![Wrapper - Concrete Process Steps
Full process cycle
HTTP/1.1 200 OK
Last-Modified: Wed, 01 Dec 2010
Local-name(/*[1]) = task
Content-Type: application/xml
/task/status/text() = defined
<task>
<id>04</id>
<name>Update Database</name>
<status>defined</status>
<parentStory>08</parentStory>
</task>
HTTP/1.1 200 OK
/task/id/text() = 04
Last-Modified: Wed, 01 Dec 2010
URI-Templates /task/parentStory/text() = 08
Content-Type: application/xml
Link: </stories/08/tasks/04/block>;rel=”Task.block”
Link: </stories/08/tasks/04/begin>;rel=”Task.begin”
Link: </stories/08/tasks>; rel=”Task.allTasks”
Link: </stories/08>; rel=”belongs_to_story”
Task.block: </stories/08/tasks/04/block>
<task>
Task.begin: </stories/08/tasks/04/begin>
<id>04</id>
Task.allTasks: </stories/08/tasks>
<name>Update Database</name>
Belongs_To_Story: </stories/08>
<status>defined</status>
<parentStory>08</parentStory>
</task>
Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 19](https://image.slidesharecdn.com/s2-liskin-110330160645-phpapp02/85/Teaching-Old-Services-New-Tricks-Adding-HATEOAS-Support-as-an-Afterthought-19-320.jpg)
Teaching Old Services New Tricks: Adding HATEOAS Support as an Afterthought
- 1. Teaching Old Services New Tricks: Adding HATEOAS Support as an Afterthought Olga Liskin, Leif Singer, Kurt Schneider {olga.liskin, leif.singer, kurt.schneider} @inf.uni-hannover.de 28.03.2011
- 2. Content Motivation Main Goals Service Example Terminology Notation for Application Models Conception of Wrapper Component Comparison Conclusions & Outlook Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 2
- 3. Motivation Problem with web service communication: Client needs to know exactly, what a request has to look like Many sources for errors – Coding errors – Invalid requests Idea: Server includes request-information in response messages – Which requests allowed next – What they look like HATEOAS But: not many services conform to this principle Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 3
- 4. Motivation Example: Service response without HATEOAS: HTTP/1.1 200 OK What can the client Last-Modified: Wed, 01 Dec 2010 17:36:02 GMT next? do Content-Type: application/xml <task> <id>208</id> <name>create GUI</name> No idea. The client <status>inprogress</status> has to know by itself. <parentStoryId>04</parentStoryId> </task> Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 4
- 5. Motivation Example: Service response with HATEOAS: HTTP/1.1 200 OK Last-Modified: Wed, 01 Dec 2010 17:36:02 GMT Control elements Content-Type: application/xml directly present in Link: <stories/04/tasks/208/finish>; rel=“finish” response message. Link: <stories/04/tasks/208/block>; rel=“block” <task> <id>208</id> Now client can see <name>create GUI</name> following requests <status>inprogress</status> and how to make them <parentStory>/stories/04</parentStory> </task> …and also indicate this Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 5
- 6. Main Goals Create HATEOAS support using state charts – Automatically generate a wrapper Service Information Generator/ Wrapper Interpreter Developer Client Wrapper Server Prerequisite: Clear way to model network-based applications – State Charts – Terminology Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 6
- 7. Service Example Backlog service: support agile development projects Backlog – contains story cards Story Card – One particular topic – Different states „definde“, „in progress“, „blocked“,… Depend on included tasks Task – Story Card divided into tasks – Different states Changed by user Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 7
- 8. 1 Modelling Network-Based Applications Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 8
- 9. Terminology Valid requests depend on current application state What exactly is application state? Relevant terminology: – application „representation of the business-aware functionality of a system“ (Fielding) – resource state Values of a resource‘s attributes – application state Requests, responses and the processing of those E.g.: „process detail view of a story card“ Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 9
- 10. Terminology 31 finished Backlog 08 24 blocked New idea: Story – Equivalence classes of application states Combine „similar“ states Determined by resource class and resource state Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 10
- 11. State Chart States – Equivalence classes of application states – Composite States combine states with same resource class Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 11
- 12. State Chart Transitions – Possible change of application state triggered by new client request – Target state reached in case of success Transitions between Simple States Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 12
- 13. State Chart Transitions between Composite States – More precise information about control flow necessary – Outgoing transition: Transition possible from all sub-states – Incoming transition: Client requests a resource of particular class Sub-state can only be determined at runtime choice-pseudostate Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 13
- 14. State Chart Simplified notation – Remove end vertex – Remove choice pseudostate construct Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 14
- 15. State Chart Use State Chart as a static map Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 15
- 16. 2 Constructing A Wrapper Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 16
- 17. Wrapper - Conception Top-Down view – Wrapper at first as black-box Insert wrapper between client and server Request Request Client Wrapper Server HATEOAS- Response Response Response – Request forwarded – Response enriched with transitions But not changed further Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 17
- 18. Wrapper - Conception Main process Request Wrapper Request Forward request 1 Request Request Enrich response Response Calculate application state 2 application state <<datastore>> transitions Look up Transition model transitions HATEOAS- 3 valid Response HATEOAS- transitions Response Response Construct links 4 Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 18
- 19. Wrapper - Concrete Process Steps Full process cycle HTTP/1.1 200 OK Last-Modified: Wed, 01 Dec 2010 Local-name(/*[1]) = task Content-Type: application/xml /task/status/text() = defined <task> <id>04</id> <name>Update Database</name> <status>defined</status> <parentStory>08</parentStory> </task> HTTP/1.1 200 OK /task/id/text() = 04 Last-Modified: Wed, 01 Dec 2010 URI-Templates /task/parentStory/text() = 08 Content-Type: application/xml Link: </stories/08/tasks/04/block>;rel=”Task.block” Link: </stories/08/tasks/04/begin>;rel=”Task.begin” Link: </stories/08/tasks>; rel=”Task.allTasks” Link: </stories/08>; rel=”belongs_to_story” Task.block: </stories/08/tasks/04/block> <task> Task.begin: </stories/08/tasks/04/begin> <id>04</id> Task.allTasks: </stories/08/tasks> <name>Update Database</name> Belongs_To_Story: </stories/08> <status>defined</status> <parentStory>08</parentStory> </task> Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 19
- 20. Comparison Implementation of backlog service Automated generation of wrapper (from transition model) Develop 2 clients to test concepts – With wrapper <-> without wrapper List links = if(story.getStatus().equals(StoryStatus response.getHeaders().get("Link"); .Defined)){ for(String link : links){ this.startButton.setEnabled(true); if(link.contains("story.start")){ this.startButton.setUri("/stories/"+ String uri = extractUri(link); story.getId() + "/start"); this.startButton.setUri(uri); this.blockButton.setEnabled(true); this.startButton.setEnabled(true); this.blockButton.setUri("/stories/"+ }//... story.getId() + "/block") } } Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 20
- 21. Conclusions Creation of theoretical concepts Development of wrapper process Check the concept Is working Generic Improves development and maintainance of clients Errors in model lead to invalid/missing links Input data is complex Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 21
- 22. Outlook Further research on input of data – Project environment – Interface descriptions (e.g. WADL) as additional source Allow changes of whole service API – Can improve more REST aspects Use state charts for creation of services (not only wrappers) Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 22
- 23. Content Motivation Main Goals Service Example Terminology Notation for Application Models Conception of Wrapper Component Comparison Conclusions & Outlook Questions? Teaching Old Services New Tricks – Olga Liskin, Leif Singer, Kurt Schneider 28.03.2011 23