Logic Empty Tag (<logic:empty>...</logic:empty>)
empty tag - If the requested variable is either null or an empty
string then we use this tag to evaluate the contents contained in the nested
body parts of this
tag.
Tag evaluation of the nested body content occurs only if the specified value is
either absent (i.e. null), an empty string (i.e. a java.lang.String
with a length of zero), or an empty java.util.Collection or java.util.Map
(tested by the isEmpty() method on the respective interface).
Attributes of Empty Tag
| Attribute Name |
Description |
| name |
This attribute specifies a JSP bean
variable which is required to make comparison.
|
| property |
The variable contains the property
of the bean which is required to make comparison and is specified
by the name attribute.
|
| scope |
This specifies the bean scope within which
the bean
is searched by the name
property, or "any scope" if not specified.
|
Logic notEmpty Tag (<logic:notEmpty>...</logic:notEmpty>)
notEmpty
- If the requested variable is neither null nor an empty
string then we use this tag to evaluate the contents contained in the nested
body parts of this
tag.
Tag evaluation of the nested body content occurs only if the specified value is
available (i.e.not null) and is not an empty string (i.e. a java.lang.String
with a length of zero).
Attributes of notEmpty Tag
| Attribute Name |
Description |
| name |
This attribute specifies a JSP bean
variable which is required to make comparison.
|
| property |
The variable contains the property
of the bean which is required to make comparison and is specified
by the name attribute.
|
| scope |
This specifies the bean scope within which the bean
is searched by the name
property, or "any scope" if not specified.
|
Example Illustrating the use of the Empty<logic:empty>
and the notEmpty <logic:notEmpty> logic tags.
Here you will learn to use the Struts Logic tags.
We will cover an example that will show a comparison between the two
logic tags (ie..<logic:empty> and the <logic:notEmpty>).
Example code
Creating an Action
Class
Develop a simple action class EmptyAction.java.
package roseindia.net;
import java.io.*;
import java.util.*;
/**
* @author Amit Gupta
* @Web http://www.roseindia.net
* @Email struts@roseindia.net
**/
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
import org.apache.struts.action.*;
public class EmptyAction extends Action
{
public ActionForward execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
return mapping.findForward("success");
}
}
|
|
Creating Form Bean
Our form bean class contains only one property text.
Here is the code of FormBean (EmptyForm.java)
package roseindia.net;
import org.apache.struts.action.*;
/**
* @author Amit Gupta
* @Web http://www.roseindia.net
* @Email struts@roseindia.net
**/
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class EmptyForm extends ActionForm
{
private String text = "";
public String getText()
{
return text;
}
public void setText(String text)
{
this.text=text;
}
}
|
|
Defining form Bean in struts-config.xml file
Add the following entry in the struts-config.xml file
for defining the form bean
| <form-bean name="EmptyForm" type="roseindia.net.EmptyForm"/> |
Developing the Action Mapping in the struts-config.xml
Here, Action mapping helps to select the method from the Action class for specific
requests.
<action path="/EmptyAction"
type="roseindia.net.EmptyAction"
name="EmptyForm"
scope="request"
input="/pages/input.jsp">
<forward name="success" path="/pages/output.jsp"/>
</action> |
Developing the input.jsp page
<%@ taglib uri="/tags/struts-html" prefix="html" %>
<%@ taglib uri="/tags/struts-logic" prefix="logic" %>
<html:html>
<head>
<title>Using <logic> Tags</title>
</head>
<body>
<h1>Using <logic> Tags</h1>
<html:form action="/EmptyAction" method ="post">
<h2>Enter your name:</h2>
<html:text property="text"/>
<br>
<br>
<html:submit value="Submit"/>
<html:cancel/>
</html:form>
</body>
</html:html>
|
Developing the output.jsp page
<%@ taglib uri="/tags/struts-bean" prefix="bean" %>
<%@ taglib uri="/tags/struts-logic" prefix="logic" %>
<HTML>
<HEAD>
<TITLE>Here's Your Data...</TITLE>
</HEAD>
<BODY>
<H3>Here's Your Data...</H3>
<h4>The text field text:</h4>
<bean:write name="EmptyForm" property="text"/>
<logic:notEmpty name="EmptyForm" property="text" scope="request">
<h4>Using the tag <logic:notEmpty > </h4>
Results:not Empty
</logic:notEmpty>
<logic:empty name="EmptyForm" property="text" scope="request">
<h4>Using the tag<logic:empty ></h4>
Results: Empty
</logic:empty>
</BODY>
</HTML>
|
Add the following line in the index.jsp to call the
form.
<li>
<html:link page="/pages/input.jsp">Struts File Upload</html:link>
<br>
Example demonstrates how EmptyAction Class works.
</li>
Building and Testing the Example
To build and deploy the application go to Struts\Strutstutorial
directory and type ant on the command prompt. This will deploy the application.
Open the browser and navigate to the input.jsp page.
Your browser displays the following page.
Writing nothing to the out.jsp
page displays the
working of the Empty Logic tag <logic:empty >
Writing nothing displays
the following out.jsp page
Now write any data to the input.jsp
to see the working of the notEmpty logic tag <logic:notEmpty
>
The <logic:notEmpty >
evaluated here displays the output.jsp
as
|
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