Here is the markup that initiates the process:


<pre class="brush: xml; highlight:[4,5]">
&lt;h:form prependId="false"> 
 &lt;h:panelGrid id="panel"> 
 &lt;h:panelGroup>
 &lt;p:inputText id="email" value="#{indexBean.emailAddress}" size="30" >
 &lt;p:ajax event="blur" 
 onstart="$('#progressind').css('visibility','visible');" 
 oncomplete="$('#progressind').css('visibility','hidden');" 
 listener="#{indexBean.validateEmail}" 
 update="messages" />
 &lt;/p:inputText>
 &lt;!-- progress indicator -->
 &lt;img id="progressind" src="./images/prog.gif" width="20" 
 style="margin-left: 10px;border:0px;visibility:hidden" />
 &lt;/h:panelGroup> 

 &lt;p:watermark for="email" value="Enter email address" />
 &lt;p:inputText id="lastname" size="30" />
 &lt;p:commandButton update="messages" value="Submit" 
 actionListener="#{indexBean.process}" />

 &lt;p:messages id="messages" showDetail="true" showSummary="true" 
 closable="true" />
 &lt;/h:panelGrid>
&lt;/h:form> 
</pre>


The validation is handled from by &lt;p:ajax /> blur event handler which is listened to by validateEmail bean method.&nbsp;&nbsp;In the snippet above,&nbsp;we a have progress visual indicator that shows up while the validation is on going.



In this example,&nbsp;the actual validation is a two step process.&nbsp;&nbsp;The submitted email address is compared against a regular expression pattern for validity of just the format,&nbsp;and then the domain name is checked for its existence and presence of mail exchanger in the domain through DNS lookup.&nbsp;&nbsp;See comments in the code below.



<pre class="brush: java">
package {package-name};

import java.util.Hashtable;
import javax.faces.application.FacesMessage;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.faces.context.FacesContext;
import javax.faces.event.ActionEvent;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;

@ManagedBean
@SessionScoped
public class IndexBean implements java.io.Serializable {

 public IndexBean() {
 }
 String emailAddress;

 public void setEmailAddress(String s) {
 emailAddress = s;
 }

 public String getEmailAddress() {
 return emailAddress;
 }

 public void validateEmail() {
 String email = getEmailAddress();
 if (!isValid(email)) {
 FacesContext.getCurrentInstance().addMessage(null,
 new FacesMessage(FacesMessage.SEVERITY_ERROR, "Error",
 email + " is not a valid email address"));

 }
 }

 boolean isValid(String email) {

 // Reqular expression pattern to validate the format submitted
 String validator = "^[_a-zA-Z0-9-]+(\\.[_a-zA-Z0-9-]+)*@[a-zA-Z0-9-]+"
 + "(\\.[a-zA-Z0-9-]+)*(\\.[a-zA-Z]{2,})$";

 if (!email.matches(validator)) {
 return false;
 }

 // Split the user and the domain name
 String[] parts = email.split("@");

 boolean retval=true;
 // This is similar to nslookup –q=mx domain_name.com to query
 // the mail exchanger of the domain.
 try {
 Hashtable&lt;String, String> env = new Hashtable&lt;String, String>();
 env.put("java.naming.factory.initial",
 "com.sun.jndi.dns.DnsContextFactory");
 DirContext context = new InitialDirContext(env);
 Attributes attributes =
 context.getAttributes(parts[1], new String[]{"MX"});
 Attribute attribute = attributes.get("MX");
 if (attribute.size() == 0) {
 retval=false;
 }
 context.close();
 return retval;

 } catch (Exception exception) {
 return false;
 } 
 }

 public void process(ActionEvent event) { 
 // Validate again 
 String email = getEmailAddress();
 if (!isValid(email)) {
 FacesContext.getCurrentInstance().addMessage(null,
 new FacesMessage(FacesMessage.SEVERITY_ERROR, "Error",
 email + " is not a valid email address"));
 return;

 }
 
 // The task;
 }
}

</pre>



Our regular expression pattern will match an address with dot and hyphen in the user name with 2 characters or more extension in the domain name.&nbsp;&nbsp; It is also not case sensitive.



That's it Good Luck.

Validating an email address in PrimeFaces p:inputText field with p:ajax