Java Server Pages

1. Java Server Pages An introduction to JSP

2. Containers and Components • Several clients – one system

3. Java Server Pages (JSP) • HTML with embedded Java code • Good for presentation • No print statements • Compiled to a Servlet at runtime • Good performance • Easy deployment • When a JSP is updated it’s recompiled • Possible to compile manually • Easy for web designers to use • Edited in an ordinary HTML editor • Support for Java Beans and Custom tags

4. JSP – Directives • At the top of a JSP page, the page directive is used • <%@ page name=“value” %>

5. JSP – Page Directive parameters • language • Default is java • extends • Default is the base JSP class, but you could use your own • import=“package1,package2, class1, class2” • session • True or False, determines if sessions should be automatically created. True is default

6. JSP – Page Directive parameters • buffer • The output buffer size • autoFlush • True or false, determines if the output should be flushed to the client. True is default • isThreadSafe • True or false. True is default • info • Descriptive text

7. JSP – Page Directive parameters • errorPage • The page to go to in case of an error • contentType • isErrorPage • Defines if this is a error page. False is default. If it’s an error page a couple of extra objects are available in the page

8. Other Directives • Include directive • <%@ include file=“relative url” %> • Includes the file BEFORE compilation • Only static content

9. JSP – Implicit objects • In JSPs, a couple of objects are allways available • request • Subclass of ServletRequest • getParameter(), getParameterNames() • getAttribute() • … • Response • Subclass of ServletResponse • Not used in normal situations • pageContext • Used to get configuration variables for this page • getAttribute()

10. JSP – Implicit objects • session • The HttpSession • Created automatically if session is not false in the page directive • application • javax.servlet.ServletContext • Used to get information about the application • out • Used to print (in scriptlets) • clear(), clearBuffer(), flush() • config • javax.servlet.ServletConfig • getInitParameter(), getInitParameterNames() • page • exception

11. JSP – Implicit objects • exception • Only in error pages • getMessage() • printStackTrace()

12. Java Code • Three ways to use Java Code in your JSP • <%! Declaration %> • Declares member variables • NOT thread safe • <%= MyClass.printMessage() %> • Used to print single expressions

13. Java Code • <% any java code %> • Can contain the entire application • Use with care • Can give very hard to read code <% if(status == 1) { %> <h3>Yo</h3> <%} Else{ %> <h3>Oy</h3> <% } %>

14. JSP Tags • There are a couple of tags available and you can extend the tag set with your own tags • XML Syntax • Doesn’t distract HTML authoring tools

15. Forward • <jsp:forward page=“relative URL” /> • Forwards the request

16. Include • <jsp:include page=“relative url” flusth=“true/false” /> • Includes the output in runtime • Can be dynamic content

17. UseBean • <jsp:useBean id=“instance name” scope=“page|request|session|application” beanName=“package.class”|class=“package.class” /> • Used to initialize a bean. Only called once <jsp:useBean …> <h4>The bean is created</h4> </jsp:useBean>

18. GetProperty • Used to call getXXX methods in a bean • <jsp:getProperty name=“bean instance name” property=“name” /> • Will call bean.getName() • Name is the same as id in <jsp:useBean>

19. SetProperty • Used to call setXXX methods in a bean • <jsp:setProperty name=“instance name” property=“*|propertyname” value=“value” /> • When * is used as property name, a setXXX for value in getParameterNames() will be called

20. Example • package test1; • class TestBean{ • private String name; • private String surname; • public String getName(){ • return name; • } • public String getSurname(){ • return surname; • } • public void setSurname(String _surname){ • surname=_surname; • } • public void setName(String name=_name){ • name=_name; • } • }

21. Example cont. <%@ page languea=“java” session=“true” %> <jsp:useBean id=“tb” class=“test1.TestBean” scope=“session”> <i>The bean is created </i> <jsp:getProperty name=“tb” property=“name” /> <jsp:setProperty name=“tb” property=“name” value=“Fredrik” />