Ошибка с TreeNode (Primefaces)

Question

Я разрабатываю систему с использованием jsf, hibernate, spring и primefaces. У меня есть один объект, который в каждой вставке, все данные представлены в TreeNode. Когда я выбираю один узел из дерева, должна появиться форма, чтобы я мог редактировать выбранный элемент. Да, это работает очень хорошо. Но есть ошибка, когда я щелкаю один раз в узле, который появляется в консоли. Если я дважды нажму, это работает. Но я хочу знать, что это за ошибка, которая появляется, когда я щелкаю один раз в узле.

Посмотрите:

Jul 19, 2013 9:37:05 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
    at org.primefaces.component.tree.Tree.processUpdates(Tree.java:308)
    at javax.faces.component.UIComponentBase.processUpdates(UIComponentBase.java:1289)
    at javax.faces.component.UIViewRoot.processUpdates(UIViewRoot.java:1254)
    at com.sun.faces.lifecycle.UpdateModelValuesPhase.execute(UpdateModelValuesPhase.java:78)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:344)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:110)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:98)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:95)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:79)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:120)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:55)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:36)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:188)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:106)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:80)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:150)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at financeiro.web.filter.ConexaoHibernateFilter.doFilter(ConexaoHibernateFilter.java:24)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:724)

Jul 19, 2013 9:39:06 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
    at org.primefaces.component.tree.Tree.processUpdates(Tree.java:308)
    at javax.faces.component.UIComponentBase.processUpdates(UIComponentBase.java:1289)
    at javax.faces.component.UIViewRoot.processUpdates(UIViewRoot.java:1254)
    at com.sun.faces.lifecycle.UpdateModelValuesPhase.execute(UpdateModelValuesPhase.java:78)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:344)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:110)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:98)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:95)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:79)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:120)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:55)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:36)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:188)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:106)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:80)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:356)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:150)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at financeiro.web.filter.ConexaoHibernateFilter.doFilter(ConexaoHibernateFilter.java:24)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:724)

Вот страница HTML:

<?xml version="1.0" encoding="ISO-8859-1"?>
<!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"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:p="http://primefaces.prime.com.tr/ui">

<ui:composition template="/templates/interna.xhtml">
    <ui:define name="titulo">
        Categorias
    </ui:define>

    <ui:define name="corpo">
        <f:view contentType="text/html">
            <h:panelGrid columns="2" cellpadding="5">
                <h:panelGroup>
                    <h:form>
                        <p:commandButton value="Novo" action="#{categoriaBean.novo}" update="edicao" />
                    </h:form>
                    <br />
                    <h:form id="arvore">
                        <p:tree value="#{categoriaBean.categoriasTree}" var="node"
                            dynamic="false" 
                            selectionMode="single"
                            nodeSelectListener="#{categoriaBean.selecionar}"
                            update="edicao"
                            expandAnim="FADE_IN" collapseAnim="FADE_OUT">
                            <p:treeNode>
                                <h:outputText value="#{node.descricao}" />
                            </p:treeNode>
                        </p:tree>
                    </h:form>
                </h:panelGroup>

                <h:panelGroup id="edicao">
                    <h:messages />
                    <h:form rendered="#{categoriaBean.mostraEdicao}">
                        <h:inputHidden value="#{categoriaBean.editada.codigo}" />
                        <h:inputHidden value="#{categoriaBean.editada.fator}" />
                        <h:panelGrid columns="2">
                            <h:outputLabel value="Pai" />
                            <h:selectOneMenu value="#{categoriaBean.editada.pai}">
                                <f:selectItems value="#{categoriaBean.categoriasSelect}" />
                            </h:selectOneMenu>
                            <h:outputLabel value="Descrição" />
                            <h:inputText value="#{categoriaBean.editada.descricao}" />
                            <h:outputText />
                            <h:panelGroup>
                                <p:commandButton value="Salvar" action="#{categoriaBean.salvar}" 
                                    update="edicao, arvore" />
                                <p:commandButton value="Excluir" action="#{categoriaBean.excluir}" 
                                    update="edicao, arvore" />
                            </h:panelGroup>
                            <h:outputText />
                            <p:commandButton value="Nova subcategoria" action="#{categoriaBean.novo}" 
                                update="edicao" />
                        </h:panelGrid>
                    </h:form>
                </h:panelGroup>
            </h:panelGrid>
        </f:view>
    </ui:define>
</ui:composition>

</html>

Вот класс Бин:

@ManagedBean(name = "categoriaBean")
@RequestScoped
public class CategoriaBean {
    private TreeNode categoriasTree;
    private Categoria editada = new Categoria();
    private List<SelectItem> categoriasSelect;
    private boolean mostraEdicao = false;

    public void novo() {
        Categoria pai = null;
        if (this.editada.getCodigo() != null) {
            CategoriaRN categoriaRN = new CategoriaRN();
            pai = categoriaRN.carregar(this.editada.getCodigo());
        }
        this.editada = new Categoria();
        this.editada.setPai(pai);
        this.mostraEdicao = true;
    }

    public void selecionar(NodeSelectEvent event) {
        this.editada = (Categoria) event.getTreeNode().getData();
        Categoria pai = this.editada.getPai();
        if (this.editada != null && pai != null && pai.getCodigo() != null) {
            this.mostraEdicao = true;
        }
        else {
            this.mostraEdicao = false;
        }
    }

    public void salvar() {
        ContextoBean contextoBean = ContextoUtil.getContextoBean();
        CategoriaRN categoriaRN = new CategoriaRN();
        this.editada.setUsuario(contextoBean.getUsuarioLogado());
        categoriaRN.salvar(this.editada);

        this.editada = null;
        this.mostraEdicao = false;
        this.categoriasTree = null;
        this.categoriasSelect = null;
    }

    public void excluir() {
        CategoriaRN categoriaRN = new CategoriaRN();
        categoriaRN.excluir(this.editada);

        this.editada = null;
        this.mostraEdicao = false;
        this.categoriasTree = null;
        this.categoriasSelect = null;
    }

    public TreeNode getCategoriasTree() {
        if (this.categoriasTree == null) {
            ContextoBean contextoBean = ContextoUtil.getContextoBean();
            CategoriaRN categoriaRN = new CategoriaRN();
            List<Categoria> categorias = categoriaRN.listar(contextoBean.getUsuarioLogado());
            this.categoriasTree = new DefaultTreeNode(null, null);
            this.montarDadosTree(this.categoriasTree, categorias);
        }

        return this.categoriasTree;
    }

    private void montarDadosTree(TreeNode pai, List<Categoria> lista) {
        if (lista != null && lista.size() > 0) {
            TreeNode filho = null;
            for (Categoria categoria : lista) {
                filho = new DefaultTreeNode(categoria, pai);
                this.montarDadosTree(filho, categoria.getFilhos());
            }
        }
    }

    public List<SelectItem> getCategoriasSelect() {
        if (this.categoriasSelect == null) {
            this.categoriasSelect = new ArrayList<SelectItem>();
            ContextoBean contextoBean = ContextoUtil.getContextoBean();
            CategoriaRN categoriaRN = new CategoriaRN();
            List<Categoria> categorias = categoriaRN.listar(contextoBean.getUsuarioLogado());
            this.montarDadosSelect(this.categoriasSelect, categorias, "");
        }

        return categoriasSelect;
    }

    private void montarDadosSelect(List<SelectItem> select, List<Categoria> categorias, String prefixo) {
        SelectItem item = null;
        if (categorias != null) {
            for (Categoria categoria : categorias) {
                item = new SelectItem(categoria, prefixo + categoria.getDescricao());
                item.setEscape(false);
                select.add(item);
                this.montarDadosSelect(select, categoria.getFilhos(), prefixo + "&nbsp;&nbsp;");
            }
        }
    }

    public Categoria getEditada() {
        return editada;
    }

    public void setEditada(Categoria editada) {
        this.editada = editada;
    }

    public boolean isMostraEdicao() {
        return mostraEdicao;
    }

    public void setMostraEdicao(boolean mostraEdicao) {
        this.mostraEdicao = mostraEdicao;
    }

    public void setCategoriasTree(TreeNode categoriasTree) {
        this.categoriasTree = categoriasTree;
    }

    public void setCategoriasSelect(List<SelectItem> categoriasSelect) {
        this.categoriasSelect = categoriasSelect;
    }
}

Класс RN (из объекта бизнес-правила):

public class CategoriaRN {
    private CategoriaDAO categoriaDAO;

    public CategoriaRN() {
        this.categoriaDAO = DAOFactory.criarCategoriaDAO();
    }

    public List<Categoria> listar(Usuario usuario) {
        return this.categoriaDAO.listar(usuario);
    }

    public Categoria salvar(Categoria categoria) {
        Categoria pai = categoria.getPai();

        if (pai == null) {
            String msg = "A Categoria " + categoria.getDescricao() + " deve ter um pai definido";
            throw new IllegalArgumentException(msg);
        }

        boolean mudouFator = pai.getFator() != categoria.getFator();

        categoria.setFator(pai.getFator());
        categoria = this.categoriaDAO.salvar(categoria);

        if (mudouFator) {
            categoria = this.carregar(categoria.getCodigo());
            this.replicarFator(categoria, categoria.getFator());
        }

        return categoria;
    }

    private void replicarFator(Categoria categoria, int fator) {
        if (categoria.getFilhos() != null) {
            for (Categoria filho : categoria.getFilhos()) {
                filho.setFator(fator);
                this.categoriaDAO.salvar(filho);
                this.replicarFator(filho, fator);
            }
        }
    }

    public void excluir(Categoria categoria) {
        this.categoriaDAO.excluir(categoria);
    }

    public void excluir(Usuario usuario) {
        List<Categoria> lista = this.listar(usuario);
        for (Categoria categoria : lista) {
            this.categoriaDAO.excluir(categoria);
        }
    }

    public Categoria carregar(Integer categoria) {
        return this.categoriaDAO.carregar(categoria);
    }

    public void salvarEstruturaPadrao(Usuario usuario) {
        Categoria despesas = new Categoria(null, usuario, "DESPESAS", -1);
        despesas = this.categoriaDAO.salvar(despesas);

        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Moradia", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Alimentação", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Vestuário", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Deslocamento", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Cuidados Pessoais", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Educação", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Saúde", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Lazer", -1));
        this.categoriaDAO.salvar(new Categoria(despesas, usuario, "Despesas Financeiras", -1));

        Categoria receitas = new Categoria(null, usuario, "RECEITAS", 1);
        receitas = this.categoriaDAO.salvar(receitas);

        this.categoriaDAO.salvar(new Categoria(receitas, usuario, "Salário", 1));
        this.categoriaDAO.salvar(new Categoria(receitas, usuario, "Restituições", 1));
        this.categoriaDAO.salvar(new Categoria(receitas, usuario, "Rendimento", 1));
    }
}

Сопоставленный класс:

@Entity
public class Categoria implements Serializable {

    private static final long serialVersionUID = -4996563889965803475L;


    @Id
    @GeneratedValue
    private Integer codigo;

    @ManyToOne
    @JoinColumn(name = "categoriaPai", nullable = true)
    @ForeignKey(name = "fkCategoriaCategoria")
    private Categoria pai;

    @ManyToOne
    @JoinColumn(name = "usuario")
    @OnDelete(action=OnDeleteAction.CASCADE)
    @ForeignKey(name = "fkCategoriaUsuario")
    private Usuario usuario;

    private String descricao;

    private int fator;

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.REMOVE)
    @JoinColumn(name = "categoriaPai", updatable = false)
    @OrderBy(value="descricao asc")
    private List<Categoria> filhos;

    public Categoria() { }

    public Categoria(Categoria pai, Usuario usuario, String descricao, int fator) {
        this.pai = pai;
        this.usuario = usuario;
        this.descricao = descricao;
        this.fator = fator;
    }

    public Integer getCodigo() {
        return codigo;
    }

    public void setCodigo(Integer codigo) {
        this.codigo = codigo;
    }

    public Categoria getPai() {
        return pai;
    }

    public void setPai(Categoria pai) {
        this.pai = pai;
    }

    public Usuario getUsuario() {
        return usuario;
    }

    public void setUsuario(Usuario usuario) {
        this.usuario = usuario;
    }

    public String getDescricao() {
        return descricao;
    }

    public void setDescricao(String descricao) {
        this.descricao = descricao;
    }

    public int getFator() {
        return fator;
    }

    public void setFator(int fator) {
        this.fator = fator;
    }

    public List<Categoria> getFilhos() {
        return filhos;
    }

    public void setFilhos(List<Categoria> filhos) {
        this.filhos = filhos;
    }

    public static long getSerialversionuid() {
        return serialVersionUID;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((codigo == null) ? 0 : codigo.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Categoria other = (Categoria) obj;
        if (codigo == null) {
            if (other.codigo != null)
                return false;
        } else if (!codigo.equals(other.codigo))
            return false;
        return true;
    }

}

И у меня есть конвертер:

@FacesConverter(forClass = Categoria.class)
public class CategoriaConverter implements Converter {

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        if (value != null && value.trim().length() > 0) {
            Integer codigo = Integer.valueOf(value);
            try {
                CategoriaRN categoriaRN = new CategoriaRN();
                return categoriaRN.carregar(codigo);
            }
            catch (Exception e) {
                throw new ConverterException("Não foi possível encontrar a categoria de código " + value + ". " + e.getMessage());
            }
        }
        return null;
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        if (value != null) {
            Categoria categoria = (Categoria) value;
            return categoria.getCodigo().toString();
        }
        return "";
    }

}

Эта система из книги, которую я изучаю

Если вам нужен еще один класс, просто скажите мне, что я действительно хочу понять, что происходит

Я ценю, если кто-нибудь может мне помочь.