This document discusses several common anti-patterns in JavaServer Faces (JSF) development and provides solutions to avoid them. It covers issues like validating setters, dependency injection, thread safety, vendor lock-in, the Law of Demeter principle, and database performance problems like N+1 queries. The document is written by Dennis Byrne and provides best practices for building scalable and maintainable JSF applications.

1. JavaServer Faces Anti-Patterns Dennis Byrne - ThoughtWorks [email_address] http://notdennisbyrne.blogspot.com

2. Validating Setter <managed-bean> <managed-bean-name>iterationBean</managed-bean-name> <managed-bean-class> com.thoughtworks.Iteration </managed-bean-class> <managed-bean-scope> request </managed-bean-scope> <managed-property> <property-name> start </property-name> <value> #{sprintBean.currentStart} </value> </managed-property> <managed-property> <property-name> end </property-name> <value> #{sprintBean.currentEnd} </value> </managed-property> <managed-property> <property-name>last</property-name> <value>hack</value> </managed-property> </managed-bean>

3. Validating Setter public class Iteration { private Calendar start, end; // injected // sans setters and getters for start, end public void setLast(String last) { if(start == null) throw new NullPointerException(&quot;start&quot;); if(end == null) throw new NullPointerException(&quot;end&quot;); if(start.after(end)) throw new IllegalStateException(&quot;start > end&quot;); } }

4. Validating Setter Solutions <application> <variable-resolver> org.springframework.web.jsf.DelegatingVariableResolver </variable-resolver> </application> <application> <el-resolver> org.apache.myfaces.el.unified.resolver.GuiceResolver </el-resolver> </application> public class Iteration { private Calendar start, end; // injected @PostConstruct public void initialize() { // domain validation logic here ... } }

5. The Map Trick #{requestScopedMap.key} // calls get(‘key’) #{requestScopedMap[‘key’]} public class MapTrick implements java.util.Map { public Object get(Object key) { return new BusinessLogic().doSomething(key); } public void clear() { } public boolean containsKey(Object arg) { return false; } public boolean isEmpty() { return false; } public Set keySet() { return null; } public Object put(Object key, Object value) { return null; } public void putAll(Map arg) { } public Object remove(Object arg) { return null; } public int size() { return 0; } }

6. déjà vu PhaseListener <context-param> <description> comma separated list of JSF conf files </description> <param-name> javax.faces.CONFIG_FILES </param-name> <param-value> /WEB-INF/faces-config.xml </param-value> </context-param> <lifecycle> <phase-listener> com.thoughtworks.PhaseListenerImpl </phase-listener> </lifecycle>

7. XML Hell <navigation-rule> <from-view-id>/home.xhtml</from-view-id> <navigation-case> <from-outcome>contact_us</from-outcome> <to-view-id>/contact.xhtml</to-view-id> </navigation-case> </navigation-rule> <navigation-rule> <from-view-id>/site_map.xhtml</from-view-id> <navigation-case> <from-outcome>contact_us</from-outcome> <to-view-id>/contact.xhtml</to-view-id> </navigation-case> </navigation-rule> <navigation-rule><from-view-id> * </from-view-id> <navigation-case> <!-- global nav rule --> <from-outcome>contact_us</from-outcome> <to-view-id>/contact.xhtml</to-view-id> </navigation-case> </navigation-rule>

8. Thread Safety javax.faces.event.PhaseListener javax.faces.render.Renderer Managed Beans javax.faces.convert.Converter javax.faces.validator.Validator javax.faces.FacesContext JSF Tags

9. Thread Safety <h:inputText value=&quot;#{managedBean.value}&quot; converter=&quot;#{threadUnsafe}&quot; /> <managed-bean> <managed-bean-name>threadUnsafe</managed-bean-name> <managed-bean-class> org.apache.myfaces.book.ThreadUnsafeConverter </managed-bean-class> <managed-bean-scope> session </managed-bean-scope> </managed-bean> <h:inputText value=&quot;#{managedBean.value}&quot; > <f:converter converterId=&quot;threadUnsafe&quot; > <!-- Always Safe --> </h:inputText> <converter> <converter-id>threadUnsafe</converter-id> <converter-class>org.apache.myfaces.book.ThreadUnsafeConverter </converter-class> </converter>

10. Facelets Migration public class WidgetTag extends UIComponentELTag{ private String title, styleClass = &quot;default_class&quot;; protected void setProperties(UIComponent component) { super.setProperties(component); Widget span = (Widget) component; span.setStyleClass(styleClass); span.setTitle(title == null ? &quot;no title&quot; : title); FacesContext ctx = FacesContext.getCurrentInstance(); Map session = ctx.getExternalContext().getSessionMap(); span.setStyle((String) session.get(&quot;style&quot;)); } }

11. Law of Demeter A “Train Wreck” - sensitive to changes in domain model employee. getDepartment().getManager() .getOffice().getAddress().getZip(); An EL “Train Wreck” - sensitive to changes in domain model #{employee. department.manager.office.address.zip } Encapsulated, insensitive to changes in domain model #{employee.officeManagersZipCode}

12. Vendor Lock-in import org.apache.myfaces.component.html.ext.HtmlInputHidden; import org.apache.myfaces.component.html.ext.HtmlInputText; import org.apache.myfaces.component.html.ext.HtmlOutputText; public class ImplementationDependentManagedBean { private HtmlInputText input ; private HtmlInputHidden hidden ; private HtmlOutputText output ; /* getters and setters omitted */ public boolean recordTotal(ActionEvent event) { long total = ((Long)input.getValue()).longValue(); total += ((Long)hidden.getValue()).longValue(); total += ((Long)output.getValue()).longValue(); return new JmsUtil().broadcastTotal(total); } }

13. Vendor Lock-in Solution import javax.faces.component.ValueHolder; public class RefactoredManagedBean { private ValueHolder input ; private ValueHolder hidden ; private ValueHolder output ; /* getters & setters ommitted */ public boolean recordTotal(ActionEvent event) { long total = 0; ValueHolder[] vh = new ValueHolder[] {input, hidden, output}; for(ValueHolder valued : vh) total += ((Long)valued.getValue()).longValue(); return new JmsUtil().broadcastTotal(total); } }

14. Portlet ClassCastException FacesContext ctx = FacesContext.getCurrentInstance(); ExternalContext ectx = ctx.getExternalContext(); ServletRequest request = ( ServletRequest )ectx .getRequest(); String id = request.getParameter(&quot;id&quot;); FacesContext ctx = FacesContext.getCurrentInstance(); ExternalContext ectx = ctx.getExternalContext(); String id = ectx.getRequestParameterMap().get(&quot;id&quot;);

15. OpenTransactionInViewFilter public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain){ try { ObjectRelationalUtility.startTransaction(); chain.doFilter(request, response); ObjectRelationalUtility.commitTransaction(); } catch (Throwable throwable) { try { ObjectRelationalUtility.rollbackTransaction(); } catch (Throwable _throwable) { /* sans error handling */ } } }

16. N + 1 <!-- One trip to the database for the master record ... --> <h:dataTable value=&quot;#{projectBean.projects}&quot; var=&quot;project&quot;> <h:column> <h:commandLink action=&quot;#{projectBean.viewProject}&quot; value=&quot;view project&quot;/> </h:column> <h:column> <!-- ... and + N trips for each child record --> <f:facet name=&quot;header&quot;>Project Manager</f:facet> #{project .manager.name } </h:column> <h:column> <f:facet name=&quot;header&quot;>Project Name</f:facet> #{project.name} </h:column> </h:dataTable>

17. N + 1- N public class OpenTransactionInApplicationPhaseListener implements PhaseListener { public void beforePhase(PhaseEvent event) { try { ObjectRelationalUtility.startTransaction(); } catch (Throwable throwable) { /* sans error handling */ } } public void afterPhase(PhaseEvent event) { try { ObjectRelationalUtility.commitTransaction(); } catch (Throwable throwable) { ObjectRelationalUtility.rollbackTransaction(); } } public PhaseId getPhaseId(){return PhaseId.INVOKE_APPLICATION ;} }

18. Thanks Dennis Byrne - ThoughtWorks [email_address] http://notdennisbyrne.blogspot.com