@Inject PersonDao在@FacesConverter类中是空的

Question

我试图从selectOneMenu获得一个具有姓名，姓氏等字段的对象。这是我的表单:

<h:form>
<p:outputLabel value="Persons: " />
<p:selectOneMenu value="#{personBean.person}">
    <f:selectItem itemLabel="Select Person" itemValue="" noSelectionOption="true"/>
    <f:selectItems itemLabel="#{person.firstName}" itemValue="#{person}" var="person" value="#{personBean.persons}" />
</p:selectOneMenu>
<br /><br />
<p:commandButton value="Submit"
    action="#{personBean.showSomething()}" icon="ui-icon-check" />

我不明白……我哪里做错了?我怎样才能得到那个对象?
我已经尝试了几天，但我还没有设法解决这个问题…我尝试使用Converter，但我一直得到npe。

编辑
这是我的转换器:(我试图在我的DAO的帮助下从我的postgres db中获得对象)

@Named
@FacesConverter(forClass=Person.class)
public class PersonConverter implements Converter {
    @Inject
    private PersonDao personDao;
    @Override
    public Object getAsObject(FacesContext arg0, UIComponent component, String submittedValue) {
        if (submittedValue == null || submittedValue.isEmpty()) {
            return null;
        }
        try {
            Person p = personDao.findById(Long.valueOf(submittedValue));
            return p;
        } catch (NumberFormatException e) {
            throw new ConverterException(new FacesMessage(submittedValue + " is not a valid Person ID"), e);
        }
    }
    @Override
    public String getAsString(FacesContext arg0, UIComponent arg1, Object arg2) {
        if (arg2 == null) {
            return "";
        }
        if (arg2 instanceof Person) {
            return String.valueOf(((Person) arg2).getId());
        } else {
            throw new ConverterException(new FacesMessage(arg2 + " is not a valid Person"));
        }
    }
}

这就是我得到NPE Person p = personDao.findById(Long.valueOf(submittedValue));的地方
find()方法在其他任何地方都可以使用…当我使用调试器时，我注意到personDao是空的。我怎样才能解决这个问题?

Answer 1

• 在页面中:

          <p:selectOneMenu value="#{personBean.person}">
              <f:selectItem itemLabel="Select Person" itemValue="" noSelectionOption="true"/>
              <f:selectItems itemLabel="#{person.firstName}" itemValue="#{person}" var="person" value="#{personBean.persons}" />
              <f:converter binding="#{personConverter}" />
              <f:attribute name="attrpersons" value="#{personBean.persons}" />                    
          </p:selectOneMenu>
  

• 在Person bean中:

  你必须实现toString和equals方法

• 最后你必须添加转换器类:

  @Named
  public class PersonConverter implements Converter{
      public PersonConverter(){}
      @Override
        public Object getAsObject(FacesContext facesContext, UIComponent component, String submittedValue) {
            List<Person> persons = (List<Person>)component.getAttributes().get("attrpersons");
          if (submittedValue.trim().equals("")) {
              return null;
          } else {
              Iterator<Person> it = persons.iterator();
              while(it.hasNext()){
                  Person p = it.next();
                  if(p.toString().equals(submittedValue))
                      return p;                
              }
          }
          return null;
      }
      @Override
      public String getAsString(FacesContext facesContext, UIComponent component, Object value) {
          if (value == null) {
              return "";
          } else {
              return value.toString();
          }
      }
  }