Java Server Pages

Java Server Pages CS-422

What are JSPs • A logical evolution of java servlets • most servlets dynamically create HTML and integrate it with some computational and database output • Servlets on their own had some pretty stiff competition form PHP, ASP and ColdFusion • these technologies for the most part (especially ColdFusion) don’t need a programmer; ASP and PHP definitely have a programming language in their background but scripting in VBScript or PHP is still easier than Java • some one at Sun recognized that a servlet was just some Java with HTML embedded in it, and thought: why not embed some Java in regular HTML; then create a class that will scan through it and make the source code for a servlet, then compile it and deploy it • The Java Server Page is born

An Example...  <html xmlns = "http://www.w3.org/1999/xhtml">  <head> <title>Processing "get" requests with data</title> </head>  <body> <% // begin scriptlet String name = request.getParameter( "firstName" ); if ( name != null ) { %> <%-- end scriptlet to insert fixed template data --%> <h1> Hello <%= name %>, <br /> Welcome to JavaServer Pages! </h1> <% // continue scriptlet } // end if else { %> <%-- end scriptlet to insert fixed template data --%> <form action = "welcome.jsp" method = "get"> <p> Type your first name and press Submit</p> <p><input type = "text" name = "firstName" /> <input type = "submit" value = "Submit" /> </p> </form> <% // continue scriptlet } // end else %> <%-- end scriptlet --%> </body> </html>

The rendered screen(s)... After entering Dick...

Embedding Java in HTML • Embedding Java in HTML is pretty simple; the lead is taken from PHP and ASP; we’ll make a special escape character “<%”, “<%=“ and “%>” • the tag pair <% …%> are used for defining scriptlets; a sequences of Java statements • scriptlets are used to glue the parts of your jsp together (see prev. example) • the tag pair <%=…%> is used for Java expression evaluation • ex <%= new java.util.Date( ) %> will be replaced with the current Date/Time

JSP Directives • page • taglib • include

page directive • Language – “scriptingLanguage” • Extends – “classname” • Import – “importList” – java.lang.*, javax.servlet.*, javax.servlet.jsp.*, and javax.servlet.http.* are imported implicitily • Session “true|false” • Buffer – “none|sizekb” • autoFlush- “true|false” • isThreadSafe – “true|false” • Info – “info_text” • errorPage – “error_URL” • isErrorPage – “true|false” • contentType – “contentInfo” • pageEncoding – “pageEncodingInfo”

taglib directive • Import a taglib into the page • Associate taglib with a URI • Map the URI to,a prefix for use within the page • <%@ taglib uri=“taglib URI” prefix=“prefix” %>

include directive • Allows the inclusion of another file into the defining page • Happens at translation time. • <%@ include file=“URL” %>

JSP Actions (Tags) • JSP provides a set of standard actions to help you with commonly done tasks: • <jsp:include> • <jsp:forward> • <jsp:plugin> • <jsp:param> • <jsp:useBean> • <jsp:setProperty> • <jsp:getProperty>

<jsp:include> • Attributes: • page - specifies the relative URI path to the resource to include • flush - must be “true” ; specifies whether the buffer should be flushed after the include is performed • <%jsp:include file=“myfile.html” flush=true> • use this action to include dynamic content; it will be included each time it is included • there is also an include directive • <%@ include file = relative URI> • use this for including static content, is included only once

<jsp:forward> • Allows you to forward processing to another JSP, as soon as processing is forwarded the processing of the curreent JSP is terminated • can be used in conjunction with <jsp:param> to forward parameter information to the forwarded JSP <jsp:forward page=“nextjsp.jsp”> <jsp:param name = date value=“<%=java.util.Date() %>” /> </jsp:forward>

<jsp:plugin> • Adds an applet or JavaBean to a Web page in the form of a browser=specific object or embed XHTML element. It also allows the client to download and install the java Plug-in if it is not already present. • Attributes: • type - bean or applet • code - Class that represents the component • codebase- location of the class specified in the code attribute and the archives specified in the archives attribute • align - Alignment od the component (left,right,center) • archive - space separated list of archives (JARS) containing resources • height - component height in pixels • hspace - number of pixels to right and left of component • jreversion - version of the JRE required • name - name of component • vspace - number of pixels above and below the component • title - Text describing the component • width - component width in pixels or percent • nspluginurl - location of plugin for Netscape Navigator • iepluginurl - location of plugin for Internet Explorer

<jsp:useBean> • Enables a JSP to manipulate or use a JavaBean. The action creates or locates an existing object for use in the JSP. • Attributes: • id - the name used to manipulate the Java object (case sensitive) • scope - page, request,session,or application (default is page) • class - fully qualified class name of the Java object • beanName - The name that can be used with method instantiate of class java.beans.Beab to load a JavaBean into memory. • Type - type of JavaBean, can be same as class attribute , a superclass of that type or an interface implemented by that type

<jsp:setProperty> • Used to set Bean property values • Attributes: • name - Id of the Bean for which a property is to be set • property - name of the property to set • param - specify which request parameter is to be used • value - the value to assign to a Bean proberty

<jsp:getProperty> • retrieve the value of a Bean property • attributes: • name - the name of the Bean • property - the name of the property to retrieve

Java Server Pages