Java Server Pages An introduction to JSP

Containers and Components Several clients – one system

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

JSP – Directives At the top of a JSP page, the page directive is used 

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

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

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

Other Directives Include directive   Includes the file BEFORE compilation  Only static content

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()

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

JSP – Implicit objects exception  Only in error pages  getMessage()  printStackTrace()

Java Code Three ways to use Java Code in your JSP  Declares member variables  NOT thread safe  Used to print single expressions

Java Code  Can contain the entire application  Use with care  Can give very hard to read code <% if(status == 1) { %> Yo <%} Else{ %> Oy

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

Forward Forwards the request

Include Includes the output in runtime Can be dynamic content

UseBean Used to initialize a bean. Only called once The bean is created

GetProperty Used to call getXXX methods in a bean  Will call bean.getName()  Name is the same as id in

SetProperty Used to call setXXX methods in a bean When * is used as property name, a setXXX for value in getParameterNames() will be called

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; }

Example cont. The bean is created