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Java Server Pages

Learn about JSP, a document-centric specification similar to HTML with embedded Java code, directives, & actions. Explore JSP components like tags, comments, and scripting elements. JSP Directives provide instructions for the JSP container, while page directives define attributes like language and content type. Declarations and scriptlets allow for variable creation and code insertion. Discover how to include static content and execute code using JSP expressions. JavaServer Pages also offer implicit objects for accessing servlet data.

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Java Server Pages

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  1. Java Server Pages JSP JavaServer Pages

  2. Topics • JSP Overview • JSP and Java Beans • Servlet Integration • JSP Scripting • Custom Tags • JSP and WARs/EARs JavaServer Pages

  3. JSP Overview • Document-centric specification • similar to HTML • markup code embedded in the document • directives • actions • scripts • Java is the currently supported scripting language • Complementary to servlets JavaServer Pages

  4. JSP Example <HTML> <HEAD><TITLE>JSP Example</TITLE> <%@ page import="java.util.Date" %> </HEAD> <%-- Embed Date in generated output --%> <BODY> The Date is: <%= new Date() %> </BODY> </HTML> JavaServer Pages

  5. JSP Components • JSP Tags • Comments • Scripting elements • Actions • Directives JavaServer Pages

  6. JSP Comments • JSP comments are stripped out and do not appear in the generated HTML page <%-- This is a JSP comment --%> • HTML comments are supported and do appear in the generated HTML page <!-- This is an HTML comment --> JavaServer Pages

  7. JSP Directives • Instructions for JSP Container • Processed when JSP page is converted to a servlet • Directives do not cause information to be written to JSPs output • Shorthand Form <%@ page import=“javax.naming.*” %> • XML Form <jsp:directive.page import=“javax.naming.*” /> JavaServer Pages

  8. JSP Page Directives • Page directive attributes • info - defines string returned from Servlet.getServletInfo() • language - only required language is java • contentType - defaults to “text/html;charset=ISO-8859-1” <jsp:directive.page contentType=“text/xml”/> • extends - specifies the base class of the generated servlet • generally not a good idea, limits the container implementation options • import - specifies classes to import for scriptlets/beans <jsp:directive.page import=“package.Class”/> JavaServer Pages

  9. JSP Page Directives (cont.) • Page directive attributes (Cont) • session - defines implicit HttpSession session variable <jsp:directive.page session=“true”/> • buffer - specifies size of output buffer • autoFlush - flushes (true) buffer when full;throws (false) exception • isThreadSafe - dispatches requests in single thread (false) or multiple threads (true). Default is true. • isErrorPage - defines implicit java.lang.Throwable exception variable <jsp:directive.page errorPage=“true”/> • errorPage - specifies JSP to invoke on uncaught exceptions • <jsp:directive.page errorPage=“/ErrorPage.jsp”/> JavaServer Pages

  10. JSP Include Directives • Static includes done at deployment <@ include file=“fileRelativeURL” %> <jsp:directive.include file=“fileRelativeURL” /> • Same as #include is C/C++ • Imagine a page: • <jsp:directive.include file=“Header.jsp” /> • < jsp:directive.include file=“Body.jsp” /> • < jsp:directive.include file=“Footer.jsp” /> • Another form may be done at runtime<jsp:include page=“pageRelativeURL”/> JavaServer Pages

  11. JSP Declarations • Create variables (or methods) for later use in expressions or scriptlets <%! String choice; %> <jsp:declaration> String choice; </jsp:declaraion> • Code is inserted in generated servlet outside of service() method. • Object-level scope • Example <jsp:declaration> int i=0; void print() { System.out.println(i++); } <jsp:declaration> <jsp:scriptlet>print();<jsp:scriptlet> JavaServer Pages

  12. Scriptlets • Code to be inserted directly in the generated servlet and executed when page is requested • i.e. inserted in service method <% choice = request.getParameter(“Product”); %> <jsp:scriptlet> choice=request.getParameter(“Product”); </jsp:scriptlet> • Default scripting language is Java so all conditional statements, method invocations, etc. are supported JavaServer Pages

  13. Expressions • Insert results from code execution directly onto the JSP Page <P> The Date is: <%= new Date() %> </P> <P> The Date is: <jsp:expression>new Date()</jsp:expression> </P> • Automatically converts toString() and writes result JavaServer Pages

  14. Implicit Objects • page • Page’s servlet instance • config • ServletConfig (configuration data) • request • HttpServletRequest • response • HttpServletResponse JavaServer Pages

  15. Implicit Objects (Cont) • out • Output Stream for content (JspWriter) • session • HttpSession • application • ServletContext • pageContext • Context Data for page execution (PageContext) • exception • Available on error pages (java.lang.Throwable) JavaServer Pages

  16. Implicit Object Example <HTML> <BODY> <% String visitor=request.getParameter(“name”); if( visitor==null) visitor=“Unknown”; %> Hello, <%= visitor %> </BODY> </HTML> • http://localhost:7001/jsp/implicit.jsp?name=Dan • Remember: Keep URLs shorter than 255 characters JavaServer Pages

  17. JSP-Specific Tags • jsp:forward • Switch to another URL • jsp:include • Embed the contents of another URL in this page • jsp:useBean, jsp:setProperty, jsp:getProperty • Embed and use JavaBeans in a JSP Page • jsp:plugin • downloads Java plugin to client JavaServer Pages

  18. Risks • Embedding code in the HTML page is convenient, but …. • We are mixing business logic with presentation • Use JSP for simple coding e.g. Date • Defer business logic to Beans and or Servlets JavaServer Pages

  19. JSP and Java Beans JavaServer Pages

  20. What is a Bean? • Java class that follows a set of implementation and naming guidelines • Typically named xxxBean • Public no argument constructor • Setters/Getters for attributes • Indexed properties • BeanInfo interface • Should implement java.io.Serializable • Event model, bound and constrained properties JavaServer Pages

  21. HelloBean packages corej2ee.examples.web.usebean; public class HelloBean implements java.io.Serializable { String name; public HelloBean() { name=“Anonymous”; } public String getName() { return name; } public void setName(String argName) { name=argName; } } JavaServer Pages

  22. usebean.html <html> <head><title>Test of jsp use bean></title></head> <body> <h1>Enter Name</h1> <form action="usebean.jsp" method="POST"> <table border="0" width="30%" cellspacing="3" cellpadding="2"> <tr><td><b>User Name</b></td> <td><input type="text" size="20" name="name"></td></tr> <tr><td><p><input type="submit" value="Login"></td></tr> </table> </form> </body> </html> JavaServer Pages

  23. Using Java Beans in JSP <jsp:useBean id="hellobean" class="corej2ee.examples.web.usebean.HelloBean"/> <jsp:setProperty name=“hellobean” property="name" param="name"/> <HTML> Hello, <jsp:getProperty name="hellobean" property="name"/> <BODY> </BODY> </HTML> JavaServer Pages

  24. Setting Bean Attributes • jsp:setProperty tag • Can initialize bean properties from HttpRequest <jsp:setProperty name=“hello” property=“name” param=“name”/> • Param attribute (from form) is the equivalent of: request.getParameter(“name”); • Property attribute (from JavaBean) is equivalent of: hello.setName(…); • Shortcut to set all parameters in bean that match request parameter names <jsp:setProperty name=“hello” property=“*”/> • Use value attribute to set the property to a specific value • property=“name” value=“hard-coded-value” JavaServer Pages

  25. Bean Scope • Bean lifetime defaults to the execution of the page that contains the useBean tag • scope= • “page” - defined in jsp.PageContext • “request” - defined in Servlet.service()’s request object • (jsp:forward, jsp:include) • “session” - defined in user’s session object • “application” - defined in Servlet’s Context • Interesting servlet/jsp communication mechanism JavaServer Pages

  26. Benefits and Limitations • Benefits • Separates business logic from HTML content • Easier maintenance • Component Re-usability • Can be configured with commercial tools • Limitations • Java Bean event model not supported JavaServer Pages

  27. JSP Summary • Allows HTML authors to be HTML authors and not Java programmers • While Java code can be embedded in the .jsp page this should be kept to a minimum • Use JavaBeans for model data and tags as the interface between the html page and the model • Avoid HTML output from Beans • Custom Tags are useful for generating HTML JavaServer Pages

  28. JSP Custom Tags JavaServer Pages

  29. JSP Tags Overview • Capability to define your own jsp tags in a portable manner • Required components • Tag Handler class • Implements tag behavior • Tag Library Descriptor File • Define class to server and associate it with an XML tag name • XML document JavaServer Pages

  30. Tag Handler • Must implement the javax.servlet.jsp.tagext.Tag interface • doStartTag() and doEndTag() are key methods • Frequently extend TagSupport JavaServer Pages

  31. JavaServer Pages

  32. package corej2ee.examples.web.tag; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; import java.io.*; import javax.servlet.*; /** A tag that includes the body content only if * the "debug" request parameter is set. * <P> * Taken from Core Servlets and JavaServer Pages * from Prentice Hall and Sun Microsystems Press, * http://www.coreservlets.com/. * &copy; 2000 Marty Hall; may be freely used or adapted. */ public class DebugTag extends TagSupport { public int doStartTag() { ServletRequest request = pageContext.getRequest(); String debugFlag = request.getParameter("debug"); if ((debugFlag != null) && (!debugFlag.equalsIgnoreCase("false"))) { return(EVAL_BODY_INCLUDE); } else { return(SKIP_BODY); } } } Handler Example (DebugTag.java) JavaServer Pages

  33. TagLib Descriptor FileWEB-INF/csajsp-taglib.tld <?xml version="1.0" encoding="ISO-8859-1" ?> <!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN" "http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd"> <taglib> <tlibversion>1.0</tlibversion> <jspversion>1.1</jspversion> <shortname>csajsp</shortname> <uri></uri> JavaServer Pages

  34. WEB-INF/csajsp-taglib.tld (Cont) <info> A tag library from Core Servlets and JavaServer Pages, http://www.coreservlets.com/. </info> <tag> <name>debug</name> <tagclass>corej2ee.examples.web.tag.DebugTag</tagclass> <bodycontent>JSP</bodycontent> <info>Includes body only if debug param is set.</info> </tag> </taglib> JavaServer Pages

  35. web.xml entry <?xml version="1.0" ?> <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN " "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd"> <web-app> <taglib> <taglib-uri>csajsp-taglib.tld</taglib-uri> <taglib-location>WEB-INF/csajsp-taglib.tld</taglib-location> </taglib> </web-app> JavaServer Pages

  36. <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <!-- Illustration of SimplePrimeTag tag. Taken from Core Servlets and JavaServer Pages from Prentice Hall and Sun Microsystems Press, http://www.coreservlets.com/. &copy; 2000 Marty Hall; may be freely used or adapted. --> <HTML> <HEAD> <TITLE>Using the Debug Tag</TITLE> <LINK REL=STYLESHEET HREF="JSP-Styles.css" TYPE="text/css"> </HEAD> <BODY> <H1>Using the Debug Tag</H1> <%@ taglib uri="csajsp-taglib.tld" prefix="csajsp" %> Top of regular page. Blah, blah, blah. Yadda, yadda, yadda. <P> <csajsp:debug> <B>Debug:</B> <UL> <LI>Current time: <%= new java.util.Date() %> <LI>Requesting hostname: <%= request.getRemoteHost() %> <LI>Session ID: <%= session.getId() %> </UL> </csajsp:debug> <P> Bottom of regular page. Blah, blah, blah. Yadda, yadda, yadda. </BODY></HTML> DebugExample.jsp JavaServer Pages

  37. Invoking debug.jsp JavaServer Pages

  38. Invoking debug.jsp with Debug JavaServer Pages

  39. Tag Complexity • Tags can become very complicated • Can parse body themselves • Can become nested in other tags • Ex. IF/THEN/ELSE • Looping constructs • While beans are generally used for model data and shared information, tags are typically confined to a single page JavaServer Pages

  40. Tag Summary • Tags are a portable extension mechanism for jsp • Can build a library of components • Ex. XSLT renderer of XML data • Bridge to JavaBean model data • Ex. Setting indexed properties • Further eliminates the need for HTML authors to learn Java JavaServer Pages

  41. JSTL and Expression Language Optional Topic JavaServer Pages

  42. JSP Standard Tag Library • Encapsulates core functionality for many web applications in custom tags • http://java.sun.com/products/jsp/jstl • Requires JSP 1.2 • Custom tags • Iteration, Control, Internationalization, Database Access • Expression language to simplify page development JavaServer Pages

  43. JSTL Libraries • Core • XML Processing • I18N • Database Access JavaServer Pages

  44. Expression Language • Simpler syntax for accessing Java Bean properties • Similar to JavaScript • ${customerBean}.name$ • ${customerBean}[“name”]}$ • customerBean is in one of the JSP’s scopes • page, request, session, or application • Implicit variables also available • param – collection of all request parameters • cookie – collection of all cookies • header – collection of all request headers JavaServer Pages

  45. Basic Example (e1.jsp) <%@ taglib uri="myTLD" prefix="c" %> <html> <head> <title>JSTL: Basic EL Support</title> </head> <body bgcolor="#FFFFFF"> JavaServer Pages

  46. <h1>Basic EL examples</h1> ${cookie.JSESSIONID.value}: <c:out value="${cookie.JSESSIONID.value}" /> <BR> ${param['name']}: <c:out value="${param['name']}" /> <BR> ${header['User-Agent']}: <c:out value="${header['User-Agent']}" /> <BR> </body> </html> JavaServer Pages

  47. JavaServer Pages

  48. Iteration Example (IterateSetup.jsp) <%@ page import="corej2ee.examples.web.jspstl.*, java.util.List, java.util.ArrayList" %> <% STLPerson person=new STLPerson(); person.setName("Dan"); person.setStreet("Poplar Ridge"); person.setZip("21122"); JavaServer Pages

  49. STLPerson person2=new STLPerson(); person2.setName("Jim"); person2.setStreet("Severna Park"); person2.setZip("21046"); List peopleList=new ArrayList(); peopleList.add(person); peopleList.add(person2); request.setAttribute("people", peopleList); %> <jsp:include page="Iterate.jsp" /> JavaServer Pages

  50. Iterate.jsp <%@ taglib uri="myTLD" prefix="c" %> <html> <head> <title>JSTL: Iteration Example</title> </head> <body bgcolor="#FFFFFF"> <h3>Simple Iteration</h3> <h4>People list</h4> JavaServer Pages

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