Cocoon Flow. Tuomo Lesonen T WWW Applications

Transcription

1 Cocoon Flow Tuomo Lesonen T WWW Applications

2 Introduction to Cocoon An XML-based framework for building web applications Many resusable components (blocks), easy to build Lego -like solutions Powerful Java-interfaces for extending with custom components

3 Separation of Concerns Web development is all about separation of concerns: Logic, content and style should not be mixed -> leads to bad programming and maintainability! Cocoon does this efficiently by defining different types of components and application layers for these areas

4 Component Pipelines A request goes through a pipeline, where it s processed and finally served to the client Different pipeline components: generators, matchers, selectors, readers, actions, transformers, serializers Data is first generated, then transformed n times and serialized to preferred type

5 Pipeline example Basic scenario: Request is received by a pipeline,, an XML-file is read from a disc, transformed to HTML and then served back to client

6 Sitemaps Pipelines are stored in XML-files called sitemaps In addition, pipeline components are introduced and configured in sitemaps Sitemaps can be mounted for modularity

7 Virtual URI-space (optional) Requested addresses are mapped in sitemaps virtually -> /products products can be matched to serve a page containing current products in a database Parts of URI:s can be matched and used later in the pipeline: : /products products/*/ /*/specs will match any product,, and {1} can be substituted to get that product s info from database

8 Controlling Application Flow #1 Modern web application works like a traditional desktop application Development differs greatly: : Web applications are typically modelled as finite state machines: application is in one state at a time FSM-model works for simple cases, but as application grows, number of states grow too, which makes it hard to see what s happening inside the application HTTP has limitations, can we live with them?

9 Controlling Application Flow #2 Cocoon allows writing web applications as traditional programs, while honouring HTTP Idea of continuations borrowed from functional languages like Scheme Flow Script for programming the application logic Cocoon has an enhanced MVC (Model( Model-View- Controller) architecture

10 Controlling Application Flow in Other Frameworks J2EE MVC model 1: No centralized control, JSP- pages mix logic with presentation and add complexity J2EE MVC model 2: Controller servlet,, a better aproach, but issues such as back back button not resolved. Changes need recompiling and restarting the servlet container Apache Struts: : Port of Cocoon Flow, slow development lately? RIFE: Integrated support for continuations, uses Java as the flow language

11 MVC #1 (decentralized( control)

12 MVC #2 (decentralized( control)

13 MVC #3 (centralized( control)

14 MVC #4 (centralized( control + continuations)

15 Continuations in Cocoon Continuation is an object which holds a snapshot of a state in an application (stack trace, program counter, local variables) Web application can have multiple states (multiple continuations) Continuations are kept in a tree structure with relationships When input needed from user, continuation created and saved and ID passed to view-layer (execution pauses) Execution is later restored from a continuation with the ID

16 Flow Script Logic is written with Flow Script Cocoon has built-in in support for Javascript, other languages can be easilly added (Scheme,, Java etc.) Business logic is called within flow script sendpageandwait(uri,, data) and sendpage(uri,, data) functions provided Flow Script itself is invoked from sitemap

17 Flow Script Example function calculator() { var a, b, operator; cocoon.sendpageandwait("geta.html"); "); a = cocoon.request.get("a"); cocoon.sendpageandwait("getb.html"); "); b = cocoon.request.get("b"); cocoon.sendpageandwait("getoperator.html"); "); operator = cocoon.request.get("op"); try { if (operator == "plus") cocoon.sendpage("result.html", ", {result: a + b}); else if (operator == "minus") cocoon.sendpage("result.html", ", {result: a - b}); else if (operator == "multiply") cocoon.sendpage("result.html", ", {result: a * b}); else if (operator == "divide") cocoon.sendpage("result.html", ", {result: a / b}); else cocoon.sendpage("invalidoperator.html", ", {operator: operator}); } catch (exception) { cocoon.sendpage("error.html", ", {message: "Operation failed: " + exception.tostring()}); } }

18 The View Layer An XML-based template language for creating views (pages) provided JeXL and JXPath (similar to XPath) supported Works great with the flow layer (parameters in/out) Predefined tags for conditions (if, choose), variables (local, global), loops, macros etc. Flow Script variables can be read in to output dynamic pages

19 JXTemplate example #1 <?xml version="1.0"?> <html xmlns:jx=" <head><title>cocoon flow number guessing game</title></head> <body> <h1>success!</h1> <h2>the number was: ${random}</h2> <h3>it took you ${guesses} tries.</h3> <p><a href="./">play again</a></p> </body> </html>

20 JXTemplate example #2 <?xml version="1.0"?> <html xmlns:jx=" <head><title>people who work here</title></head> <body> <jx:foreach select= #{employee} > <p>name: #{./firstname firstname} } #{./lastname lastname}</p> </jx:foreach jx:foreach> </body> </html>

21 Conclusion Cocoon Flow helps building and maintainting complex (large) web applications Model, view and controller layers kept nicely separated Underlaying protocols and standards can co- exist Developing modern web applications closer to traditional programming