25-Jul-11
JSPJava Server PagesReference:
http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/Servlet-Tutorial-JSP.htmlA
Hello World servlet(from the Tomcat installation
documentation)public class HelloServlet extends HttpServlet {public
void doGet(HttpServletRequest request,HttpServletResponse
response)throws ServletException, IOException
{response.setContentType("text/html");PrintWriter out =
response.getWriter();String docType ="\n";out.println(docType +"\n"
+"Hello\n" +"\n" +"Hello World\n" +"");}}This is mostly Java with a
little HTML mixed inServletsThe purpose of a servlet is to create a
Web page in response to a client requestServlets are written in
Java, with a little HTML mixed inThe HTML is enclosed in
out.println( ) statementsJSP (Java Server Pages) is an alternate
way of creating servletsJSP is written as ordinary HTML, with a
little Java mixed inThe Java is enclosed in special tags, such as
The HTML is known as the template textJSP files must have the
extension .jspJSP is translated into a Java servlet, which is then
compiledServlets are run in the usual wayThe browser or other
client sees only the resultant HTML, as usualTomcat knows how to
handle servlets and JSP pagesJSP scripting elementsThere is more
than one type of JSP tag, depending on what you want done with the
Java
The expression is evaluated and the result is inserted into the
HTML page
The code is inserted into the servlet's service methodThis
construction is called a scriptlet
The declarations are inserted into the servlet class, not into a
method
Example JSP
Hello! The time is now
Notes:The tag is used, because we are computing a value and
inserting it into the HTMLThe fully qualified name (java.util.Date)
is used, instead of the short name (Date), because we havent yet
talked about how to do import declarations
VariablesYou can declare your own variables, as usualJSP
provides several predefined variablesrequest : The
HttpServletRequest parameterresponse : The HttpServletResponse
parametersession : The HttpSession associated with the request, or
null if there is noneout : A JspWriter (like a PrintWriter) used to
send output to the clientExample:Your hostname:
ScriptletsScriptlets are enclosed in tagsScriptlets do not
produce a value that is inserted directly into the HTML (as is done
with )Scriptlets are Java code that may write into the
HTMLExample:
Scriptlets are inserted into the servlet exactly as written, and
are not compiled until the entire servlet is compiledExample:
Have a nice day!
Have a lousy day!
DeclarationsUse for declarations to be added to your servlet
class, not to any particular methodCaution: Servlets are
multithreaded, so nonlocal variables must be handled with extreme
careIf declared with , variables are local and OKData can also
safely be put in the request or session objectsExample:
Accesses to page since server reboot:
You can use to declare methods as easily as to declare
variablesDirectivesDirectives affect the servlet class itselfA
directive has the form:
or
The most useful directive is page, which lets you import
packagesExample: The include directiveThe include directive inserts
another file into the file being parsedThe included file is treated
as just more JSP, hence it can include static HTML, scripting
elements, actions, and directivesSyntax: The URL is treated as
relative to the JSP pageIf the URL begins with a slash, it is
treated as relative to the home directory of the Web serverThe
include directive is especially useful for inserting things like
navigation barsActionsActions are XML-syntax tags used to control
the servlet engine
Inserts the indicated relative URL at execution time (not at
compile time, like the include directive does)This is great for
rapidly changing data
Jump to the (static) URL or the (dynamically computed)
JavaExpression resulting in a URL
JSP in XMLJSP can be embedded in XML as well as in HTMLDue to
XMLs syntax rules, the tags must be different (but they do the same
things)HTML: XML: expressionHTML: XML: codeHTML: XML:
declarationsHTML: XML: The End
