如何使用应用程序作用域bean初始化DB？

Question

以下bean代码来自example project belonging to a book on JSF。练习是为了解决以下问题：
当您在第二个浏览器中打开项目时，init()将再次执行，因为bean是会话范围的，因此将创建重复的DB条目。 提示是使用应用程序作用域bean将数据初始化为DB 我找到了this question，但我无法解决这个问题。如果我使用@ManagedBean(eager=true)，则JSF-Page将保持为空，并且数据库似乎不会被初始化。

package hoho;

import java.io.Serializable;
import java.util.GregorianCalendar;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.annotation.PostConstruct;
import javax.annotation.Resource;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.faces.model.DataModel;
import javax.faces.model.ListDataModel;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.transaction.UserTransaction;

@ManagedBean
@SessionScoped
public class ComedianHandler implements Serializable {

    @PersistenceContext
    private EntityManager em;

    @Resource
    private UserTransaction utx;


    private DataModel<Comedian> comedians;
    private Comedian currentComedian = new Comedian();

    public ComedianHandler() {
        Logger.getAnonymousLogger().log(Level.INFO, "Constructor ComedianHandler() called");    
    }

    /*
     * Known mistake: method is called per session, i.e. data will be
     * written into DB for EACH session
     * possible fix: put into application scoped bean
     */
    @PostConstruct
    public void init() {
        Logger.getAnonymousLogger().log(Level.INFO, "'init()' called");
        try {
            utx.begin();
            em.persist(new Comedian("Mario", "Barth", new GregorianCalendar(1972, 10, 1).getTime()));
            em.persist(new Comedian("Atze", "Schröder", new GregorianCalendar(1965, 8, 27).getTime()));
            em.persist(new Comedian("Dieter", "Nuhr", new GregorianCalendar(1960, 9, 29).getTime()));
            em.persist(new Comedian("Anke", "Engelke", new GregorianCalendar(1965, 11, 21).getTime()));
            em.persist(new Comedian("Kaya", "Yanar", new GregorianCalendar(1973, 4, 20).getTime()));
            comedians = new ListDataModel<Comedian>();
            comedians.setWrappedData(em.createNamedQuery("SelectComedians").getResultList());
            utx.comwith();          
        } catch (Exception e) {
            Logger.getAnonymousLogger().log(Level.SEVERE, "'init()' did not work", e.getMessage());
        }
    }

    public String save() {
        Logger.getAnonymousLogger().log(Level.INFO, "save() [1] with " + currentComedian +  "' called");
        try {
            utx.begin();
            currentComedian = em.merge(currentComedian);
            Logger.getAnonymousLogger().log(Level.INFO, "save() [2] with " + currentComedian+  "' called");
            em.persist(currentComedian);
            comedians.setWrappedData(em.createNamedQuery("SelectComedians").getResultList());
            utx.comwith();
        } catch (Exception e) {
            Logger.getAnonymousLogger().log(Level.SEVERE, "'save()' did not work", e.getMessage());
        }
        return "/display-comedians.xhtml";
    }


    public String change() {
        currentComedian = comedians.getRowData();
        Logger.getAnonymousLogger().log(Level.INFO, "change() with " + currentComedian);
        return "/comedian.xhtml";
    }

    public String newEntry() {
        currentComedian = new Comedian();
        Logger.getAnonymousLogger().log(Level.INFO, "newEntry()");
        return "/comedian.xhtml";
    }

    public String delete() {
        currentComedian = comedians.getRowData();
        Logger.getAnonymousLogger().log(Level.INFO, "delete() with " + currentComedian);
        try {
            utx.begin();
            currentComedian = em.merge(currentComedian);
            em.remove(currentComedian);
            comedians.setWrappedData(em.createNamedQuery("SelectComedians").getResultList());
            utx.comwith();
        } catch (Exception e) {
            Logger.getAnonymousLogger().log(Level.SEVERE, "'delete()' did not work", e.getMessage());
        }
        return null;
    }

    public DataModel<Comedian> getComedians() {
        return comedians;
    }


    public Comedian getCurrentComedian() {
        return currentComedian;
    }
    public void setCurrentComedian(Comedian currentComedian) {
        this.currentComedian = currentComedian;
    }


}

facelets代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" 
      xmlns:h="http://java.sun.com/jsf/html" 
      xmlns:f="http://java.sun.com/jsf/core">

<head>
    <title>Display Comedians</title>
    <link rel="stylesheet" href="style.css" type="text/css" />
</head>

<body>
    <h:form>
        <h:dataTable value="#{comedianHandler.comedians}" var="comedian"
                rowClasses="odd,even" headerClass="header" footerClass="footer">
            <f:facet name="header">Display all Comedians</f:facet>
            <f:facet name="footer">#{resourceBundle.copyright}</f:facet>
            <h:column>
                <f:facet name="header">First Name</f:facet>
                #{comedian.firstName}
            </h:column>
            <h:column>
                <f:facet name="header">Last Name</f:facet>
                #{comedian.lastname}
            </h:column>
            <h:column>
                <f:facet name="header">Day of Birth</f:facet>
                <h:outputText value="#{comedian.dayOfBirth}">
                    <f:convertDateTime pattern="dd.MM.yyyy"/>
                </h:outputText>
            </h:column>
            <h:column>
                <h:commandButton action="#{comedianHandler.change}" value="Change" />
            </h:column>
            <h:column>
                <h:commandButton action="#{comedianHandler.delete}" value="Delete" />
            </h:column>
        </h:dataTable>
        <h:commandButton action="#{comedianHandler.newEntry}" value="new Entry" style="width: 80px; margin: 10px 2px 2px 2px;" />
    </h:form>
</body>

</html>