To map backing bean from a selected drop-down value

[N Deepu]

Hi all,

I've a requirement to map the backing bean class from the object that is selected from the drop-down in my jsf page. How can i do this?
Eg. I've chosen Person from the drop down - I should retrieve a class called Person.java.

Kindly help me with the same..

Thanks in advance

[Vijay Tidake]

Hi,

This is what I tried with the Animal and Person bean.

 <h:form id="form">
             	<h:selectOneMenu valueChangeListener="#{bean.valueChanged}">
                	<f:selectItems value="#{bean.list}" var="item"></f:selectItems>                
                </h:selectOneMenu>                
   </h:form>

import java.util.LinkedList;
import java.util.List;

import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.event.ValueChangeEvent;
import javax.faces.model.SelectItem;

@ManagedBean(name = "bean")
public class Bean {

	List<SelectItem> list = null;

	@PostConstruct
	public void init() {

		list = new LinkedList<SelectItem>();

		for (EnumInstance e : EnumInstance.values()) {
			list.add(new SelectItem(e.getClassInstance(), e.name()));
		}
	}

	public List<SelectItem> getList() {
		return list;
	}

	public void setList(List<SelectItem> list) {
		this.list = list;
	}

	public void valueChanged(ValueChangeEvent v) {
		System.out.println("Hi " + v.getNewValue());
	}
}

public enum EnumInstance {
	Person(Person.class), Animal(Animal.class);

	Class classInstance = null;

	EnumInstance(Class classInstance) {
		this.classInstance = classInstance;
	}

	public Class getClassInstance() {
		return classInstance;
	}

}

Hope this helps
Thanks

[N Deepu]

Hi,

You mean to say u're calling person and animal class from the enum class?

[Vijay Tidake]

Yes,

As per your question ,you want the instance of a class,that is selected in dropdown right?

Thanks

[N Deepu]

Hi,

I want to call the class from the object that is selected. In your example, If I select Person, I should call the Person class and perform the corresponding functionality there.

Thanks

[N Deepu]

Hi again,

I was trying to execute what you've replied here. But it is not mapping the value change listener class on change of the option even though I've given
"Onchange = submit()"

[Tim Holloway]

You have a problem with definitions here, "Ns". You're not looking to "retrieve" or "call" a class. What you want to do is retrieve an instance of a class.

Beyond that there are several other difficulties.

First of all, you cannot specify a complex (class) object as the key part of a SelectItem. The SelectItem is rendered as HTML, and HTML is text-only, so if you provide a binary object as the key, it will be converted to a String, and by default, that string will be a meaningless sequence of characters of little or no practical use. A better approach is to put all your objects in a Map where each entry has a text key, use that key to instantiate the SelectItem, then have the action handler use that key to retrieve the actual object from the Map.

Secondly, you can't just "submit()". You need proper AJAX support if you want to be able to be notified when a selectOneMenu's selected value has changed.

[N Deepu]

Hi,

Thanks. I'll try what you said..

[N Deepu]

Hi again Tim,

I follwed what you said. I've a Hashmap which has "Key-Label to be displayed" and "Value-The backing bean name". I'm able to retrieve the corresponding name after I select from the drop down. The value received is in the string format. How do I now create an instance of this and call the corresponding class?

Eg. I selected Address, getPropertiesMap().get(event.getNewValue() is giving me the fully qualified name - com.backingbean.Address which is now in string format.

Thanks in Advance

[Tom mmeke]

ns deep wrote:Hi again Tim,

I follwed what you said. I've a Hashmap which has "Key-Label to be displayed" and "Value-The backing bean name". I'm able to retrieve the corresponding name after I select from the drop down. The value received is in the string format. How do I now create an instance of this and call the corresponding class?

Eg. I selected Address, getPropertiesMap().get(event.getNewValue() is giving me the fully qualified name - com.backingbean.Address which is now in string format.

Thanks in Advance

// Backingbean
private Map<Integer,Person> map;
private int selectedValue;
// Getters & Setters


// JSF
<h:selectOneMenu value="#{backingbean.selectedValue}" >
     <f:selectItems value="#{backingbean.map}" var="entry" itemValue="#{entry.key}" itemLabel="#{entry.value.firstname}" />
</h:selectOneMenu>

Should look something like this. (Haven't tested it)

[N Deepu]

Hi,

I'm not getting the answer required. This is bugging me since 3 days. Kindly help me.

//constructor
public UserBean() {

		ResourceLoader.loadBundle("properties file name");
		Set<Object> keys=ResourceLoader.getPropertiesMap().keySet();

		list = new LinkedList<SelectItem>();
		list.add(new SelectItem("Select"));

		Iterator<Object> It = keys.iterator();
		while (It.hasNext()) {
			Object HostNow = (Object)(It.next());

			System.out.println(HostNow + " - " + ResourceLoader.getPropertiesMap().get(HostNow));
			list.add(new SelectItem(ResourceLoader.getPropertiesMap().get(HostNow)));
		}
	}

//ValueChange Listener class
String instance = new String();
public void valueChanged(ValueChangeEvent event) throws InstantiationException, IllegalAccessException
	{
		instance = (String)event.getNewValue();

		try {
			Class cls = Class.forName("instance");
			cls.getConstructors();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}

	}

This is the exception I'm getting

java.lang.ClassNotFoundException: instance
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1676)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1521)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at com.infosys.reuse.Bean.UserBean.valueChanged(UserBean.java:61)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.el.parser.AstValue.invoke(AstValue.java:262)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:278)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:102)
at javax.faces.event.MethodExpressionValueChangeListener.processValueChange(MethodExpressionValueChangeListener.java:140)
at javax.faces.event.ValueChangeEvent.processListener(ValueChangeEvent.java:130)
at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:773)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:746)
at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1161)
at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:72)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:308)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:498)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:394)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

[Tim Holloway]

The server is looking for the following file in your WAR:

/WEB-INF/classes/instance.class

using the Class.forName("instance") as its directive.

I don't think you really wanted to do that, since class names shouldn't begin with lower-case letters and use of the default package is discouraged.

[Tom mmeke]

1. Every reference to ResourceLoader is static ?
2. Why are you first getting the KeySet, then iterate over the KeySet, to finally request the value from the properties map for each key ?
Why not just iterate the PropertiesMap from the beginning ?
3. Class.forname() expects a classname as parameter (duh), something like 'com.yourpackage.ResourceLoader', and not just the variable you gave an instance of a class ...

Besides, like Tim told you before, you can't expect JSF to give you an entire object as selected value.
Use my previous example, and change valueChanged to this.

public void valueChanged(ValueChangeEvent event) throws InstantiationException, IllegalAccessException  
    {  
        selectedValue = event.getNewValue();  
  
        try {  
            Class cls = Class.forName(ResourceLoader.getPropertiesMap().get(selectedValue).getClass().className());  
            cls.getConstructors();  
        } catch (ClassNotFoundException e) {  
            e.printStackTrace();  
        }  
  
    }

Still not sure what your actually trying to achieve with this snippet.
Nevertheless, there is something seriously wrong with your code.

[N Deepu]

Thanks for the reply both of you.

This is what I changed and I'm now able to call the method of the Object being selected.

@SuppressWarnings({ "rawtypes", "unchecked" })
	public void valueChanged(ValueChangeEvent event) throws InstantiationException, IllegalAccessException, SecurityException, NoSuchMethodException
	{

		instance = (String)event.getNewValue();
		System.out.println(instance);
		try {
			Class cls = Class.forName(instance);
			System.out.println("Name "+cls.getClass().getName());
			Method meth = cls.getMethod("test",null);
			System.out.println("Public method found: " +meth.toString());

			Object obj = cls.newInstance();
			meth.invoke(obj, null);

		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}catch (NoSuchMethodException ex){
             System.out.println("Method either doesn't exist or is not public: " + ex.toString());
        }
	}