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Java EE Pattern: The Control Layer

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Java EE Patterns related to the Control Layer, thanks to the inspiring book from Adam Bien, part of the lectures held at Duale Hochschule Mannheim

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Java EE Pattern: The Control Layer

  1. 1. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 1 Session: Pattern of the Control Layer Singleton Service Starter Simple Workflows
  2. 2. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 2 Objectives Learn about: ✔ How to start a service at deploy time ✔ Dealing with timers ✔ The Singleton pattern in Java EE ✔ The State Pattern in conjunction with simple workflows
  3. 3. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 3 Some orientation Consumer Consumer Layer Integration Layer Business Process Layer Services Layer Component Layer OS Layer
  4. 4. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 4 ECB Pattern Entity Control Boundary ✔ Based upon Robustness Diagrams (http://www.agilemodeling.com/artifacts/robustnessDiagram.htm) ➢ Boundary: user interface ➢ Control: actual process or activity ➢ Entity: a concept from an enterprise context. ✔ Elements are generic enough to be mapped either to service- oriented or object-oriented architectures. Boundary Control Entity Adam Bien
  5. 5. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 5 Services, components and patterns Boundary Control Entity DAO & Domain Store Generic DAO Singleton Service Starter Dual View SOA Facade Lightweight asynchronous Facade Multichannel Facade TO & DTO Paginator Bean Locator Multichannel Facade Resource Binder Payload Extractor Aynchronous Resource Integrator Infrastructure
  6. 6. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 6 Module Singleton
  7. 7. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 7 Singleton ✔ Access to limited resources needs to be shared across user requests. ✔ Amount of active SLSB is dependent on: ➢ Parallel user requests ➢ Pool settings (min/max) ➢ Both isn't covered by spec. ✔ The solution should be portable between app.-servers.
  8. 8. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 8 Singleton ✔ Most effective in terms of caches, application-wide configuration parameters or cyclic actions. ✔ Often combined with Service Starter (therefore we'll combine both labs) @Singleton(mappedName = "ejb/facade/ServiceStarter") @Remote(ServiceStarter.class) public class ServiceStarterBean implements ServiceStarter { ...
  9. 9. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 9 Module Service Starter
  10. 10. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 10 Service Starter ✔ Some logic needs to be initialized prior to the business logic ✔ Some services might depend on each other ✔ Since EJB 3.1 these initializations are specified, in EJB 3.0 they were not. ➢ In EJB 3.1: @Startup combined with @PostConstruct ➢ In EJB 3.0: Servlet and <load-on-startup> plus CDI
  11. 11. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 11 Example Think of the following: ✔ Some production data needs to be retrieved for further processing ✔ You have to integrate a 3rd party system by means of cyclic, synchronous calls. ✔ Maybe you want to make use of timers, be aware, you can create timers from MDBs or Singletons only.
  12. 12. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 12 Example ✔ ServiceStarterBean @Singleton(mappedName = "ejb/facade/ServiceStarter") @Startup @Remote(ServiceStarter.class) public class ServiceStarterBean implements ServiceStarter { private Logger log = Logger.getLogger(ServiceStarterBean.class); @EJB private PollingServiceBean pollingService; /** the timer service */ @Resource private javax.ejb.TimerService timerService; @PostConstruct public void init(){ log.info("initializing"); } ...
  13. 13. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 13 Example ✔ ServiceStarterBean (cont.) @Schedule(second = "*/5", minute="*", hour="*", persistent = false, info="Timer: external polling") public void notifyPollingService(){ this.pollingService.doPoll(); } public void stopTimer(String timerName){ Collection<Timer> timers = this.timerService.getTimers(); for (Timer timer : timers){ if(timer.getInfo().toString().equals(timerName)){ timer.cancel(); log.info("Timer: " + timerName + " has been cancelled"); } }
  14. 14. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 14 Example ✔ External configuration: ejb-jar.xml (overwrites the annotation) <?xml version="1.0" encoding="UTF-8"?> <ejb-jar xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb- jar_3_1.xsd" version="3.1"> <display-name>Pattern Training</display-name> <enterprise-beans> <session> <ejb-name>ServiceStarterBean</ejb-name> <ejb-class>de.brockhaus.userMgmt.control.ServiceStarterBean</ejb-class> <timer> <description>none</description> <schedule> <second>0/5</second> <minute>*</minute> <hour>*</hour> </schedule> <timeout-method> <method-name>notifyPollingService</method-name> </timeout-method> <persistent>false</persistent> <info>Timer: external polling</info> </timer> </session> </enterprise-beans> </ejb-jar>
  15. 15. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 15 Lab Implement Service Activator (not more than 15 min.)
  16. 16. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 16 Module Simple Workflows
  17. 17. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 17 Simple Workflow ✔ Within the control layer, it might happen, you have to perform several (identical) steps within different services / methods: ➢ Checking for existence of x, maybe in system y ➢ Calculating amounts of a, b, c (e.g. in a production plan for a certain period) ➢ ... ✔ You might end up in the idea of decomposition into processes and activities ➢ Has only little to do with Java EE ➢ Inspired by State Machines and Workflow Engines ➢ No maintenance of state of a current workflow instance
  18. 18. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 18 The abstract process An abstract superclass providing methods to: ✔ Proceed (starting the process) ✔ Initialize the process ✔ Finalize the process
  19. 19. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 19 The abstract process public abstract class Process{ private Logger log = Logger.getLogger(Process.class); public static final int PROCESS_START = 1; public static final int PROCESS_END = 999; private int runstate = 1; private boolean hasFinished = false; public synchronized void proceed() throws ProcessException{ try{ this.beforeProcess(); while (runstate != Process.PROCESS_END){ runSteps(); } this.afterProcess(); this.end(); } catch (ProcessException e) { ... } catch (Exception e){ ... } } ...
  20. 20. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 20 The activity ✔ Common interface to all process related activities: public interface ProcessActivity { public <T> T proceedActivity<T>(); }
  21. 21. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 21 The activity ✔ Concrete activity (example) ➢ Make use of the constructor to pass parameters ➢ Return whatever you want from processActivity public class StepOne implements ProcessActivity { private Logger log = Logger.getLogger(this.getClass()); private int value; public StepOne(int value){ this.value = value; } public <T> T proceedActivity(){ log.info(this.getClass().getSimpleName() + " invoked"); if(this.value > 99){ return (T) new Boolean(true); } else { return (T) new Boolean(false); } } }
  22. 22. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 22 A concrete process ✔ Extend Process and overwrite runSteps() according to the activities public class SomeProcess extends de.brockhaus.userMgmt.util.Process { private int amount; public SomeProcess(int amount) { this.amount = amount; } @Override public void runSteps() throws ProcessException { switch(super.getRunstate()) { case(1): this.triggerStepOne(); break; case(2): this.triggerStepTwo(); break; case(3): this.triggerStepThree(); break; default: super.setRunstate(PROCESS_END); } }
  23. 23. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 23 A concrete process ✔ Decide upon the activities outcome what needs to be done next private void triggerStepOne(){ StepOne one = new StepOne(amount); boolean ret = one.proceedActivity(); if(ret){ super.setRunstate(2); } else{ super.setRunstate(3); } } private void triggerStepTwo() { StepTwo two = new StepTwo(); two.proceedActivity(); super.setRunstate(PROCESS_END); } private void triggerStepThree() { StepThree three = new StepThree(); three.proceedActivity(); super.setRunstate(PROCESS_END); }
  24. 24. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 24 Relation to the control layer ✔ Obviously the process has to be connected to the SLSBs of the control layer @Stateless @Remote(SomeService.class) public class SomeServiceBean implements SomeService { // inject SomeProcess @Inject private SomeProcess p; public void someBusinessMethod(int amount) throws ProcessException { // set amount at process p.setAmount(amount); // proceed process p.proceed(); } }
  25. 25. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 25 Some conclusion Pros ✔ It's pretty simple and effective ✔ Well designed it might help a lot to stay with DRY paradigm ✔ Provides flexibility, just exchange an activity within a process and the process will behave different. Cons ✔ Don't think of too many activities, don't think of fully fledged workflows spanning several components / modules ✔ No graphical support, no modelling
  26. 26. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 26 Lab Implement Simple Workflows (State Machine) (not more than 15 min.)
  27. 27. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 27 Review Session Review: ✔ @PostConstruct, what is this good for? ✔ Can you provide some examples of using Singletons in Java EE? ✔ Why do we have processes and services in the example and what makes the difference to workflow engines?
  28. 28. Copyright by Brockhaus GmbH, alle Rechte reserviert, unautorisierte Vervielfältigung untersagt 28 Recommeded reading ✔ http://java.sun.com/blueprints/corej2eepatterns/ ✔ http://www.corej2eepatterns.com/Patterns2ndEd/ ✔ Adam Bien, J2EE Patterns, Addison Wesley 2002, ISBN: 3-8273-1903-X ✔ Floyd Marinescu, Ed Roman: Ejb Design Patterns: Advanced Patterns, Processes, and Idioms; Wiley & Sons, ISBN-10: 0471208310 ✔ And other ... Photo: Bundesarchiv

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