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JSP

JSP. Michelle Johnston, Firebird Services Ltd. JSP Pages. HTML page can become a jsp just by changing the extension to jsp Allows java to be run within HTML pages. Directives. <%@page language="java" %> <%@ include file="/header.jsp" %> <%@ taglib uri="tlds/taglib.tld" prefix="mytag" %>

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JSP

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  1. JSP Michelle Johnston, Firebird Services Ltd

  2. JSP Pages • HTML page can become a jsp just by changing the extension to jsp • Allows java to be run within HTML pages

  3. Directives • <%@page language="java" %> • <%@ include file="/header.jsp" %> • <%@ taglib uri="tlds/taglib.tld" prefix="mytag" %> • <%@page language="java" import="java.sql.*,mypackage.myclass" %> • <%@page language="java" session="true" %> • <%@page language="java" session="true" errorPage="error.jsp" %> • <%@page language="java" session="true" contentType="text/html;charset=ISO-8859-1" %>

  4. Declaratives • Declarations are embedded within <!%= …%> • <%@ page import="java.util.*" %> • <HTML> • <BODY> • <%!     • Date theDate = new Date();     • Date getDate()     • {         • System.out.println( "In getDate() method" );         • return theDate;     • } • %> • Hello!  The time is now <%= getDate() %> • </BODY> • </HTML>

  5. Declaratives • Here we are declaring a variable theDate • And the method getDate() • Both will now be available in our scriptlets • Warning! Declarations/declaratives are only evaluated ONCE per page – reload and the date remains the same!

  6. Request method • Get request info • <%=request.getMethod()%> • <%=request.getRequestURI()%> • <%=request.getProtocol()%> • <%=request.getPathInfo()%> • <%=request.getQueryString()%>

  7. Changing Date value • <HTML> • <BODY> • Hello!  The time is now <%= new java.util.Date() %> • </BODY> • </HTML> • Refresh the above page and see the date change!

  8. Exercise 1 • Exercise: Write a JSP to output the values returned by • System.getProperty for various system properties such as • java.version, java.home, os.name, user.name, user.home, user.dir etc.

  9. Scriptlets • Get a parameter • <% • //java code • String userName=null; • userName=request.getParameter("userName"); • %>

  10. Scriptlets • <HTML> • <BODY> • <% • // This is a scriptlet. Notice that the "date" • // variable we declare here is available in the • // embedded expression later on. • System.out.println( "Evaluating date now" ); • java.util.Date date = new java.util.Date(); • %> • Hello! The time is now <%= date %> • </BODY> • </HTML>

  11. Outputting Info • Note that System.out.println writes to stdout (console) • To write to the html page, we put the value in <%= %> • Another way would be to use out (an object 'given' to you that allows you to write to html)

  12. Outputting Info • <HTML> • <BODY> • <% • // This scriptlet declares and initializes "date" • System.out.println( "Evaluating date now" ); • java.util.Date date = new java.util.Date(); • %> • Hello! The time is now • <% • // This scriptlet generates HTML output • out.println( String.valueOf( date )); • %> • </BODY> • </HTML>

  13. Exercise 2 • Exercise:  Write a JSP to output the entire line, "Hello!  The time is now ..." but use a scriptlet for the complete string, including the HTML tags.

  14. Using Tables • <TABLE BORDER=2> • <%     • for ( int i = 0; i < n; i++ ) • { •   %>         • <TR> •         <TD>Number</TD>         • <TD><%= i+1%></TD> •   </TR>         • <%     • } • %> • </TABLE>

  15. Exercise 3 • Write a JSP to output all the values returned by System.getProperties with "<BR>" embedded after each property name and value.  Do not output the "<BR>" using the "out" variable.

  16. Directives • Don’t fully qualify classes, import them! • <%@ page import="java.util.*" %> • <HTML> • <BODY> • <%     • System.out.println( "Evaluating date now" );     • Date date = new Date(); • %> • Hello!  The time is now <%= date %> • </BODY> • </HTML>

  17. Importing • To import more than one package, simply comma separate them.. • <%@ page import="java.util.*,java.text.*" %>

  18. Includes • Include puts the full text of the included file embedded into the jsp file (can be html/jsp/anything) • <HTML> • <BODY> • Going to include hello.jsp... • <BR> • <%@ include file="hello.jsp" %> </BODY> • </HTML>

  19. Tags • < not <% • <some:tag> body </some:tag> • <some:tag/> (no body to this tag – xml like) • Predefined tags <jsp:.. • <HTML> • <BODY> • Going to include hello.jsp... • <BR> • <jsp:include page="hello.jsp"/> • </BODY> • </HTML>

  20. Exercise 4 • Change the jsp:include to jsp:forward and note the difference. • Write a JSP to do either a forward or an include, depending upon a boolean variable (hint:  The concepts of mixing HTML and scriptlets work with JSP tags also!)

  21. Calling JSP in Forms • <HTML> • <BODY> • <FORM METHOD=POST ACTION="SaveName.jsp"> • What's your name? • <INPUT TYPE=TEXT NAME=username SIZE=20> • <P><INPUT TYPE=SUBMIT> • </FORM> • </BODY> • </HTML>

  22. Creating a session • SaveName.jsp saves the name in a session: • <%    String name = request.getParameter( "username" );    • session.setAttribute( "theName", name ); • %> • <HTML> • <BODY> • <A HREF="NextPage.jsp">Continue</A> </BODY> • </HTML>

  23. Retrieving Session Info • NextPage.jsp shows how to retrieve the saved name. • <HTML> • <BODY> • Hello, <%= session.getAttribute( "theName" ) %> • </BODY> • </HTML>

  24. Exercise 5 • Add another attribute age to the whole of this example (all three pages)

  25. Form Processing • Add email and age to the form in GetName.html • <HTML> • <BODY> • <FORM METHOD=POST ACTION="SaveName.jsp"> • What's your name? • <INPUT TYPE=TEXT NAME=username SIZE=20><BR> • What's your e-mail address? • <INPUT TYPE=TEXT NAME=email SIZE=20><BR> • What's your age? • <INPUT TYPE=TEXT NAME=age SIZE=4><P> • <INPUT TYPE=SUBMIT> • </FORM> • </BODY> • </HTML>

  26. Using Beans • Create a bean (Java class) with username, email and age as fields • Create setter methods (setUsername, setEmail and setAge) • Create getter methods (getUsername, getEmail and getAge)

  27. UserData class • public class UserData {    • String username;     • String email;     • int age;     • public void setUsername( String value)     • {         • username = value;     • }     • public void setEmail( String value )     • {         • email = value;     • }    

  28. UserData Class cont • public void setAge( int value )     • {         age = value;     • }     • public String getUsername() • { return username; }     • public String getEmail() • { return email; }     • public int getAge() • { return age; } • }

  29. Bean Compilation • Compile bean • Put in the classpath of web server • Now let us change "SaveName.jsp" to use a bean to collect the data. • <jsp:useBean id="user" class="UserData" scope="session"/> • <jsp:setProperty name="user" property="*"/>  • <HTML> • <BODY> • <A HREF="NextPage.jsp">Continue</A> </BODY> • </HTML>

  30. Retrieving Bean Data • Let us modify NextPage.jsp to retrieve the data from bean.. • <jsp:useBean id="user" class="UserData" scope="session"/>  • <HTML> • <BODY> • You entered<BR> • Name: <%= user.getUsername() %><BR> • Email: <%= user.getEmail() %><BR> • Age: <%= user.getAge() %><BR> • </BODY> • </HTML>

  31. Exercise 6 • 1)  Write a JSP/HTML set that allows a user to enter the name of a system property, and then displays the value returned by System.getProperty for that property name (handle errors appripriately.)   • 2)  Go back to the exercises where you manually modified boolean variables.  Instead of a boolean variable, make these come from a HIDDEN form field that can be set to true or false.

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