Details for the Backing Bean Management of JSF

Backing Beans

Sometimes, it is convenient to design a bean that contains some or all component objects of a web form. Such a bean is called a backing bean for the web form.For example, we can turn the BackingBean into a backing bean by adding properties or updating properties for the component you need on the form like this as follow:

edit.jsp:

<%@ page language="java" pageEncoding="UTF-8"%> <%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %> <%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %> <f:view> <h:form id="form1"> <h:panelGrid binding="#{backingBean.component}"/> <h:commandButton value="submit" actionListener="#{backingBean.action}"></h:commandButton> </h:form> </f:view>

 

BackingBean.java:

package com.ibm.bean; import java.util.Iterator; import javax.faces.application.Application; import javax.faces.component.UIComponent; import javax.faces.component.UIInput; import javax.faces.component.UIPanel; import javax.faces.component.UIViewRoot; import javax.faces.component.html.HtmlInputText; import javax.faces.component.html.HtmlOutputText; import javax.faces.context.FacesContext; import javax.faces.event.ActionEvent; import javax.servlet.http.HttpServletRequest; public class BackingBean { private FacesContext context = FacesContext.getCurrentInstance(); private UIViewRoot root = context.getViewRoot(); private Application application = context.getApplication(); private UIComponent component; private UIInput input; public UIInput getInput() { if(input == null){ input = new UIInput(); } return input; } public void setInput(UIInput input) { this.input = input; } public BackingBean() { } public UIComponent getComponent() { if (component == null) { component = new UIPanel(); } System.out.println(component); return component; } // initialization by block or by static block { try { HtmlOutputText out = (HtmlOutputText) context.getApplication() .createComponent(HtmlOutputText.COMPONENT_TYPE); HttpServletRequest request = (HttpServletRequest)context.getExternalContext().getRequest(); System.out.println("request.getRealPath()="+request.getRealPath(null)); System.out.println("request.getRequestURI()="+request.getRequestURI()); System.out.println("request.getContextPath()="+request.getContextPath()); System.out.println("request.getServletPath()="+request.getServletPath()); System.out.println("getViewId()="+context.getViewRoot().getViewId()); System.out .println("----------this is the out component--------------" + this.getComponent()); out.setId("id1"); out.setValue("buttonName:"); HtmlInputText in = (HtmlInputText) context.getApplication() .createComponent(HtmlInputText.COMPONENT_TYPE); in.setRendered(false); in.setId("button"); in.setValueBinding("buttonName", application .createValueBinding("#{tableData.buttonName}")); this.getComponent().getChildren().add(out); this.getComponent().getChildren().add(in); } catch (Throwable t) { System.out.println("java.lang.Throwable exception encountered..." + t.getMessage()); t.printStackTrace(); } } public void setComponent(UIComponent component) { this.component = component; } public void action(ActionEvent event){ HtmlInputText in = (HtmlInputText)findComponentInRoot("button"); in.setValue("@@@@"); in.setRendered(true); System.out.println("getClientId="+event.getComponent().getClientId(context)); } /** * <p> * Return the {@link UIComponent} (if any) with the specified <code>id</code>, * searching recursively starting at the specified <code>base</code>, and * examining the base component itself, followed by examining all the base * component's facets and children. Unlike findComponent method of * {@link UIComponentBase}, which skips recursive scan each time it finds a * {@link NamingContainer}, this method examines all components, regardless * of their namespace (assuming IDs are unique). * * @param base Base {@link UIComponent} from which to search * @param id Component identifier to be matched */ public static UIComponent findComponent(UIComponent base, String id) { // Is the "base" component itself the match we are looking for? if (id.equals(base.getId())) { return base; } // Search through our facets and children UIComponent kid = null; UIComponent result = null; Iterator kids = base.getFacetsAndChildren(); while (kids.hasNext() && (result == null)) { kid = (UIComponent) kids.next(); if (id.equals(kid.getId())) { result = kid; break; } result = findComponent(kid, id); if (result != null) { break; } } return result; } /** * find component based on root component of page, it calls <code>findComponent</code> * method to find component * * @param id * id of component which should be found * @return * component which has the id */ public static UIComponent findComponentInRoot(String id) { UIComponent ret = null; FacesContext context = FacesContext.getCurrentInstance(); if (context != null) { UIComponent root = context.getViewRoot(); ret = findComponent(root, id); } return ret; } }

 

 

When the component tree for the form is built, the getComponent method of the backing bean is called, but it returns null. As a result, an output component is constructed and installed into the backing bean with a call to setComponent.

Backing beans have their uses, but they can also be abused. You should not use the user interface components as a repository for business data. If you use backing beans for your forms, you should still use beans for business objects.

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