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marți, 3 martie 2015

Use OmniFaces MethodParam tag handler to pass a method expression as attribute into a custom tag

In this post, we will write a simple login custom tag. The climax will consist in passing a method expression as attribute into our tag using OmniFaces, <o:methodParam>. But, first let's see the implementation of our custom tag (login.xhtml):

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html"
      xmlns:ui="http://java.sun.com/jsf/facelets"
<h:body>            
  <ui:composition>
   <h:form>
    <h:panelGrid columns="2">
     <h:outputLabel for="emailId" value="#{emaillabel}"/>
     <h:inputText id="emailId" value="#{emailfield}"/>
     <h:outputLabel for="passId" value="#{passlabel}"/>
     <h:inputSecret id="passId" value="#{passfield}"/>                   
     <h:commandButton value="#{btnlabel}"/>
    </h:panelGrid>
   </h:form>
  </ui:composition>
 </h:body>
</html>

After we configure this implementation in a *.taglib.xml file, we can easily use it as below:

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html"
      xmlns:mt="http://jsf.custom/tags">
 <h:head>
  <title>               
  </title>             
 </h:head>
 <h:body>               
  <mt:login emaillabel="E-mail" passlabel="Password" btnlabel="Login" 
            emailfield="#{loginBean.email}" passfield="#{loginBean.password}"/>          
 </h:body>
</html>

Now, when we press the Login button we want to submit the form and invoke a bean method named, login(). This method will check the user credentials and return a new page, welcome.xhtml. But, by default we can submit the form but we cannot invoke the bean method, because we cannot pass a method expression as attribute into our tag (or any other Facelets tag). This is the point where OmniFaces comes to "rescue" the situation, by providing a custom tag handler that facilitate us to accomplish such tasks. This tag handler is named MethodParam, and it can be used via <o:methodParam> tag. First we add <o:methodParam> in login.xhtml, as below:

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:o="http://omnifaces.org/ui">  
 <h:body>            
  <ui:composition>
   <h:form>
    <h:panelGrid columns="2">
     <h:outputLabel for="emailId" value="#{emaillabel}"/>
     <h:inputText id="emailId" value="#{emailfield}"/>
     <h:outputLabel for="passId" value="#{passlabel}"/>
     <h:inputSecret id="passId" value="#{passfield}"/>
     <o:methodParam name="method" value="#{action}" />
     <h:commandButton value="#{btnlabel}" action="#{method}"/>
    </h:panelGrid>
   </h:form>
  </ui:composition>
 </h:body>
</html>

Perfect! Now, we just instruct JSF about our bean method as below:

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html"
      xmlns:mt="http://jsf.custom/tags">
 <h:head>
  <title>               
  </title>             
 </h:head>
 <h:body>               
  <mt:login emaillabel="E-mail" passlabel="Password" btnlabel="Login" emailfield="#{loginBean.email}" 
            passfield="#{loginBean.password}" action="#{loginBean.login()}"/>          
 </h:body>
</html>

Complete code on GitHub.

Note MethodParam can be used to pass a method expression as attribute into our tag and the method can be:

·         a method with zero arguments
·         a method with zero arguments but explicit parenthesis
·         a method with 1 view provided argument
·         a method to second bean with 1 view provided argument
·         a listener method with zero arguments
·         a listener method with zero arguments but explicit parenthesis
·         a listener method with 1 view provided argument
·         a listener method with declared event parameter, no provided arguments
·         a direct binding (no method passing) with zero arguments

So, do not hesitate to check the MethodParam Showcase to see more useful examples.

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