Struts J2EE web application framework “ Model 2 ” Model View Controller Controller Servlet Key features XML metadata Struts taglib Simplified form validation

Tools for this course Tomcat (J2EE server) Ant (build tool) NetBeans (IDE)

A basic web application struts-config.xml in WEB-INF application.properties Several.jar files from Struts and other Jakarta open source projects A modified web.xml, with taglib mappings for the Struts taglibs and possibly JSTL.

Struts MVC with Actions 1. Request is intercepted by controller 2. Form is data captured in an ActionForm 3. Form is data validated in ActionForm 4. Controller calls execute() method of appropriate Action class. 5. Method returns ActionForward of view component.

Struts flow

Important Struts classes ActionForm Capture form data Returns ActionErrors in validate() Action Process the request Forward to appropriate resource Returns ActionForward ActionForward Abstract reference to a resource

The Action class Extend org.apache.struts.action.Action Implement execute() method. Parameters: ActionMapping ActionForm HttpServletRequest HttpServletResponse Thows java.lang.Exception Returns an ActionForward Controller forwards request to this resource.

Standard Actions Struts provides standard Actions ForwardAction SuccessAction FindForwardAction Forwards based on presence of parameter DispatchAction Method executed is determined by parameter Requires code

Action Lab Review JSP pages in application Tasks: Create ActionMappings for JSPs in struts-config.xml Define Actions in struts-config.xml ForwardAction SuccessAction FindForwardAction Create a subclass of DispatchAction

ActionForms ActionForms are used to collect and validate data from a request, typically generated by an HTML form. ActionForms resemble Java beans. Getters and setters Both not required Setters can expose data to inadvertent/malicious manipulation

ActionForm validation ActionForms have a validate() method. If validation is requested, this method is called after the ActionForm is populated with the request data. The validate() method returns an ActionErrors object, which is a collection of error messages If form validation fails, the request is forwarded back to the input form. Failure is determined by the presence of one or more ActionError objects in the ActionErrors collection. If the input form was constructed using the appropriate Struts tags, the form data is filled in. The Struts taglib can be used to display ActionError messages to the user.

ActionErrors The application.properties file defines the application ’ s error messages. error.userid.required=You must enter a user id Using the ActionErrors ActionErrors errors = new ActionErrors(); errors.add ("userid", new ActionError("error.userid.required")); Use a tag on the JSP page containing the input form

ActionForm lab Augment the FindForwardAction from Lab 1 with an Action that checks the user id and password Action will forward to warning page if credentials are not valid Create an ActionForm that will validate the login form data Validation should fail if user id or password is blank

Database access Access to a database requires a Connection. Web applications require many concurrent DB connections Opening a DB connection is slow Connection pooling Request a Connection from the pool Use the Connection Return the Connection to the pool

Where to put the pool? Persistence code needs access to the connection pool Where should the application store the pool? The web application ’ s application scope? Object with static members JNDI

Directory context Java objects Referenced by name javax.naming.* Naming Aliases java:comp/env/jdbc/mydb

JNDI setup Modify Tomcat ’ s server.xml file Commercial servers usually have web interface to create connection pools Modify web.xml file Add element Other J2EE servers may require an additional XML file.

Using JNDI Get InitialContext object InitialContext ic = new InitialContext() Look up the DataSource object Object o = ic.lookup( “ java:comp/env/jdbc/mydb ” ); Cast the object to the required class DataSource ds = (DataSource) o; Combine the lookup and the cast in one line for more compact code. Context operations will throw javax.naming.NamingException

JNDI Lab Check that necessary JAR files are in Tomcat ’ s common/lib directory Modify Tomcat ’ s server.xml Set correct DB URL Set password and username Modify web application ’ s web.xml Edit index.jsp Edit SQL query Add code to fetch data from ResultSet Add code to display data