Month: January 2008

This is one problem i faced when i worked with select-many and select-one menus in Java Server Faces. For any one who have worked with JSF knows that you have to use custom converters in order to populate select-many and select-on menus with ur own data types.

if i elaborate on this a little bit, Select menus are not just there to show simple value-label pairs. you can give directly an object to its value and one of its fields as the label. for an example,

public ArrayList<SelectItem> getLandSelectList() {
if (landSelectList != null) {
return landSelectList;
}
    landSelectList = new ArrayList<SelectItem>();
List<Land> landList = this.getLandList();
for (int i = 0; i < landList.size(); i++) {
        landSelectList.add(new SelectItem(landList.get(i), landList.get(i)
.getLandsName_DE()));
}
return landSelectList;
}

The returning Select list can be taken to a select one or a select many list box like..

<h:selectOneMenu id=”listBoxLand”
value=”#{userManagerBean.land}” required=”true”>
<f:selectItems value=”#{userManagerBean.landSelectList}” />
</h:selectOneMenu>
<h:message for=”listBoxLand” />

This component will set the selected land object directly to the backing bean. If you used simple value(some text or the id) – label pair. you should again query for the object from the selected id and save in the backing bean. but in this way that extra trouble will be handled by JSF.

The problem is if you do it just like this with out anything else.. you will get a wired validation error saying “Validation Error: Value is not valid“. This is where you start googling and debugging. Well after some hours of googling..(couldn’t do much debugging because this is a exception thrown by JSF framework) and reading about 10 to 20 forums i found out that the object which is loaded and the object wich was selected will be compared when setting to the backing bean. So if your object’s Class has not overridden the equals method this error message is shown.

So what you have to do is. if you are using your own data Objects for the select menus or in that case for any other JSF tag where you will use converters. You have to override the Equals method. Probably do the comparison with the Id, or with some unique value in that data Object. That’s it.. The problem solved. In my case the equals methods looks like

// overridden equals method
public boolean equals(Object obj) {
if (!(obj instanceof Land)) {
return false;
}
Land land = (Land) obj;

return (this.id == land.id);

}

Yeah hope this will be useful to some one.. !! I will write another post on how to use Java Collections when working with Select-Many menus.

So yeah !! I thought of writing something about JSF. Since am working with it for Nealy 3 months now. So how about custom message handling for starters !! 🙂

JSF message tag is pretty useful in many places. for an example, for the use of validators. but what i wanted to write here is, not how a message is shown after validation.

Think after some database transaction you wanted to say “Transaction is successful or not successful” or in some random scenario if you wanted to show a message in anywhere in your web-page at anytime, you can do that from your backing bean with out much effort.

I will take the tomahawk fileupload tag as an example JSF tag. so in the JSP side it will look like

	
               value="#{bbaBean.theFile}" storage="file"
               styleClass="fileUploadInput"
               required="true">
        

               errorstyle="Color: red;">



                 action="#{bbaBean.uploadFile}" styleclass="linkbox">

And when the upload button is clicked the uploadFile method will be invoked in our backing bean. which will look like..

public String uploadFile throws IOException {

       FacesMessage messageErr =
               new FacesMessage(FacesMessage.SEVERITY_ERROR,
                     "ERROR : ",
                     "XML File you have uploaded is not compatible");

       FacesMessage messageSuc = new FacesMessage(
              "The XML File You have uploaded is successfully
                                           added to the Database");

       FacesContext fc = FacesContext.getCurrentInstance();

       try {
              //TODO: Transaction or logic....
               fc..addMessage("form1:fileupload", messageSuc);
       } catch(Exception e) {
               fc.addMessage("form1:fileupload", messageErr);
       }
}

Simply that is it. So when an exception occurs your JSP page shows the custom error message. One other thing is you can set the message type too. if its and error message as i have shown make it’s SEVERITY to ERROR. and add an error style class for the tag. so your error message will be shown different than the other messages..

so yeah enjoy..