JSTL Lec - 43

Umair©2006, All rights reserved JSTL (ni) Acronym of  JavaServer Pages Standard Tag Library JSTL (like JSP) is a specification, not an implementation Official reference implementation  Development theme  No Scriptlets

Umair©2006, All rights reserved JSTL Overview (ni) JSTL tags are valid XML JSTL contains action (tags) for common tasks  Iteration  Session Tracking  Redirect  XML  SQL etc. Remember – the development theme is “no scriptlets”

Umair©2006, All rights reserved Organization of the platform Your application Java language Java Servlet API JavaServer Pages (JSP) JSTL Your web pages EL

Umair©2006, All rights reserved Why JSTL? (ni) JSTL tags provide a standard implementation for typical application functionality  Reusability  Avoid reinventing the wheel Another mechanism for avoiding the use of JSP scripting elements  EL considerably simple than Java

Umair©2006, All rights reserved JSTL & EL (ni) JSTL includes support for EL  To replace the JSP expressions EL is also standard part of JSP 2.0 EL can only be used in attributes of JSTL tags prior to JSP 2.0  With JSP 2.0 and onwards, it can be used anywhere in the document

Umair©2006, All rights reserved JSTL Tag libraries Composed of 4 standard tag libraries  Core Conditions, Control flow & variables access etc.  Internationalization / format Locale messages Text, numbers & date formation  XML XML parsing / processing  SQL Tags for accessing an SQL database

Umair©2006, All rights reserved Twin Tag Libraries JSTL comes in two flavors  Request Time (RT) version Dynamic attribute values are specified using JSP expression (i.e. )  Expression Language (EL) version Dynamic attribute values are specified using JSTL expression language (i.e. ${ expression } ) Why ?

Umair©2006, All rights reserved JSTL Tag libraries (cont.) LibraryURIPrefix Core c SQL sql Internationalization / Format fmt XMLhttp://java.sun.com/jsp/jstl/xml x EL based

Umair©2006, All rights reserved JSTL Tag libraries (cont.) LibraryURIPrefix Core c_rt SQL sql_rt Internationalization / Format fmt_rt XMLhttp://java.sun.com/jsp/jstl/xml_rt x_rt RT based

Umair©2006, All rights reserved Using JSTL Use taglib directive, as we used for custom tag library For example  To use EL based core tag library  To use RT based core tag library

Umair©2006, All rights reserved Working with Core Actions (tags)

Umair©2006, All rights reserved Core Tag Library Support actions  Manipulation of scoped variables  Output  Conditional logic  loops  URL manipulation  and Handling errors.

Umair©2006, All rights reserved Core Tag Library c:set [1]  Provides a tag based mechanism for creating and setting scope based variables  Syntax:  var  Specifies the name of the scoped variables  scope  page | request | session | application  Optional and defaults to page  value  Specifies the value to be bound to the variable  If evaluates to NULL, attribute/var will be removed if exist.

Umair©2006, All rights reserved Core Tag Library c:set [2]  Examples

Umair©2006, All rights reserved Core Tag Library Using c:set forJavaBeans & Map [1]  Syntax: <c:set target=“beanOrMap” property =“propertyOrKey” value = “value” /> Target must not be NULL If target is a bean, sets the value of the property, equivalent to If target is a Map, sets the value of the key

Umair©2006, All rights reserved Core Tag Library Using c:set forJavaBeans [2]  Example <jsp:useBean id=“person” class=“vu.PersonInfo” scope=“request” />

Umair©2006, All rights reserved Core Tag Library c:out [1]  Equivalent to JSP expression i.e.  Syntax:  value  Evaluates the value attribute and outputs the result as string  default  Prints it if the value attribute evaluates to null or empty string  Optional

Umair©2006, All rights reserved Core Tag Library c:out [2]  Examples: Is equivalent to: <% String no = request.getParameter(“num”); if (no == null ) System.out.println(no); %>

Umair©2006, All rights reserved Core Tag Library c:remove  Used to delete a scoped variable  Syntax:  Examples:

Umair©2006, All rights reserved Core Tag Library c:forEach [1]  Used for iteration purpose  Supports two different styles of iteration Iteration over an integer range Iteration over a collection

Umair©2006, All rights reserved Core Tag Library c:forEach [2] (ni)  Iteration over an Integer Range [1] Like java language’s for statement  Syntax: <c:forEach var=“name” begin=“expression” end=“expression” step=“expression” /> Body Content If omitted, by default 1

Umair©2006, All rights reserved Core Tag Library c:forEach [3] (ni)  Iteration over an Integer Range [2] Example: To generate squares corresponding to range of integer values

Umair©2006, All rights reserved Core Tag Library c:forEach [4]  Iteration over a Collection [1] Can loop down on arrays, strings, list & map etc. Syntax: Body Content ArrayList HashMap Arrays etc.

Umair©2006, All rights reserved Core Tag Library c:forEach [5]  Iteration over a Collection [2] Example: To iterate over a String array <% for(int i=0; i<messages.length; i++) { String message = messages[i]; %> <% } // end for %> JSP without JSTL JSP after JSTL

Umair©2006, All rights reserved Core Tag Library c:forEach [6]  Iteration over a Collection [3] Example: To iterate over a persons ArrayList, contains PersonInfo objects <% ArrayList persons = (ArrayList)request.getAttribute(“pList”) for(int i=0; i<persons.size(); i++) { PersonInfo p == (PersonInfo)persons.get(i); String name = p.getName(); %> <% } // end for %> JSP without JSTL Type cast needed JSP after JSTL Automatic Type Conversion to appropriate type

Exampole code Addressbook(MVC) using core tags netBeans project – jstl_ex2

Umair©2006, All rights reserved Core Tag Library (ni) c:if  Used to conditionally process the body content  Syntax: Body content  Example: a equals b

Umair©2006, All rights reserved Core Tag Library (ni) c:choose [1]  Enables mutually exclusive conditionals  Syntax: Body content ……………. Body content -- Must appear at-least once -- Only one is processed whose test evaluates to true -- Can appear at-most once -- Only execute if all tests evaluate to false

Umair©2006, All rights reserved Core Tag Library (ni) c:choose [2]  Example: a equal b a equal c Don’t know what ‘a’ equal

Umair©2006, All rights reserved Working with SQL Actions (tags)

Umair©2006, All rights reserved SQL Tag Library Support actions  To interact with relational databases  Issuing queries & updates  transactions etc.

Umair©2006, All rights reserved SQL Tag Library sql:setDataSource [1]  Used for specifying data source  Syntax: <sql:setDataSource driver=“driver_name” url = “url” user = “user” password =“pwd” />

Umair©2006, All rights reserved SQL Tag Library sql:setDataSource [2]  Example: To connect with Microsoft Access database <sql:setDataSource driver = “sun.jdbc.odbc.JdbcOdbcDriver” url = “jdbc:odbc:PersonDSN” user = “” password = “” />

Umair©2006, All rights reserved SQL Tag Library sql:query  Used to execute queries  Syntax: <sql:query sql = “expression” var = “name” scope = “scope” /> -- Results of query stored -- Optional attribute to specify where to store var

Umair©2006, All rights reserved SQL Tag Library sql:query [2]  Example: executing a simple select query & processing results <sql:query sql = “SELECT * FROM PersonInfo” var = “res” /> Contains results of query

Exampole code Addressbook(MVC) using core & sql tags netBeans project – jstl_ex

Umair©2006, All rights reserved SQL Tag Library (ni) Problems  Heinous violation of MVC design pattern DB code (i.e. raw SQL) doesn’t belong in the presentation layer

Insert slide that contains only jsp pages – addressbook using only jsp pages

Umair©2006, All rights reserved Bringing it all together (lec 45 slide) Java provides these mechanisms for internet programming  Applets  Servlets  Java Server pages Scripting elements JSP Standard Tag library JSTL Expression language Java Beans (Enterprise Java Beans) Ultimately leads to easier, faster, and more powerful web application development?