Client-Server-Kommunikation mit dem Command Pattern
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The document discusses client-server communication using the command pattern, emphasizing key topics such as versioning, batching, caching, and scaling. It examines approaches and best practices to ensure type safety, maintainability, and efficient communication in web applications, particularly in the context of GWT-RPC and Java. Strategies for handling high traffic, including load balancing and stateless architecture, are also presented to optimize performance and avoid common bottlenecks.
Client-Server-Kommunikation mit dem Command Pattern
- 1. Client-Server-Kommunikation mit dem Command Pattern p.g.taboada | pgt technology scouting GmbH
- 2. Papick G. Taboada pgt technology scouting GmbH! http://pgt.de Orientation in Objects GmbH! http://oio.de
- 4. ‣ Client-Server communication ‣ Command pattern ‣ Versioning ‣ Batching, Caching ‣ Scaling
- 5. ! eb t w en sic pm las elo c v de Server Browser user action e ons html resp full user action po l html res ful nse user action po l html res ful nse
- 6. eb ent w IA pm R lo ve de Server Browser first reques t e l respons full htm event event event data reque st data event data reque data st
- 7. Honor the A in JAX does ‣ Javascript it not block ! Get over ‣ Latency is not a myth ‣ Results must not arrive in the call order
- 8. BUILDING A GENERIC FRAMEWORK FOR MARSHALLING/ UNSMARSHALLING DATA SUCKS
- 9. MARSHALLING / UNMARSHALLING IN JAVASCRIPT IS SLOW
- 10. DON‘T BIND YOU NEXT 3 YEARS OF WORK AGAINST SOME COMMUNICATION PROTOCOLL
- 11. LOADING TOO MUCH DATA WILL ALWAYS HURT
- 12. ‣ Client-Server communication ‣ Command pattern ‣ Versioning ‣ Batching, Caching ‣ Scaling
- 13. GWT-RPC is a good solution if handled with care GWT-RPC binds many methods into one interface SomeResult someMethodName(SomeParameter spo) Interface Versioning is a monstrous thing
- 14. this will be an object SomeResult someMethodName(SomeParameter spo) this will be an object too
- 15. the method names bind the requests to the result SomeResult someMethodName(SomeParameter spo) typesafety all the way
- 16. USING GENERICS FOR ! TYPESAFETY, ! GET RID OF METHODS ! AND INTERFACES
- 17. now we just one interface with one method <A extends Action<R>, R extends Result> R execute(A action); typesafety all the way
- 18. ! command pattern GOF Pattern ! commonly used in Rich Clients !
- 22. client server Java client someAction RMI / HTTPInvoker someActionHandler someResult batching caching security caching exception translation security
- 24. aka DTOs type safety Reusable public class TerminLoadAction implements Action<DataResult<TerminData>> { ! ! ! } public class DataResult<DATA extends Data> implements Result { ! private String terminId; public TerminLoadAction(String terminId) { this.terminId = terminId; } ! ! public String getTerminId() { return terminId; } ! ! private DATA data; public DataResult(DATA data) { this.data = data; } public void setData(DATA data) { this.data = data; } public DATA getData() { return data; } } Action Result
- 25. <A extends Action<R>, R extends Result> void execute(A action, AsyncCallback<R> callback) dispatch.execute( ! new TerminLoadAction(terminId), new AsyncCallback<DataResult<TerminData>>() { ! @Override public void onFailure(Throwable caught) { } ! ! ! ); @Override public void onSuccess(DataResult<TerminData> result) { } }
- 26. Server side type safety handler to action mapping public interface ActionHandler <A extends Action<R>, R extends Result> { ! ! ! ! ! action execution Class<A> getActionType(); R execute( A action, ExecutionContext context) throws DispatchException; ! } declared exception hiearchy Execution context for server side command execution
- 27. Server side custom annotation spring @ActionHandlerBean @Transactional public final class TerminDataLoadHandler implements ActionHandler<TerminLoadAction, DataResult<TerminData>> { ! access to backend type safe result ! ! ! ! ! ! ! } @Autowired private TerminDAO terminDao; @Override public DataResult<TerminData> execute( TerminLoadAction action, ExecutionContext context) throws DispatchException { TerminBean termin = … TerminData data = … return new DataResult<TerminData>(data); } @Override public Class<TerminLoadAction> getActionType() { return TerminLoadAction.class; } business logic, etc…
- 28. ‣ Client-Server communication ‣ Command pattern ‣ Versioning ‣ Batching, Caching ‣ Scaling
- 30. easy way right way? public interface SomeNiceService extends RemoteService { ! ! ! String someService(String param); String someServiceV2(String param); String someServiceV3(String param); } public interface SomeNiceService extends RemoteService { ! ! String someService(String param); } ! public interface SomeNiceServiceV2 extends RemoteService { ! ! String someService(String param); } maintainability? maintainability? ! public interface SomeNiceServiceV3 extends RemoteService { ! ! } String someService(String param);
- 32. different versions can coexist! someAction someActionV2 multiple versions someActionHandler someActionHandlerV2 someResult same result
- 34. ‣ Client-Server communication ‣ Command pattern ‣ Versioning ‣ Batching, Caching ‣ Scaling
- 35. why batch?
- 36. • one batch call is better than 10 single calls • less data • less roundtrip latency • avoid connection bottleneck • ensure server side execution order • less roundtrips solving common problems
- 37. someAction1 client server someAction2 batchActionHandler someAction3 someAction1 batchAction someAction2 batchResult someAction3 someResult1 someResult2 someResult3 batching can server executes be manual or actions in given order automatic
- 39. IDLE Scheduler.scheduleEntry(…) GWT code execution Scheduler.scheduleFinally(…) browser event loop Scheduler.scheduleDeferred(…)
- 40. IDLE collect commands GWT code execution Scheduler.scheduleFinally(…) cmd 1! cmd 2! cmd 3! cmd … fire batch command
- 41. BATCH EXECUTION ALLOWS FOR FINE GRAINED COMMANDS AND REUSE
- 45. Caching • Introduce cacheable interface • simple marker interface, • or more elaborate version with cache id, expiration time, etc… • Implement caching (client or server side)
- 46. Patient 1! Patient 1 details ! Patient 2 0101010101010101001010101010101010101010101010101! 0101010101010101001010101010101010101010101010101! 0101010101010101001010101010101010101010101010101! 0101010101010101001010101010101010101010101010101! 0101010101010101001010101010101010101010101010101! 0101010101010101001010101010101010101010101010101! 0101010101010101001010101010101010101010101010101! 0101010101010101001010101010101010101010101010101
- 47. action 1 action 2 execution 1 execution 2 result 2 result 1 Ops.
- 48. Ensure „only last“ result action 1 action 2 „smart dispatch“ action 1 handler last action is: action result 2 result 1 result 1 check result deliver if last! result
- 49. Re-Auth • If server exception is security exception, try to reauth and than re-execute commands
- 50. ‣ Client-Server communication ‣ Command pattern ‣ Versioning ‣ Batching, Caching ‣ Scaling
- 51. GWT scaling is easy... • Every client brings his own CPU power • The client does the page rendering • GWT provides different ways to reduce number of requests even more • The server must „only“ authenticate the user and provide the data, perform the actions requested by the client
- 52. WHAT CAN POSSIBLY GO WRONG?
- 53. LETS TALK HIGH TRAFFIC... HIGH TRAFFIC IS WHEN ONE SERVER IS NOT ENOUGH
- 54. HIGH TRAFFIC PROBLEMS • Bandwith issues • Connection pool bottlenecks • Thread pool bottlenecks • CPU bottlenecks caused by reflection API calls • High JVM garbage collection CPU usage
- 55. NOT REALLY GWT PROBLEMS, BUT WHAT CAN WE DO?
- 56. avoid „tx collisions“ TX TX TX TX TX TX TX TX TX 5 gleichzeitige Transaktionen
- 57. load small portions of data, do it often TX TX TX TX TX TX TX TX TX TX TX TX TX TX TX
- 59. IMPLEMENT REAL LOAD BALANCING EACH REQUEST GOES TO THE NEXT AVAILABLE SERVER
- 60. SCALING HOW-TO • Don‘t stick a session to a server. Why send a user over and over again to a possible overloaded server? • Don‘t store anything on the HTTP session. Share session content outside web container • Session replication is expensive and does not scale well • Let the load balancer distribute calls to available servers
- 62. Session state could contain user id, client id, session id, user roles Session Cache If session cache becomes bottleneck, use distributed cache Session Cache Session Cache
- 63. Thanks!