1. Case Study: The Design of a JSP Framework By Michael Alford malford@orbitz.com March 29, 2001

2. Acknowledgments Xqsite, Inc.Xqsite, Inc. –Zak Jacobson –John Koszarek –Nick.Vujasin –Greg Skudlarick Orbitz LLCOrbitz LLC

3. Web Development

4. Forces Quick and easy developmentQuick and easy development Simple to maintainSimple to maintain High performanceHigh performance

5. Quick and Easy Development Just get the damn thing out the door!Just get the damn thing out the door! Engineers vary widely in skill/experience.Engineers vary widely in skill/experience. –Make common case very simple. –Make difficult stuff easy to plug in. Mismatch: Graphic artists work visually, while engineers work with code.Mismatch: Graphic artists work visually, while engineers work with code. Reuse previously written code.Reuse previously written code.

6. Simple to Maintain Low complexity.Low complexity. Easily extensible with use of patterns.Easily extensible with use of patterns. Easily configurable.Easily configurable. Straightforward to debug & monitor.Straightforward to debug & monitor. –Judicious logging. –Dont impair app server tools.

7. High Performance Instantiate as few objects as possible.Instantiate as few objects as possible. Cache reusable objects.Cache reusable objects. Avoid Java reflection.Avoid Java reflection. Minimize synchronization.Minimize synchronization. Minimize indirection.Minimize indirection. Minimize dynamic content.Minimize dynamic content.

8. Common Practices

9. Custom Tags Tag HandlerTag Handler –Java code –Evaluates custom tags –Properties pageContextpageContext parent tagparent tag

10. Benefits of Custom Tags Eliminate Java code from HTML.Eliminate Java code from HTML. Greater separation of content from presentation.Greater separation of content from presentation. Promote consistency across site.Promote consistency across site. Reusable within context of a website.Reusable within context of a website.

11. Liabilities of Custom Tags Designers cannot work visually.Designers cannot work visually. –Inefficient iterative back-and-forth between designer and developer. –Custom modules for visual tool? Closely tied to HTML, limiting reusability.Closely tied to HTML, limiting reusability. Lower performance versus embedded code.Lower performance versus embedded code. No industry standard set of tags.No industry standard set of tags.

12. JSP Model 2 (Model-View-Controller variant)

13. Benefits of MVC Multiple views of same model.Multiple views of same model. Pluggable views and controllers.Pluggable views and controllers. Separation of development tasks.Separation of development tasks. Reuse potential.Reuse potential. Frameworks potential.Frameworks potential.

14. Liabilities of MVC Increased complexity.Increased complexity. Close coupling between view & controller.Close coupling between view & controller. Close coupling of views & controllers to a model.Close coupling of views & controllers to a model. Difficulty of using MVC with some web development tools.Difficulty of using MVC with some web development tools.

15. Document-View Combine View and ControllerCombine View and Controller MVC variantMVC variant Java Swings UIDelegateJava Swings UIDelegate

16. Xqsite Page Architecture Core Classes

17. Design Goals Fast to develop for the common tasks.Fast to develop for the common tasks. –Even at the cost of flexibility. –Most of a website is specific to a project. Simple.Simple. Pluggable services for the hard stuff.Pluggable services for the hard stuff. JSP 1.0.JSP 1.0.

18. Architectural Overview

19. Page Container of FieldsContainer of Fields Mediator between View and Business LayerMediator between View and Business Layer The use bean tag in JSP is simple and easy to use.The use bean tag in JSP is simple and easy to use.

20. Page Benefits Standardizes development team on a common design.Standardizes development team on a common design. Automates validation and formatting of various types of data.Automates validation and formatting of various types of data. Automates required field handling.Automates required field handling. Extensible - add new field types or services without modifying existing architecture.Extensible - add new field types or services without modifying existing architecture. Provides file uploading services.Provides file uploading services. Easily configurable page-specific, field-specific, and locale-specific error messages; can even use a properties file.Easily configurable page-specific, field-specific, and locale-specific error messages; can even use a properties file.

21. Page: Init & Control <jsp:useBean id="pageObject"<jsp:useBean id="pageObject" scope="request"scope="request" class="yourPageSubclass">class="yourPageSubclass"> pageObject.onLoad(pageContext);pageObject.onLoad(pageContext); onLoadonLoad –Calls initFields –Calls business layer depending on whether this is first view or a submission of form data.

22. Page: Example OnLoad With Validation public void onLoad(PageContext pageContext) throws Exception { super.onLoad(pageContext); // Check if submit button was pressed if (isButtonSelected("createAccount")) { // Process the state when createAccount is clicked if (isFormValid()) { // call business objects here } if (isButtonSelected("cancel")) { // Process the state when cancel is clicked redirect("/location/of/maybe/the/previous/page"); } else { // Users initial visit or reload of page // Typically do nothing here }

23. Submit form back to JSP " method="POST"> " method="POST">

24. Page: Buttons Radio buttonsRadio buttons > > CheckboxesCheckboxes > >

25. Page: Text Field and Error Messages String getErrorMessage(String key, String fieldName)String getErrorMessage(String key, String fieldName) String getRequiredMessage(String fieldName)String getRequiredMessage(String fieldName) JSP:JSP: ' required="true"> ' required="true">

26. Field Abstract Class abstract void validate();abstract void validate(); boolean isRequired();boolean isRequired(); boolean isValid();boolean isValid(); read/write properties:read/write properties: –Name –Description –Value –Invalid and Missing Messages

27. Field Subclasses ButtonFieldButtonField DateFieldDateField NumericFieldNumericField SelectFieldSelectField TextFieldTextField

28. Xqsite Page Architecture Minimizing the Designer/Engineer Conflict

29. PageGenerator Uses the HTML Parser sunlabs.brazil.handler.HtmlRewriterUses the HTML Parser sunlabs.brazil.handler.HtmlRewriter For every HTML page, creates a subclass of Page.For every HTML page, creates a subclass of Page. For every HTML input field, adds a Field to the Page subclass.For every HTML input field, adds a Field to the Page subclass. Stubs out the onLoad method of Page subclass.Stubs out the onLoad method of Page subclass. Creates JSP with most of the necessary code to access the Page.Creates JSP with most of the necessary code to access the Page.

30. HTML Layer Requirements Each input field must be named uniquely.Each input field must be named uniquely. Add a fieldType attribute to those fields that need to be specified less generically.Add a fieldType attribute to those fields that need to be specified less generically. –Will not adversely affect visual HTML editors. –Example: HTML Text field may have a fieldType attribute of DateField. Add a required attribute for those fields that the user is required to enter.Add a required attribute for those fields that the user is required to enter.

31. Xqsite Page Architecture Service Delegation

32. Interceptor Pattern Allows services to be added transparently to a framework and triggered automatically when certain events occur.Allows services to be added transparently to a framework and triggered automatically when certain events occur. Services are defined in a config file, and registered upon app startup.Services are defined in a config file, and registered upon app startup. Page class onLoad acts as central dispatcher, passing a Context object to services.Page class onLoad acts as central dispatcher, passing a Context object to services.

33. Context control Context object provides accessors for services to retrieve state information.Context object provides accessors for services to retrieve state information. Context object provides mutators so that services may modify request.Context object provides mutators so that services may modify request. Example: Authorization service forwards user to a login page by setting target on Context object.Example: Authorization service forwards user to a login page by setting target on Context object.

34. Possible Services File uploadFile upload ConfigurationConfiguration Authorization/AuthenticationAuthorization/Authentication ThrottlingThrottling LoggingLogging 3 rd -Party Integration3 rd -Party Integration

35. Applying Page Concepts to Current Industry Practices

36. Adopt Custom Tags All Field subclasses can be made into custom tag handlers.All Field subclasses can be made into custom tag handlers. PageGenerator creates a JSP of custom tags instead of embedded Java code.PageGenerator creates a JSP of custom tags instead of embedded Java code.

37. Adopt MVC Eliminate Page in favor of FrontControllerEliminate Page in favor of FrontController Make FrontController a Interceptor dispatcher.Make FrontController a Interceptor dispatcher. If using Struts, PageGenerator can create an ActionForm.If using Struts, PageGenerator can create an ActionForm.

38. Other Java-based Web Frameworks StrutsStruts WebMacro and VelocityWebMacro and Velocity HyperQbsHyperQbs JanxJanx WebWorkWebWork Cocoon (XSP)Cocoon (XSP) Resin (XTP)Resin (XTP) BrazilBrazil

39. References Crupi, Malks, Alur, Core J2EE Patterns, or http://developer.java.sun.com/developer/technical Articles/J2EE/patterns/ http://developer.java.sun.com/developer/technical Articles/J2EE/patterns/ http://developer.java.sun.com/developer/technical Articles/J2EE/patterns/ Gamma, et al.,(aka Gang of Four), Design Patterns Buschmann, et al., Pattern-Oriented Software Architecture; A System of Patterns Schmidt, et al., Pattern-Oriented Software Architecture; Patterns for Concurrent and Networked Objects Struts Framework, http://jakarta.apache.org/struts