JavaServer Faces Anti-Patterns

1
JavaServer Faces Anti-Patterns

• Dennis Byrne - ThoughtWorks
• dennisbyrne_at_apache.org

2
Validating Setter

• ltmanaged-beangt
• ltmanaged-bean-namegtiterationBeanlt/managed-be
  an-namegt
• ltmanaged-bean-classgtcom.thoughtworks.Iterati
  on
• lt/managed-bean-classgt
• ltmanaged-bean-scopegtrequestlt/managed-bean-sc
  opegt
• ltmanaged-propertygt
• ltproperty-namegtstartlt/property-namegt
• ltvaluegtsprintBean.currentStartlt/valuegt
• lt/managed-propertygt
• ltmanaged-propertygt
• ltproperty-namegtendlt/property-namegt
• ltvaluegtsprintBean.currentEndlt/valuegt
• lt/managed-propertygt
• ltmanaged-propertygt
• ltproperty-namegtlastlt/property-namegt
• ltvaluegthacklt/valuegt
• lt/managed-propertygt
• lt/managed-beangt

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("start")
• if(end null)
• throw new NullPointerException("end")
• if(start.after(end))
• throw new IllegalStateException("start gt
  end")

4
Validating Setter Solutions

• ltapplicationgt
• ltvariable-resolvergt
• org.springframework.web.jsf.DelegatingVariableRe
  solver
• lt/variable-resolvergt
• lt/applicationgt
• ltapplicationgtltel-resolvergt
• org.apache.myfaces.el.unified.resolver.GuiceReso
  lver
• lt/el-resolvergt
• lt/applicationgt
• public class Iteration
• private Calendar start, end // injected
• _at_PostConstruct
• public void initialize()
• // domain validation logic here ...

5
The Map Trick

• requestScopedMap.key // calls
  get(key)
• requestScopedMapkey
• 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

• ltcontext-paramgt
• ltdescriptiongt
• comma separated list of JSF conf files
• lt/descriptiongt
• ltparam-namegtjavax.faces.CONFIG_FILESlt/param-na
  megt
• ltparam-valuegt
• /WEB-INF/faces-config.xml
• lt/param-valuegt
• lt/context-paramgt
• ltlifecyclegt
• ltphase-listenergt
• com.thoughtworks.PhaseListenerImpl
• lt/phase-listenergt
• lt/lifecyclegt

7
XML Hell

• ltnavigation-rulegtltfrom-view-idgt/home.xhtmllt/from-v
  iew-idgt
• ltnavigation-casegt
• ltfrom-outcomegtcontact_uslt/from-outcomegt
• ltto-view-idgt/contact.xhtmllt/to-view-idgt
• lt/navigation-casegt
• lt/navigation-rulegt
• ltnavigation-rulegtltfrom-view-idgt/site_map.xhtmllt/fr
  om-view-idgt
• ltnavigation-casegt
• ltfrom-outcomegtcontact_uslt/from-outcomegt
• ltto-view-idgt/contact.xhtmllt/to-view-idgt
• lt/navigation-casegt
• lt/navigation-rulegt
• ltnavigation-rulegtltfrom-view-idgtlt/from-view-idgt
• ltnavigation-casegt lt!-- global nav rule --gt
• ltfrom-outcomegtcontact_uslt/from-outcomegt
• ltto-view-idgt/contact.xhtmllt/to-view-idgt
• lt/navigation-casegt
• lt/navigation-rulegt

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

• lthinputText value"managedBean.value"
  converter"threadUnsafe" /gt
• ltmanaged-beangt
• ltmanaged-bean-namegtthreadUnsafelt/managed-
  bean-namegt
• ltmanaged-bean-classgt
• org.apache.myfaces.book.ThreadUnsafeConverter
• lt/managed-bean-classgt
• ltmanaged-bean-scopegtsessionlt/managed-bean
  -scopegt
• lt/managed-beangt
• lthinputText value"managedBean.value" gt
• ltfconverter converterId"threadUnsafe" gt
  lt!-- Always Safe --gt
• lt/hinputTextgt
• ltconvertergt
• ltconverter-idgtthreadUnsafelt/converter-idgt
• ltconverter-classgtorg.apache.myfaces.book.T
  hreadUnsafeConverter
• lt/converter-classgt
• lt/convertergt

10
Facelets Migration

• public class WidgetTag extends UIComponentELTag
• private String title, styleClass
  "default_class"
• protected void setProperties(UIComponent
  component)
• super.setProperties(component)
• Widget span (Widget) component
• span.setStyleClass(styleClass)
• span.setTitle(title null ? "no title"
  title)
• FacesContext ctx FacesContext.getCurrentInstan
  ce()
• Map session ctx.getExternalContext().getSessio
  nMap()
• span.setStyle((String) session.get("style"))

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.HtmlI
  nputHidden
• import org.apache.myfaces.component.html.ext.HtmlI
  nputText
• import org.apache.myfaces.component.html.ext.HtmlO
  utputText
• 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()).longV
  alue()
• total ((Long)hidden.getValue()).longValu
  e()
• total ((Long)output.getValue()).longValu
  e()
• 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()).long
  Value()
• 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("id")
• FacesContext ctx FacesContext.getCurrentInstance
  ()
• ExternalContext ectx ctx.getExternalContext()
• String id ectx.getRequestParameterMap().get("id"
  )

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

• lt!-- One trip to the database for the master
  record ... --gt
• lthdataTable value"projectBean.projects"
  var"project"gt
• lthcolumngt
• lthcommandLink action"projectBean.viewProj
  ect"
• value"view project"/gt
• lt/hcolumngt
• lthcolumngt
• lt!-- ... and N trips for each child record
  --gt
• ltffacet name"header"gtProject
  Managerlt/ffacetgt
• project.manager.name
• lt/hcolumngt
• lthcolumngt
• ltffacet name"header"gtProject
  Namelt/ffacetgt
• project.name
• lt/hcolumngt
• lt/hdataTablegt

17
N 1- N

• public class OpenTransactionInApplicationPhaseList
  ener
• implements PhaseListener
• public void afterPhase(PhaseEvent event)
• try
• ObjectRelationalUtility.startTransaction()
• catch (Throwable throwable) / sans error
  handling /
• public void beforePhase(PhaseEvent event)
• try
• ObjectRelationalUtility.commitTransaction()
• catch (Throwable throwable)
• ObjectRelationalUtility.rollbackTransaction()
• public PhaseId getPhaseId()return
  PhaseId.INVOKE_APPLICATION