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

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

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.

Creating Form Bean

Our form bean class contains only one property text. Here is the code of FormBean (EmptyForm.java)

Defining form Bean in struts-config.xml file

Add the following entry in the struts-config.xml file for defining the form bean

 Developing the Action Mapping in the struts-config.xml

Here, Action mapping helps to select the method from the Action class for specific requests.

Developing the input.jsp page

Developing the output.jsp page

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

Struts logic tags are conditional tags that replaces scriptlets in the jsp files.

This tag library contains tags that do the following things :
    conditional generation of the output text,
    generate iterations to output the text,
    application flow management,
    matching strings and substrings…

Logic tags available in the Struts Framework

Struts logic tags uses equal, greaterEqual, greaterThan, lessEqual, lessThan, notEqual tags to compare the values. There are rules that must be  followed :

• Initially the specified variable needed to be compared is examined (whether it can be converted to a double or to a long). Then a  numeric (either floating point or integer) type comparison is done. If numeric conversion fails than a String comparison is performed.
  
• The variable to be compared is retrieved from the request attribute(s)  that may be a cookie, header, name, parameter or property available to the specified tag. This variable is then converted to the appropriate type needed for the comparison..
  
• If the variable or property to be compared returns null, it is converted into a zero-length string before the comparison occurs.
  
• If the comparison logic returns a true value then only the specific comparison is performed and subsequently the nested body content is evaluated .

Struts logic tags  can also do the substring matching using the tags (match, notMatch). There are rules that must be  followed :

• The variable to be compared is retrieved from the request attribute(s)  that may be a cookie, header, name, parameter or property available on this tag. Then this variable is converted to a String, if necessary.
  
• If the retrieval of the variable fails or it contains a null value then a request time exception is thrown.  
  
• The existence of the variable as a substring is examined at the position specified by the location attribute Location can be specified at the beginning (if location is set to start), at the end (if location is set to end), or anywhere (if location is not specified).

A JspException is thrown at runtime if any tag is utilized incorrectly or any invalid combination of tag attributes are used. To process the actual exception that caused the problem,  a request attribute under key org.apache.struts.action.EXCEPTION  is passed to the error page.

In the subsequent section we will show you the examples of these tags.

Struts Logic Tags examples.

1. Introduction to Struts Logic Tags
   Struts logic tags are conditional tags that replaces scriptlets in the jsp files.
    
   
2. Logic Empty and notEmpty Tags
   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)
     
   
3. Logic Equal and notEqual Tags
   if the requested variable is equal to the specified value then this tag is used to evaluate the contents contained in the nested body parts of this tag
     
   
4. Logic greaterEqual and greaterThan Tags
   This tag compares the variable against the specified constant value. If the variable is greater than or equal to the specified value then the nested body contents of this tag is evaluated
     
   
5. Logic lessEqual and lessThan Tags
   This tag compares the variable against the specified constant value. If the variable is less than or equal to the specified value then the nested body contents of this tag is evaluated
     
   
6. Logic match and notMatch Tags
   This tag matches the variable specified as a String against the specified constant value. If the value is a substring  then the nested body content of this tag is evaluated.
     
   
7. Logic present and notPresent Tags
   This tag checks the current request and depending on which attribute is specified, it evaluates the nested body content of this tag only if the specified value is present.
   

The tag library 忛ested?is included in Struts 1.1. In this tutorial we are going to explain what are the features of nested tag library and how you can use it. We can manage nested beans easily with the help of struts nested tag library. 

Nested tags are used in the nested context. The Nested tags and its supporting classes extends the base struts tags and making them possible to relate to each other in the nested fashion. In case of Nested tags the original logic of the tags does not change and all the references to beans and bean properties is managed in the nested context.

As far as bean is concerned, one is associated with another internally and access to all the beans are  through the current one. The beans that refers to another is the parent and the second related to the first one is its child. Here both ‘parent’ and ‘child’ denotes a hierarchical structure of beans. 
    
For example, Take an object which represents a Author. Each author  related to many book  .If this case was translated to bean objects, 
the author object would have a reference to the book objects he wrote, and each bunch object would hold a reference to
the chapters in the books.

The author object is the parent to the books object, and the books object is a child of the author object. The books object
is parent to its child chapters objects, and the child chapters objects children of the books object. The author is higher in
the hierarchy than the books, and the chapters lower in the hierarchy to the books.

package roseindia.web.common;

public class Books {

	private int id;

	private String name;
	//constructors

	public Books(){}
	public Books(int id, String name){

		this.id = id;

		this.name = name;

	}

	public int getId() {

		return id;

	}

	public void setId(int id) {

		this.id = id;

	}

	public String getName() {

		return name;

	}

	public void setName(String name) {

		this.name = name;

	}

}

package roseindia.web.common;

import java.util.*;

public class Authors {

	

	private int id;

	private String name;

	

	//books collection

	private Collection books;

	

	//constructors

	public Authors() {}

	public Authors(int id, String name, Collection books){

		this.id = id;

		this.name = name;

		this.books = books;

	}

	public Collection getBooks() {

		return books;

	}

	public void setBooks(Collection books) {

		this.books = books;

	}

	public int getId() {

		return id;

	}

	public void setId(int id) {

		this.id = id;

	}

	public String getName() {

		return name;

	}

	public void setName(String name) {

		this.name = name;

	}

}

package roseindia.web.struts.form;

import java.util.*;

import org.apache.struts.action.ActionForm;

import org.apache.struts.action.ActionMapping;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import roseindia.web.common.Authors;

import roseindia.web.common.Books;

public class AuthorsBooksForm extends ActionForm {

	Authors authors;

	public void setAuthors(Authors authors) {

		this.authors = authors;

	}

	public Authors getAuthors() {

		return authors;

	}

	

	public void reset(ActionMapping mapping,HttpServletRequest request) {

		

		//initial a dummy collection of books

		Collection books = new ArrayList();

		

		books.add(new Books(1, “Teach Yourself C++”));

		books.add(new Books(2, “Java: The Complete Reference, J2SE”));

		books.add(new Books(3, “Struts: The Complete Reference”));

		//initial a dummy authors

		authors = new Authors(1, “Herbert Schildt”, books);

		

	}

}

package roseindia.web.struts.action;

import roseindia.web.struts.form.AuthorsBooksForm;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.util.*;

import org.apache.struts.action.Action;

import org.apache.struts.action.ActionForm;

import org.apache.struts.action.ActionForward;

import org.apache.struts.action.ActionMapping;

public class AuthorsBooksAction extends Action {

	

	public ActionForward execute(

		ActionMapping mapping,

		ActionForm form,

		HttpServletRequest request,

		HttpServletResponse response) {

		AuthorsBooksForm booksForm = (AuthorsBooksForm) form;

		

		return mapping.findForward(“books”);

	}

}

<%@ page language=”java”%>

<%@ taglib uri=”/tags/struts-bean” prefix=”bean” %>

<%@ taglib uri=”/tags/struts-html” prefix=”html” %>

<%@ taglib uri=”/tags/struts-logic” prefix=”logic” %>

<%@ taglib uri=”/tags/struts-nested” prefix=”nested”%>

 

<html>

	<head>

		<title>Struts nested tag Example</title>

	</head>

	<body>

	  <h1>Struts nested tag Example</h1>

	  <b>Author and his books:</b>

		<html:form action=”/example” method=”post”> 

			<nested:nest property=”authors”>

				

				<b><nested:write property=”name”/> </b>

				<nested:iterate property=”books”>

						

					<ul><li><nested:write property=”name”/></li></ul>

				</nested:iterate>

			</nested:nest>

			

		</html:form>

	</body>

</html>

 <form-beans>

  	<form-bean name=”AuthorsBooksForm”

		 type=”roseindia.web.struts.form.AuthorsBooksForm” />

 </form-beans>

<action-mappings>

         <action

            path=”/example”

            type=”roseindia.web.struts.action.AuthorsBooksAction”

            input=”/pages/user/authorsbooks.jsp”

            name=”AuthorsBooksForm”

            scope=”request”

            validate=”false”>

            <forward name=”example” path=”/pages/user/authorsbooks.jsp” />

        </action>

</action-mappings>

This tutorial shows you how you can configure Struts DataSource Manager on the Tomcat 5.5.9 server. We will use struts 1.2.7 in this tutorial. In this tutorial we will configure Struts DataSource Manager to use MySQL Database and use the connection provided by Struts DataSource in action class.

Downloading and Installing Tomcat 5.5.9
Download jakarta-tomcat-5.5.9 from http://jakarta.apache.org/tomcat/. Install it on your machine. Run and test the pages that comes with the tomcat.

Download Struts
Download Struts struts-1.2.7 from http://struts.apache.org/download.cgi and unzip it to your favorite directory. Go to the struts-1.2.7\webapps directory and then unzip struts-blank.war file. We will use this file to write our tutorial.

Download MySQL JDBC Driver
Download mysql-connector-java-3.0.16-ga-bin.jar from here mysql-connector-java-3.0.16-ga-bin.jar or you can download and use the latest version of mysql jdbc driver. Copy the JDBC driver file (mysql-connector-java-3.0.16-ga-bin.jar or latest version) to the jakarta-tomcat-5.5.9\common\lib directory of your tomcat installation. This will add the MySQL JDBC driver to the tomcat server.

Creating MySQL Database
In this tutorial I am using MySQL server installed on my local machine. You can download and install MySQL on your local machine and use for this tutorial. If you already have MySQL server then you can use the existing MySQL server.

Create database “strutsdatabase” on the MySQL server and then run the following query to create test table.

<data-sources>

<data-source type=”org.apache.tomcat.dbcp.dbcp.BasicDataSource“>

    <set-property

      property=”driverClassName”

      value=”com.mysql.jdbc.Driver” />

    <set-property

      property=”url”

      value=”jdbc:mysql://localhost:3306/strutsdatabase?autoReconnect=true” />

    <set-property

      property=”username”

      value=”root” />

    <set-property

      property=”password”

      value=”” />

    <set-property

      property=”maxActive”

      value=”10″ />

    <set-property

      property=”maxWait”

      value=”5000″ />

    <set-property

      property=”defaultAutoCommit”

      value=”false” />

    <set-property

      property=”defaultReadOnly”

      value=”false” />

    <set-property

      property=”validationQuery”

      value=”SELECT COUNT(*) FROM test” />

</data-source>

</data-sources>