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Setting select items programatically

Riaan Nel

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posted 15 years ago

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Hi everybody

Is it possible to set the select items of an HtmlSelectOneMenu through actual Java code, instead of binding it in your JSF page? Thanks a lot for your help!

//Java
import java.util.ArrayList;
import java.util.List;
import javax.faces.component.html.HtmlSelectOneMenu;
import javax.faces.model.SelectItem;

public class TestBean {

private List<SelectItem> items;
    private HtmlSelectOneMenu menu;
    
    /** Creates a new instance of TestBean. */
    public TestBean() {
        items = new ArrayList<SelectItem>();
        items.add(new SelectItem("One"));
        items.add(new SelectItem("Two"));
        items.add(new SelectItem("Three"));

//Can I do something like this?
        //menu.setItems(items);
    }

public List<SelectItem> getItems() {
        return items;
    }

public void setItems(List<SelectItem> items) {
        this.items = items;
    }

public HtmlSelectOneMenu getMenu() {
        return menu;
    }

public void setMenu(HtmlSelectOneMenu menu) {
        this.menu = menu;
    }
}

//JSF
<%@page contentType="text/html" pageEncoding="UTF-8"%>

<%@taglib prefix="f" uri="http://java.sun.com/jsf/core"%>
<%@taglib prefix="h" uri="http://java.sun.com/jsf/html"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">

<f:view>
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
            <title>JSF Test</title>
        </head>
        <body>
            <h:form>
                <h:selectOneMenu id="menu" binding="#{testBean.menu}">
                    <f:selectItems value="#{testBean.items}" />
                </h:selectOneMenu>
            </h:form>
        </body>
    </html>
</f:view>

"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

Riaan Nel

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posted 15 years ago

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"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

Riaan Nel

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posted 15 years ago

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Doesn't anyone know whether this is possible? It doesn't seem like an unreasonable requirement to me. (Please keep in mind that I am new to JSF) Perhaps Ed Burns and Chris Schalk can help?

"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

Riaan Nel

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posted 15 years ago

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Okay, I'm back again, and I think I've made a little bit of progress.

I tried to dynamically add children to the HtmlSelectOneMenu, but I get a NullPointerException after clicking the button on my test page.

Stacktrace:

Initializing Sun's JavaServer Faces implementation (1.2_04-b22-p05) for context '/JSFDemo'
executePhase(RENDER_RESPONSE 6,com.sun.faces.context.FacesContextImpl@52c50d) threw exception
java.lang.NullPointerException
        at org.apache.coyote.tomcat5.CoyoteWriter.write(CoyoteWriter.java:255)
        at com.sun.faces.application.ViewHandlerImpl$WriteBehindStateWriter.write(ViewHandlerImpl.java:834)
        at com.sun.faces.renderkit.html_basic.HtmlResponseWriter.write(HtmlResponseWriter.java:495)
        at com.sun.faces.renderkit.html_basic.MenuRenderer.renderOption(MenuRenderer.java:584)
        at com.sun.faces.renderkit.html_basic.MenuRenderer.renderOptions(MenuRenderer.java:757)
        at com.sun.faces.renderkit.html_basic.MenuRenderer.renderSelect(MenuRenderer.java:811)
        at com.sun.faces.renderkit.html_basic.MenuRenderer.encodeEnd(MenuRenderer.java:335)
        at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:836)
        at javax.faces.component.UIComponent.encodeAll(UIComponent.java:896)
        at javax.faces.render.Renderer.encodeChildren(Renderer.java:137)
        at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:812)
        at javax.faces.component.UIComponent.encodeAll(UIComponent.java:886)
        at javax.faces.component.UIComponent.encodeAll(UIComponent.java:892)
        at com.sun.faces.application.ViewHandlerImpl.doRenderView(ViewHandlerImpl.java:245)
        at com.sun.faces.application.ViewHandlerImpl.renderView(ViewHandlerImpl.java:176)
        at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:106)
        at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
        at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:144)
        at javax.faces.webapp.FacesServlet.service(FacesServlet.java:245)
        //Snip

I've updated my backing bean and JSP page as follows.

//TestBean.java
package test;

import java.util.ArrayList;
import java.util.List;
import javax.faces.component.UIComponent;
import javax.faces.component.UISelectItems;
import javax.faces.component.html.HtmlSelectOneMenu;
import javax.faces.context.FacesContext;
import javax.faces.event.ActionEvent;
import javax.faces.model.SelectItem;

public class TestBean {

private List<SelectItem> englishItems;
    private HtmlSelectOneMenu menu = new HtmlSelectOneMenu();

{
        englishItems = new ArrayList<SelectItem>();
        englishItems.add(new SelectItem("One"));
        englishItems.add(new SelectItem("Two"));
        englishItems.add(new SelectItem("Three"));
    }

/** Creates a new instance of TestBean. */
    public TestBean() {
        
    }

public HtmlSelectOneMenu getMenu() {
        return menu;
    }

public void setMenu(HtmlSelectOneMenu menu) {
        this.menu = menu;
    }

public void ActionListener(ActionEvent evt) {
        List<UIComponent> menuChildren = menu.getChildren();

UISelectItems items = new UISelectItems();
        items.setValueExpression("value", FacesContext.getCurrentInstance().getApplication().getExpressionFactory().createValueExpression(FacesContext.getCurrentInstance().getELContext(), "#{testBean.englishItems}", List.class));
        menuChildren.add(items);
    }

public List<SelectItem> getEnglishItems() {
        return englishItems;
    }

public void setEnglishItems(List<SelectItem> englishItems) {
        this.englishItems = englishItems;
    }
}

//test.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>

<%@taglib prefix="f" uri="http://java.sun.com/jsf/core"%>
<%@taglib prefix="h" uri="http://java.sun.com/jsf/html"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">

<f:view>
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
            <title>JSF Test</title>
        </head>
        <body>
            <h:form>
                <h:selectOneMenu id="menu" binding="#{testBean.menu}" />
                    
                <h:commandButton value="Do Action" actionListener="#{testBean.ActionListener}" />
            </h:form>
        </body>
    </html>
</f:view>

I'd really appreciate it if someone could offer me some advice. Thanks!

Regards,
Riaan

"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw

Ed Burns

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posted 15 years ago

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Hello Riaan Nel,

Thanks for your question. When manipulating the view programmatically you must be aware that you're taking the reins from the tag layer at a fundamental level. Therefore, you must be very aware of how the lifecycle works with respect to the timing of when properties are written to and read from. There's nothing wrong with doing this, but it's just a concern you have to be aware of.

First, make sure TestBean is in request scope. Second, make the getter for the menu property lazily initialize the menu ivar to a new instance of HtmlSelectOneMenu, populated as you've done in your ActionListner (you don't need the actionListener for this purpose any more). Third, make sure to call setValueExpression("value", yourExpression") to the place where you want the selected value to be stored.

Does that work?

Ed

Riaan Nel

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posted 15 years ago

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Hi Ed

Thank you very much for your reply. I changed the scope of my bean from session to request scope, and it works like a charm. Also, thank you for suggesting lazy initialization for my variables, I'll keep that in mind. Once again, many thanks for your help!

Regards,
Riaan Nel

"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw