1. Java Server Pages

2. Java Server Pages • Servlets are nice, but… • It’s a pain to put in all those out.println stmts • JSPs mix Java and HTML • Within the same document • Nice for team based projects • Web page designers don’t need to know Java • Programmers don’t need to know design

3. My First JSP <html> <head> <title>Greetings</title> </head> <body> <% for(int i=0;i<8;i++) { %> <p><font size=<%=i%>>Hello World!</font> <% } %> </body> </html> http://clotho/~snell/TestApps/HelloWorld.jsp

4. Java Server Pages • Allow you to insert code into the HTML • Expressions <%= expression %> • Scriptlets <% code %> • Declarations <%! code %> • Upon access, the JSP is converted to a servlet then executed • Same life cycle as a servlet

5. JSP Expressions • <%= Java Expression %> • Evaluated, Converted to a string, Inserted • Current Time: <%= new java.util.Date() %> • Predefined Variables • request the HttpServletRequest • response the HttpServletResponse • session the HttpSession • out the PrintWriter • application the ServletContext • config the ServletConfig • pageContext the PageContext

6. JSP Code • <% code %> • Just executed • <% for(int j = 0; j < 8; j++) { %> <p><font size=<%= j %>>Hi</font> <% } %> • <%-- JSP Comment --%> • <!– HTML Comment -->

7. JSP Declarations • <%! Code %> • Variable declarations • <%! private int accessCount = 0; %> Accesses: <%= ++accessCount %> • Variables have class scope • Shared between all instances

8. XML Syntax • Expressions • <jsp:expression> Expression </jsp:expression> • Scriptlets • <jsp:scriptlet> Code </jsp:scriplet> • Declarations • <jsp:declaration> Code </jsp:declaration>

9. JSP directives • Affect the overall structure of the page • <%@ directive attribute=“value” %> • The page directive • <%@ page import=“java.util.*” %> • <%@ page contentType=“text/plain” %> • <%@ page session=“true” %> <%-- default --%> • The include directive • <%@ include file=“Navbar.jsp” %> • Translation time • <jsp:include page=“Navbar.jsp” flush=“true”/> • Request time

10. Java Beans • What is a bean? • Data structure that conforms to certain rules • Bean rules • Must have a zero argument constructor • No public instance variables • Persistent values set/accessed through • setXxx • getXxx • Mostly used for persistent storage of data

11. Bean Usage • <jsp:useBean id=“name” class=“pkg.class” /> • Similar to: • <% name = new pkg.class(); %> • More powerful • Scope (page, application, session, request) • Bean Location • Must be in server’s regular class path

12. Bean Usage • Getting values • <jsp:getProperty name=“className” property=“variableName” /> • Setting values • <jsp:setProperty name=“className” property=“variableName” value=“The String Value” /> • Or param=“NumberVariable” />

13. My First Bean public class MessageBean { private String message = "No String Specified"; public String getMessage() { return (message); } public void setMessage(String theMessage) { message = theMessage; } }

14. The JSP … <jsp:useBean id="myBean" class="MessageBean" scope="session" /> <ol> <li>Initial Value: <i><jsp:getProperty name="myBean" property="message" /></i> <jsp:setProperty name="myBean" property="message" value="Howdy" /> <li>After jsp:setProperty : <i><jsp:getProperty name="myBean" property="message" /></i> <% myBean.setMessage("After Scriptlet"); %> <li>After scriptlet : <i><%= myBean.getMessage() %></i> </ol> http://clotho/~snell/TestApps/MessageBean.jsp

15. Custom JSP Tags • Tags encapsulate complex behaviors • Make them simple and accessible • Tags are essentially function calls to Java code • Consist of two pieces • The Tag Handler (Java code) • Defines the action • The Tag Library Descriptor (xml) • Identifies the tag to the server

16. My First Custom JSP Tag Handler import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; import java.io.*; // Simple JSP tag that just inserts the string "Simple Example Tag" public class SimpleTagExample extends TagSupport { public int doStartTag() { try { JspWriter out = pageContext.getOut(); out.print("Simple Example Tag"); } catch(IOException ioe) { System.out.println("Error in ExampleTag"); } return(SKIP_BODY); } }

17. The Tag Library Descriptor <?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>simpletag</shortname> <urn></urn> <info> My tag example. </info> <tag> <name>example</name> <tagclass>SimpleTagExample</tagclass> <info>Simple example</info> <bodycontent>EMPTY</bodycontent> </tag> </taglib>

18. The JSP <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transistional//EN"> <html><head> <%@ taglib uri="simpletagexample-taglib.tld" prefix="simpletag" %> <title><simpletag:example /></title> </head> <body> <h1><simpletag:example /></h1> Here is the output from the tag: <i><simpletag:example /></i> </body> </html> http://clotho/~snell/TestApps/SimpleTagExample.jsp