visual basic 6.0 barcode generator FIGURE 5-3 The backing bean concept illustrated in Java

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FIGURE 5-3 The backing bean concept illustrated
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public String checkUserCredentials() { // call business method to check credentials boolean loginOk = someBusinessMethod(thisgetUserid(), thisgetPassword()); if (loginOk) { // navigate to another page return "success"; } else { FacesContextgetCurrentInstance() addMessage(null, new FacesMessage("Invalid Login!")); // stay on the same page return null; } }
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The backing bean concept shown in a login example
LDAP lookup of the user to determine whether the credentials are valid Figure 5-4 illustrates this example Here is a more advanced example of backing bean usage where a page, employees_ tablejsp, displays a scrollable table of employee information using a corresponding backing bean, EmployeesTablejava In this example, the JSP page uses an HtmlDataTable (<h:dataTable/>) component to display a table of employee records It also uses a custom Scroller UI component that works with methods in the backing bean to handle scrolling events such as next page, previous page, first, and last to navigate through the data being displayed by the table component The JSP page could also have columns for row-level operations such as Edit and Delete When the user clicks Edit, he or she would navigate to a different page to edit the row values in a form Clicking Delete would simply delete the selected record and remain on the same page For this example, the backing bean (EmployeesTablejava) would most probably have the following: Any JavaBean properties that are value bound to components in the page In this example the <h:dataTable> (HtmlDataTable) component could be value bound to a JavaBean property that returns either a List, Result, ResultSet, or an Array For example:
<h:dataTable value="#{EmpTable_BackingempList}" />
This is where the tabular data is initially retrieved; however, to manipulate the data, such as scrolling and so on, the HtmlDataTable component on the page can also be directly bound to a declared instance of UIData (or HtmlDataTable), which has the necessary methods to navigate through the tabular data
Part I:
The JavaServer Faces Framework
At least one instance of a UIData (or HtmlDataTable) component that is directly bound to the DataTable on the page such as:
<h:dataTable value="#{TrainingEventRegistryeventlist}" binding="#{EmpTable_ BackingtableData}" />
In this example EmpTable_BackingtableData is of type UIData and is used to perform data navigation operations on the tabular (List) data that was value bound to HtmlDataTable An action listener method for handling table events such as scrolling through data Figure 5-5 illustrates our example where we have an HtmlDataTable component that is bound to both a UIData instance as well as value bound to a method that returns a List For more detailed UIData and HtmlDataTable examples, 9, which illustrates the Virtual Trainer example application, includes complete coverage of working with tabular data in Faces applications, including how to perform data navigation (scrolling) as well as inserting, updating, and deleting data associated with HtmlDataTable components Before concluding the chapter, here is a final thing to consider when using backing beans It is possible to have more than one backing bean per page, or have multiple pages bound to properties of a single bean, as there is no specified rule on this This is left to the developer s discretion, but having numerous dependencies between multiple pages and multiple backing beans can become very hard to manage However, it s still technically okay to have separate request-scoped managed beans for subsections of your page that get included and reused across multiple pages Again, these are design considerations where the Faces application architect will have to weigh the benefits of standard OOP reuse mechanisms against raising the overall application architecture complexity
employees_tablexhtml @ManagedBean(name="empTable_backing") public class EmployeesTable { private UIData tableData = null; public UIData getTableData() { // initialize tableData, if necessary return tableData; } public List getEmpList() {} public void processScrollEvent( ActionEvent event) {} }
<h:dataTable id="empTable" rows="10" var="row" binding="#{empTable_backingtableData}" value="#{empTable_backingempList}"> Columns </h:dataTable> <t:scroller for="empTable" actionListener="#{emptTable_backingprocessScrollEvent}"/>
FIGURE 5-5
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