JSF SelectOneMenu使用标签作为值的noSelectionOption？

Question

在"创建新用户"jsf页面中,我有一个带有自定义转换器的SelectOneMenu和一个noSelectionOption selectItem,如下所示:(无关代码无关)

NewUser.xhtml

<h:form>
<h:selectOneMenu value="#{newUserController.user.department}" 
                 required="true" converter="departmentConverter">
    <f:selectItem itemLabel="Select a department" noSelectionOption="true"/>
    <f:selectItems value="#{newUserController.departments}"
                   var="dep" itemLabel="#{dep.name}" itemValue="#{dep}"/>
</h:selectOneMenu>
<p:commandButton action="#{newUserController.saveUser}"
                 value="#{bundle.Save}"
                 ajax="false"/>
</h:form>

NewUserController.java

@ManagedBean
@ViewScoped
public class NewUserController implements Serializable {
private static final long serialVersionUID = 10L;

@EJB private UserBean userBean;
private List<Department> departments;
private User user;

public NewUserController () {
}

@PostConstruct
public void init(){
    user = new User();
    departments = userBean.findAllDepartments();
}

public User getUser() {
    return user;
}

public void setUser(User user) {
    this.user = user;
}

public List<Department> getDepartments(){
    return departments;
}

public String saveUser() {
    // Business logic
}
}

DepartmentConverter.java

@FacesConverter(value="departmentConverter")
public class DepartmentConverter extends EntityConverter {
    public DepartmentConverter(){
        super(Department.class);
    }
}

所有实体的超级转换器

public class EntityConverter<E> implements Converter{
protected Class<E> entityClass;

public EntityConverter(Class<E> type) {
    entityClass = type;
}

@Override
public Object getAsObject(FacesContext facesContext, UIComponent component, String value) {
    if (value == null || value.length() == 0) {
        return null;
    }
    try {
        InitialContext ic = new InitialContext();
        UserBean ub = (UserBean)ic.lookup("java:global/CompetenceRegister/UserBean");
        return ub.find(entityClass, getKey(value));
    } catch (NamingException e) {
        return null;
    }
}

Long getKey(String value) {
    Long key;
    key = Long.valueOf(value);
    return key;
}

String getStringKey(Long value) {
    StringBuilder sb = new StringBuilder();
    sb.append(value);
    return sb.toString();
}

@Override
public String getAsString(FacesContext facesContext, UIComponent component, Object object) {
    if (object == null) {
        return null;
    }
    if (object instanceof AbstractEntity) {
        AbstractEntity e = (AbstractEntity) object;
        return getStringKey(e.getId());
    }
    else
        throw new IllegalArgumentException("object " + object + " is of type " + object.getClass().getName() + "; expected type: " + entityClass.getName());
}

}

但是,当我发布选择了"选择部门"选项的表单时,它会将标签发送到转换器中的getAsObject而不是null,从而导致转换器在getKey中抛出异常(尝试将包含id的String转换为很长).将selectItem的itemValue属性设置为null无效.该系列中的物品与转换器完美配合.有没有人知道造成这种情况的原因是什么？

更新我忘了提到一件有趣的事情; 如果我从SelectOneMenu中删除转换器属性,则noSelectionAttribute可以正常工作,但由于默认转换器不知道如何转换我的对象,因此帖子无法选择真正的部门.这可能意味着noSelectionOption = true时应该发送它的标签,而不是和转换器以某种方式预计处理呢？

Answer 1

我的问题是切换到使用SelectOneMenu的converter属性而不是使用FacesConverter的forClass属性.

交换

@FacesConverter(value="departmentConverter")
public class DepartmentConverter extends EntityConverter {
public DepartmentConverter(){
    super(Department.class);
}
}

至

@FacesConverter(forClass=Department.class)
public class DepartmentConverter extends EntityConverter {
public DepartmentConverter(){
    super(Department.class);
}
}

导致我自己的转换器用于实际值,而当NoSelectionOption属性设置为true时,使用默认转换器(空转换器？我无法找到它的源代码).我的理论是,将此属性设置为true会将值的类型设置为null,并将标签作为值,使其转到特殊转换器,始终返回null或类似的值.使用converter属性而不是forClass会导致我自己的转换器始终被使用而不管类型如何,因此我必须自己处理作为值发送的标签.