JSF Drop Down Converter Problems

Question

I am having problems with JSF 1.1_01 (MyFaces 1.1.1).
I have created page called page.jsp as follows:
<h:selectOneMenu value="#{test.selectedDevice}" id="deviceTypeList" styleClass="dropdown">
<f:selectItems value="#{test.deviceTypes}" />
<ajax:support action="#{test.loadDevice}" event="onchange" reRender="t2,t3,t4,t5"/>
</h:selectOneMenu>
It is uses managed bean called TestBean.java:
public class TestBean {
public List getDeviceTypes(){
     logger.info(" *** In getDeviceTypes Backing Bean*** ");
     List<SelectItem> models = new ArrayList<SelectItem>();
     List<SelectItem> deviceTypes = new ArrayList<SelectItem>();
// Gets Data from Hibernate Query . It returns List of Device Types
     models = deviceManager.getDeviceTypes();
     logger.info(" *** DeviceType List Size=*** "+models.size());
     for (Iterator it = models.iterator(); it.hasNext();) {
          System.out.println("Inside For Loop Iterator size="+models.size());
          Object[] row = (Object[]) it.next();
     System.out.println("ID: " + row[0]); // prints data
     System.out.println("Name: " + row[1]); //prints data
// Below line results in error : does not have a Converter
     deviceTypes.add(new SelectItem(row[0],row[1]+""));
          return deviceTypes;
During page rendering, page.jsp throws following exception:
javax.servlet.ServletException: Value is no String and component _id0:deviceTypeList does not have a Converter
Is this bug with MyFaces 1.1.1 or I have made something wrong?
I am a newbie & didnt know much about Converters hence read some examples from the web saying to have getObject() & getString methods . So i added below Class but not sure how to align with page.jsp page.
public class DeviceTypeConverter implements Converter{
     protected final Log logger = LogFactory.getLog(getClass());
     public Object getAsObject(FacesContext facesContext, UIComponent uiComponent, String s) throws ConverterException {
               DeviceDao dao = new DeviceDao();
               return dao.getdeviceTypes().(Long.decode(s));
               public String getAsString(FacesContext facesContext, UIComponent
               uiComponent, Object o) throws ConverterException {
               if(o!= null)
               logger.debug(o.toString());
               try {
               if((o!= null) && (o instanceof DeviceType)){
               DeviceType dt = (DeviceType) o;
               return ""+dt.getId();
               else
               return "0";
               } catch (Exception e) {
               logger.error(e);
               throw new ConverterException();
Any pointers/suggestions on how to write a Converter & help in resolving the error will be highly appreciated
Regards
Bansi

Answer 1

Glad you found a way to make it work. I've got some ideas on improving this, as it is a little hacked together right now.
But first things first...
Does the models ArrayList really contain SelectItem
objects??? If so, why would you bother transfering
each SelectItem if it's already built.The models ArrayList doesnt contain SelectItems objects. It stores List of
DeviceType objects retrieved from Database via Spring business layer i.e.
models = deviceManager.getDeviceTypes() Then this line of code is wrong.
    List<SelectItem> models = new ArrayList<SelectItem>();You are not creating a list of SelectItem objects. You are creating a list of DeviceType objects. It should be:
    List<DeviceType> models = new ArrayList<DeviceType>();
What are the objects represented by row[0] and
row[1]?As models ArrayList contains Array of Objects i.e. multiple records (or
rows) i am using Object[] row to store the values. That means row[0] &
row[1] will contain column values for e.g. row[0] contains id values viz. 1,2,3
etc
What object does setSelectedDevice expect to
receive?setSelectedDevice sets the selected Device id value submitted from JSF
page into Backing BeanThis isn't what I was asking. I just want to know the java type object represented by row[0], row[1], and the java type object passed into setSelectedDevice. e.g: String, Integer, DeviceType, etc, or perhaps even the java primitive (int, char, boolean, etc...) if that's the case.
These two questions are related and important. The java object represented by row[0] needs to be the java object passed into the setSelectedDevice. Actually, just by looking at your code, I can tell you the setSelectedDevice requires a String argument. My bet is that row[0] is not a String.
As a side note... You shouldn't be making DB calls
from your bean getters or setters. DB calls can mean
a performance hit, and JSF will call the getters and
setters multiple times per page request (which means
you'll be doing multiple DB calls).... i started working on JSF-Spring-Hibernate project i always asked the
question on Best Practices and i totally agree with your point. Hence i use
Spring in the middle layer therefore i always call my Managers from
Backing Bean for e.g. TestBean calls deviceManager for
save,update,delete, getDeviceTypes,getDeviceTypes(String id)
Also i have a question for you on the best practice. What should be the
arguments to these save, update methods.
Do you think it should be individual field values as specified in backing
bean or should it be an objectUmm, I don't know. I'm sorry, I won't be much help to you here. I have not worked with Spring or Hibernate (yet). I can't advise you on those technologies (or how JSF would interface best with them).
Check out this topic and you might be able to glean some useful information from it.
http://forum.java.sun.com/thread.jspa?threadID=784351
Hope I've been of some help!
CowKing