Tuesday 29 March 2016

JSP ACTION TAGS

There are many JSP action tags or elements. Each JSP action tag is used to perform some specific tasks.
The action tags are used to control the flow between pages and to use Java Bean. The Jsp action tags are given below.
JSP Action Tags
Description
jsp:forward
forwards the request and response to another resource.
jsp:include
includes another resource.
jsp:useBean
creates or locates bean object.
jsp:setProperty
sets the value of property in bean object.
jsp:getProperty
prints the value of property of the bean.
jsp:plugin
embeds another components such as applet.
jsp:param
sets the parameter value. It is used in forward and include mostly.
jsp:fallback
can be used to print the message if plugin is working. It is used in jsp:plugin.
The jsp:useBean, jsp:setProperty and jsp:getProperty tags are used for bean development. So we will see these tags in bean developement.

jsp:forward action tag

The jsp:forward action tag is used to forward the request to another resource it may be jsp, html or another resource.

Syntax of jsp:forward action tag without parameter


  1. <jsp:forward page="relativeURL | <%= expression %>" />  

Syntax of jsp:forward action tag with parameter


  1. <jsp:forward page="relativeURL | <%= expression %>">  
  2. <jsp:param name="parametername" value="parametervalue | <%=expression%>" />  
  3. </jsp:forward>  

Example of jsp:forward action tag without parameter

In this example, we are simply forwarding the request to the printdate.jsp file.

index.jsp


  1. <html>  
  2. <body>  
  3. <h2>this is index page</h2>  
  4.   
  5. <jsp:forward page="printdate.jsp" />  
  6. </body>  
  7. </html>  

printdate.jsp


  1. <html>  
  2. <body>  
  3. <% out.print("Today is:"+java.util.Calendar.getInstance().getTime()); %>  
  4. </body>  
  5. </html>  

Example of jsp:forward action tag with parameter

In this example, we are forwarding the request to the printdate.jsp file with parameter and printdate.jsp file prints the parameter value with date and time.

index.jsp


  1. <html>  
  2. <body>  
  3. <h2>this is index page</h2>  
  4.   
  5. <jsp:forward page="printdate.jsp" >  
  6. <jsp:param name="name" value="javatpoint.com" />  
  7. </jsp:forward>  
  8.   
  9. </body>  
  10. </html>  

printdate.jsp


  1. <html>  
  2. <body>  
  3.   
  4. <% out.print("Today is:"+java.util.Calendar.getInstance().getTime()); %>  
  5. <%= request.getParameter("name") %>  
  6.   
  7. </body>  
  8. </html>  

jsp:include action tag

The jsp:include action tag is used to include the content of another resource it may be jsp, html or servlet.
The jsp include action tag includes the resource at request time so it is better for dynamic pages because there might be changes in future.
The jsp:include tag can be used to include static as well as dynamic pages.

Advantage of jsp:include action tag

Code reusability : We can use a page many times such as including header and footer pages in all pages. So it saves a lot of time.

Difference between jsp include directive and include action

JSP include directive
JSP include action
includes resource at translation time.
includes resource at request time.
better for static pages.
better for dynamic pages.
includes the original content in the generated servlet.
calls the include method.

Syntax of jsp:include action tag without parameter


  1. <jsp:include page="relativeURL | <%= expression %>" />  

Syntax of jsp:include action tag with parameter


  1. <jsp:include page="relativeURL | <%= expression %>">  
  2. <jsp:param name="parametername" value="parametervalue | <%=expression%>" />  
  3. </jsp:include>  

Example of jsp:include action tag without parameter

In this example, index.jsp file includes the content of the printdate.jsp file.
File: index.jsp

  1. <h2>this is index page</h2>  
  2.   
  3. <jsp:include page="printdate.jsp" />  
  4.   
  5. <h2>end section of index page</h2>  
File: printdate.jsp

  1. <% out.print("Today is:"+java.util.Calendar.getInstance().getTime()); %> 

Java Bean

A Java Bean is a java class that should follow following conventions:
  • It should have a no-arg constructor.
  • It should be Serializable.
  • It should provide methods to set and get the values of the properties, known as getter and setter methods.

Why use Java Bean?

According to Java white paper, it is a reusable software component. A bean encapsulates many objects into one object, so we can access this object from multiple places. Moreover, it provides the easy maintenance.

Simple example of java bean class


  1. //Employee.java  
  2.   
  3. package mypack;  
  4. public class Employee implements java.io.Serializable{  
  5. private int id;  
  6. private String name;  
  7.   
  8. public Employee(){}  
  9.   
  10. public void setId(int id){this.id=id;}  
  11.   
  12. public int getId(){return id;}  
  13.   
  14. public void setName(String name){this.name=name;}  
  15.   
  16. public String getName(){return name;}  
  17.   
  18. }  

How to access the java bean class?

To access the java bean class, we should use getter and setter methods.

  1. package mypack;  
  2. public class Test{  
  3. public static void main(String args[]){  
  4.   
  5. Employee e=new Employee();//object is created  
  6.   
  7. e.setName("Arjun");//setting value to the object  
  8.   
  9. System.out.println(e.getName());  
  10.   
  11. }}  
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