java barcode generator example JSF and Ajax in Java

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JSF and Ajax
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To bring the example back to JSF, it s very easy to convert the preceding example to use Ajax, as shown here:
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JSF 20 TIP All of the examples in this chapter show the built-in Ajax support in JSF 20 If you
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are using a version of JSF prior to 20, please see the first edition of this book, or consult the excellent reference Web site: http://jsfmatrixnet/ This site lists all the known JSF+Ajax frameworks in existence, most of which were designed to work with JSF 12
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 10 Transitional//EN" "http://wwww3org/TR/xhtml1/DTD/xhtml1-transitionaldtd"> <html xmlns="http://wwww3org/1999/xhtml" xmlns:h="http://javasuncom/jsf/html" xmlns:f="http://javasuncom/jsf/core"> <h:head> <title>A Simple JavaServer Faces 20 View</title> </h:head> <h:body> <h:form> You entered: #{requestScopeinput} <h:inputText id="input" value="#{requestScopeinput}"> <f:ajax render="@form" /> </h:inputText> </h:form> </h:body> </html>
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PART II
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We simply deleted the button and nested an <f:ajax> element within the input text Now whenever the user moves the cursor out of the input field, the effect will be the same as if that user pressed the button, with the all important exception that the contents of the form will update asynchronously, without a full page refresh That s what the rendered="@form" attribute on the <f:ajax> tag means The <f:ajax> tag will be fully explained later in the chapter, along with its corresponding JavaScript functions To enable this ease of use, there is a whole lot of work being done for you behind the scenes, and you don t need to understand any of it to make great use of Ajax in JSF
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A Simple Ajax Example from JSFReg
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Let s continue with a more practical example from JSFReg: asynchronous validation Let s say we want to add a userid field to the registerxhtml page, and make it so that the availability of the userid is checked automatically as the user fills out the form The beginning lines of the new registerxhtml file are shown here:
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 10 Transitional//EN" "http://wwww3org/TR/xhtml1/DTD/xhtml1-transitionaldtd"> <html xmlns="http://wwww3org/1999/xhtml" xmlns:h="http://javasuncom/jsf/html" xmlns:f="http://javasuncom/jsf/core"> <h:head> <title>A Simple JavaServer Faces Registration Application</title> </h:head>
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Part II:
Extending JavaServer Faces
<h:body> <h:form> <h2>JSF Registration App</h2> <h4>Registration Form</h4> <table> <tr> <td>Userid:</td> <td> <f:ajax render="useridMessage"> <h:inputText label="Userid" id="userid" value="#{userBeanuserid}" required="true"/> <h:message id="useridMessage" for="userid" /> </f:ajax> </td> </tr>
The system is designed so that the <f:ajax> tag has an awareness of the kinds of components it is wrapping so that it can take the appropriate action to best imbue each particular component with Ajax capability Note that there is no explicit validator attached to the field This is because we are using JSR-303 Bean Validation, as shown in the Virtual Trainer from 10 To recall how this works, we simply need to define a Constraint and annotate the setter for the userid property in the UserBean class, as shown here:
private String userid; @UseridUniquenessConstraint public String getUserid() { return userid; } public void setUserid(String userid) { thisuserid = userid; }
The constraint definition is looks like this:
package comjsfcomprefmodel; import import import import import import import javalangannotationDocumented; javalangannotationElementType; javalangannotationRetention; javalangannotationRetentionPolicy; javalangannotationTarget; javaxvalidationConstraint; javaxvalidationConstraintPayload;
@Documented @Constraint(validatedBy = UseridUniquenessConstraintValidatorclass) @Target({ ElementTypeMETHOD, ElementTypeFIELD }) @Retention(RetentionPolicyRUNTIME) public @interface UseridUniquenessConstraint {
12:
JSF and Ajax
String message() default "A user with that userid already exists"; Class< >[] groups() default {}; Class< extends ConstraintPayload>[] payload() default {}; }
And the last piece is the ConstraintValidator class:
package comjsfcomprefmodel; import javaxvalidationConstraintValidator; import javaxvalidationConstraintValidatorContext; public class UseridUniquenessConstraintValidator implements ConstraintValidator<UseridUniquenessConstraint, String> { public boolean isValid(String value, ConstraintValidatorContext ctx) { boolean result = (null != value && 3 < valuelength()); return result; } public void initialize(UseridUniquenessConstraint arg0) { } }
PART II
Now, the presence of the <f:ajax> tag wrapping the input field and its corresponding message will cause the form to be submitted, processed, and rendered, partially In this case, only the value of the userid field is submitted, and only the necessary components that need to process the userid field are processed in the JSF lifecycle To clarify your understanding of partial submits, processing, and rendering, compare the full submit lifecycle, shown in Figure 12-1, with the partial submit lifecycle shown in Figure 12-2 Figures 12-1 and 12-2 illustrate the basic principle underlying the way Ajax is supported in the JSF standard: Ajax is just a way to take action on discrete subtrees of a complete server-side view While this is not the only way to use JSF and Ajax, it is the only way supported by the standard and therefore is the easiest way to use JSF and Ajax More advanced JSF and Ajax usage is possible, and examples abound on the Internet For example, Direct Web Remoting (DWR) is a popular Ajax framework that has some extension points for using it with JSF More on DWR can be found at http://directwebremotingorg/ Finally, no discussion on JSF and Ajax would be complete without a reference to http://jsfmatrixnet/ This site is a table of all the JSF+Ajax frameworks in existence, most of which are suitable for use with JSF 12, and therefore most of which don t use the new Ajax support in the JSF standard as of JSF 20 Now that you have a basic understanding of Ajax in the JSF standard, let s take a quick look under the covers to see how the preceding JSFReg example actually works Once we have traversed the inner workings of this demo, I will explain the full details and usage of the <f:ajax> tag and the underlying jsfajax JavaScript object on top of which this tag is built
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