JSF Locale exception

Question

I'm new to JSF and I would like to internationalize my web page so the web site visitor would be able to switch between languages by clicking on flag icons representing each locale. I have edited my faces-config.xml and added resource bundle, default locale, and supported locales. Then I wrote a bean called changeLang.java which is supposed to be for doing the background job. When the page is evaulated I get the following error:

index.xhtml @8,89 locale="#{changeLang.currentLocale}" Attribute did not evaluate to a String or Locale: null

Technologies:
JSF 2.0 Mojarra 2.0.2
Spring 3.0.0
Facelets

My
changeLang.java file

package gui;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Locale;
import javax.annotation.ManagedBean;
import javax.faces.context.FacesContext;
import org.springframework.context.annotation.Scope;

@ManagedBean
@Scope("session")

public class ChangeLang {
    private Locale currentLocale;

    public ChangeLang() {
           this.currentLocale = FacesContext.getCurrentInstance().getApplication().getDefaultLocale();
    }
    public Locale getCurrentLocale() {
        return this.currentLocale;
    }
    public ArrayList getSupportedLocales(){
        ArrayList listOfSupp = new ArrayList();
        Iterator locales = FacesContext.getCurrentInstance().getApplication().getSupportedLocales();
        while(locales.hasNext()) {
            Locale locale = locales.next();
            listOfSupp.add(locale);
        }

    return listOfSupp;
    }
    public void setCurrentLocaleLanguage(String language) {
        FacesContext.getCurrentInstance().getViewRoot().setLocale(new Locale(language));
    }
}

and "using page" snippet

 
f:view locale="#{changeLang.currentLocale}" contentType="text/html; charset=utf-8"

Full log:

An Error Occurred:
/index.xhtml @8,89 locale="#{changeLang.currentLocale}" Attribute did not evaluate to a String or Locale: null
- Stack Trace
javax.faces.view.facelets.TagAttributeException: /index.xhtml @8,89 locale="#{changeLang.currentLocale}" Attribute did not evaluate to a String or Locale: null
    at com.sun.faces.facelets.tag.jsf.ComponentSupport.getLocale(ComponentSupport.java:218)
    at com.sun.faces.facelets.tag.jsf.core.ViewHandler.apply(ViewHandler.java:119)
    at com.sun.faces.facelets.tag.ui.CompositionHandler.apply(CompositionHandler.java:160)
    at com.sun.faces.facelets.compiler.NamespaceHandler.apply(NamespaceHandler.java:86)
    at com.sun.faces.facelets.compiler.EncodingHandler.apply(EncodingHandler.java:75)
    at com.sun.faces.facelets.impl.DefaultFacelet.apply(DefaultFacelet.java:145)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.buildView(FaceletViewHandlingStrategy.java:716)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:106)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:313)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1523)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97)
    at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:332)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:233)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:693)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:954)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:170)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:69)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309)
    at java.lang.Thread.run(Thread.java:619)
- Component Tree

- Scoped Variables
Request ParametersName  Value
None

View AttributesName Value
None

Request AttributesName  Value
None

Flash AttributesName    Value
None

Session AttributesName  Value
None

Application AttributesName  Value
csfcff  com.sun.faces.context.flash.ELFlash@119f705d

Please, would you be so kind and help me to solve this problem ?

Thanks for any advice.

  <locale-config>
        <default-locale>en</default-locale>
        <supported-locale>en</supported-locale>
        <supported-locale>sk</supported-locale>
        <supported-locale>ko</supported-locale>
    </locale-config>

Answer 1

Well, you need to set the default value. Either

Locale currentLocale = FacesContext.getCurrentContext()
           .getApplication().getDefaultLocale();

or

@PostConstruct
public void init() {
    currentLocale = FacesContext.getCurrentContext()
           .getApplication().getDefaultLocale();
}

Answer 2

The error says that the Locale is null while it may not be null. You need to preinitialize it with ExternalContext#getRequestLocale() which will return the client side locale, not with the Application#getDefaultLocale() which would return the server side locale which may be null if not explicitly configured.

So, update your code with

public changeLang() {
    this.currentLocale = FacesContext.getCurrentInstance().getExternalContext().getRequestLocale();
}

That said, it's recommend to adhere the Sun Java Naming Conventions . Classnames ought to start with uppercase, else it would confuse everyone because it look like methods. Rename changeLang to ChangeLang .