in the expression have access to any information about the request. You may use the XML form of a JSP expressions as follows: Java expression
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