JSP Implicit Object in jsp

Jsp-implicit object

Introduction:

                        Implicit object means pre-defined object. Jsp provide some implicit object. Already jsp developer has created some object for later use. This object is called implicit object.

What is oops?

Object Oriented Programming is main feature of java. In java every task is performed within the method. The method is defined within the class. To call this method, using object. So we must create object of this class and use new operator to create object. Using object, we call method. So it is called object oriented programming.

A). Create class

B). Create method

C). Create object in main class

D). Using object, call the method.

But java developer feels that some object are needed often. So they created class and created object themselves. So we don’t need to create object separately. We just use object name.method name. Here we keep it in mind which method is used for which purpose.

Note:

            How to call pre defined method?

All predefined method are included within the class. And that class also is included into the package. So we import the package and create the object of the class. Using created object, we can call the method.

For example, we want to get the time. First we import java.util package. Because the method getHours() is included in java.util package. So we include java.util package and create the object for Date class.

Java.util.Date

getHours()

import java.util.*;

class Example

{

            public void display()

{

                        Date d=new Date();

                        System.out.println(d.getHours());

}

}

class Examplemain

{

            public static void main(String args[])

            {

                        Example e=new Example();

                        e.display();

            }

}

Here we import java.util and create object for Date class and using object of the Date class to call the getHours() method.

But if we use predefined boject, there is no need to create object to call method.

They defined eight pre defined object.

1). request

2). response

3). session

4). out

5). application

6). config

7). pageContext

8). page

                                                     

Implicit Object	type
request	javax.servlet.http.HttpServletRequest(For Http) javax.servlet.ServletRequest(Not Http)
It is used to retrieve data submitted along with a request.

       

                                   

Implicit Object	type
response	javax.servlet.http.HttpServletResponse(For Http) javax.servlet.ServletResponse(Not Http)
It is used to send an HTML output to the client.

Implicit Object	type
session	javax.servlet.http.HttpSession
·       session object is associated with request object.

Implicit Object	type
out	javax.servlet.jsp.JspWriter
·       Used for writing data to the output buffer ·       Buffer size can be adjusted or can be turned off using buffer attribute in page directive ·       out object is used in scriptlets

Implicit Object	type
exception	java.lang.Throwable
·       refer to the runtime exception

Implicit Object	type
page	java.lang.Object
Represent the this object for the current instance of the jsp

Implicit Object	type
pageContext	Javax.servlet.jsp.PageContext
·       represent the PageContext object for this page.

Implicit Object	type
config	Javax.servlet.ServletConfig
·       Contain servlet configuration data

 

Implicit Object	type
application	javax.servlet.ServletContext
·        It is used to share information among all usrs of a currently active application

JSP- Custom Tag- Body with Attributes

JSP- Custom Tag- Body with Attributes

Introduction:

From Previous post, we have understood how to create custom body tag. From this post, we will learn how to create custom tag with body and attributes. If we create attribute, we will add attribute name when we create tag Handler class.

Procedure:

Step 1:

            Create Project CustomTagProject.

Step 2:

            Create TLD file named as ABody.tld

Successfully Abody.tld file created.

 

Step 3:

            Create Tag handler Class named as Abody

1). Put Tag Handler name i.e. class name as Abody

2). BodyTagSupport in Tag Support Class to Extend

Click Next

1). Select TLD file.

2). Body Content as JSP

3) To add attribute.

               Click New

                        Add New Attribute window will open.

                        Where you give Attribute name as username

                        And select Attribute Type as java.lang.String

            Select required attribute checkbox

Successfully Tag Handler class file created.

 

Step 4:

            Made some changes in ABody.java

package javaclass;

import java.io.IOException;

import javax.servlet.jsp.JspException;

import javax.servlet.jsp.JspWriter;

import javax.servlet.jsp.tagext.BodyContent;

import javax.servlet.jsp.tagext.BodyTagSupport;

public class ABody extends BodyTagSupport

{

    private String username;

    public String getUsername()

    {

        return username;

    }

    public void setUsername(String username)

    {

        this.username = username;

    }

    public int doAfterBody()throws JspException

    {

        try

        {

            BodyContent bc=getBodyContent();

            String body=bc.getString();

            JspWriter out=bc.getEnclosingWriter();

            out.println(getUsername().toUpperCase());

            out.println(body.toUpperCase());

        }

        catch(Exception e)

        {

        }

        return SKIP_BODY;

    }

}

Step 5:

            Create jsp file named as ABody.jsp

Step 6:

Run the jsp file named ABody

Step 7:

Output

Structure of the CustomTagProject

JSP- Custom Tag- Body with Attributes

JSP- Custom Tag- Body with Attributes

Introduction:

From Previous post, we have understood how to create custom body tag. From this post, we will learn how to create custom tag with body and attributes. If we create attribute, we will add attribute name when we create tag Handler class.

Procedure:

Step 1:

            Create Project CustomTagProject.

Step 2:

            Create TLD file named as ABody.tld

JSP Custom Tag with Body

JSP- Custom Tag with Body

Introduction:

Custom tags include jsp components such as text, jsp scriptlets, jsp expression within its body tag are called custom tags with body.

< good:GoodMorning >
suresh goodmoring
< /good:GoodMorning >

The output is the body content is converted into the UpperCase.

We specify custom tag contain body when we are creating TLD file. When we create TLD file, we specify < body-content > element of the TLD as JSP. When we create Custom Tag .we specify < body-content > as empty. Now we are going to create custom tag with body so we specify < body-content > as JSP to indicate that container evaluate the body content of the tag.




Note:
We specify < body-content > as tagdependent, the jsp container should not evaluate the body of the tag but instead pass it to the tag handler for evaluation.



Problem:

< good:GoodMorning >
suresh goodmoring
< /good:GoodMorning >

The output is the body content is converted into the UpperCase.

Procedure:

Step 1:

Create Project named as CustomTagProject (Already we have Created CustomTagProject)

If you are new to Custom Tag, Please refer Custom tag Empty Tag Creation.

Custom Tag – Example For Empty Tag

Step 2:

Create TLD file. Named good.tld

How to create TLD, please refer 

Important:

No need to include coding into the TLD file. The content of the TLD file will be automatically included into the TLD file when we create Tag handler Class.

Step 3:

            Create Tag Handler Class named as GoodMorning.

Select BodyTagSupport because we are going to create Custom tag with body.

Note: we have selected Body Content as JSP.

Step 4:

            Create jsp file named as good.jsp.

< %@page contentType="text/html" pageEncoding="UTF-8"% >
< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
http://www.w3.org/TR/html4/loose.dtd >
< %@taglib uri="/WEB-INF/tlds/good" prefix="good" % >
< html >
< head >
< title > JSP good Page < /title >
< /head >
< body >
< h1 > Hello World! < /h1 >
< good:GoodMorning >
sureshkumar
< /good:GoodMorning >
< /body >
< /html >

Step 5:

            Run the good.jsp

Step 6:

            Get Output

Step 7:

            Structure of the CustomTagProject

JSP- Custom Tag with Attributes

Introduction:

                       Custom tag contains many attributes. For every attribute of custom tag, we need to create a property. We use getXXX() and setXXX() methods to access and set the value for the property in the Tag handler Class.

                       Example:

< hello:Hello username=”sureshkumar”/ >

                      

                       

Here, username is a property of the custom tag. And the value of the username is sureshkumar.

Let us go to create custom tag with attributes.

We use TagSupport class to implement custom tag with attributes.

We include username attributes into the Tag Handler Class.

We also setXXX() for username as setUsername().

We also getXXX() for username as getUsername().

To define a custom tag with attribute in a TLD file, we need to specify that the custom tags contain attributes in the attribute elements of the TLD file. The attribute elemtn contains the following sub-elements.

name: specify the name of the attribute.

required: specify that the attribute is required or optional. If you specify required as true,the attribute value must be present in the JSP page.

rtexprvalue:specify that run-time expression, for example JSP expression can be used for this attribute. Possible  values include true,false,yes,no.

Procedure:

Step 1:

            Create project (Already we have create project named as CustomTagProject)

            You want to know how to create Project to develop the jsp page.
            Refer Following Link

Create Custom Tag – Empty Tag Example

Step 2:

            Create TLD file. Named hello.tld

Step 3:

Create Tag Handler Class named as Hello

Already we have created Welcome Tag Handler Class in creating Empty custom tag example. Follow same steps to create Tag Handler Class.

Below display window is a Tag Handler window. Where you give Tag Handler class name such as Hello.

Tag Support Class to Extend:

Select SimpleTagSupport

Next

Below display window is a New File window, where you select TLD file.

Select Body content as Empty.

Add attributes from here

Click New button right side of the Attribute.

Below window display

OK

 Finish. Tag Handler named Hello will be successfully created.

Note: Made some changes in Hello.java.

Extends TagSupport class.

Add doStartTag() and doEndTag()

Hello.java

package javaclass;

import javax.servlet.jsp.JspWriter;

import javax.servlet.jsp.JspException;

import javax.servlet.jsp.PageContext;

import javax.servlet.jsp.tagext.JspFragment;

import javax.servlet.jsp.tagext.SimpleTagSupport;

import javax.servlet.jsp.tagext.TagSupport;

public class Hello extends TagSupport

{

    private String username;

    public String getUsername()

    {

        return username;

    }

    public void setUsername(String username)

    {

        this.username = username;

    }

    public int doStartTag() throws JspException

    {

        try

        {

           JspWriter out=pageContext.getOut();

           out.println("Welcome"+getUsername());

        }

        catch(Exception e)

        {

        }

        return SKIP_BODY;

    }

    public int doEndTag() throws JspException

    {

        return SKIP_PAGE;

    }

}

                 

Step 4:

             Create jsp file named as Hello.jsp

< %@page contentType="text/html" pageEncoding="UTF-8"% >
< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
http://www.w3.org/TR/html4/loose.dtd >
< %@taglib uri="/WEB-INF/tlds/hello" prefix="hello" % >
< html >
< head >
< title > Hello JSP Page < /title >
< /head >
< body >
< h1 > Hello World! < /h1 >
< hello:Hello username="sureshkumar"/ >
< /body >
< /html >


Step 5:

Run the Hello.jsp

Step 6:

Get Output

Structure of the CustomTagProject

JSP Custom Tag Empty Custom Tag

JSP- Custom Tag- Empty Tag.

Introduction:

                        Empty custom tag means that does not have any attributes or body.

< mytag:hello/ >

Creating Custom Tag-Empty Tag:

To create custom tag, three components need.

Ø      The tag library descriptor file that maps the XML elements to the tag implementation.

Ø      The tag handler class that defines tags behavior.

Ø      The JSP file that uses the tag library

                

Procedure:

Step 1:

                       Create Project named as CustomTagProject.

                 

Note:Already we have seen how to create the project for developing the web application.

Step 2:

Create two Folders. One for storing jsp files. Another one for storing   Tag Handler class.

Note: Already we have seen how to create Folder in the previous post. Also we have seen where to create Folder for storing jsp file and where to create Folder for storing tag handler class.

Structure of the CustomTagProject

You can save jsp file under jsp folder. And also you can save the tag handler class under javaclass Folder.

Task 1:Tag Library Descriptor file (TLD file)

First task is to identify the java class for the server and to associate it with a particular XML tag name. Let us create TLD file.

Let us see how to create TLD files.

We give TLD file name as myown-taglib.tld

Step1:

Right click on WEB-INF and select New and Other

New File window will open.

Select web under Categories

Also select Tag Library Descriptor(TLD) under File Types

 

Next

New Tag Library Descriptor window will open.

You give TLD name as welcome.tld

Also give prefix name as wel

After creaing welcome.tld. you can see welcome.tld file like below.

welcome.tld


< ?xml version="1.0" encoding="UTF-8"? >
< taglib version="2.1" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd >
< tlib-version > 1.0 < /tlib-version >
< short-name > wel < /short-name >
< uri > /WEB-INF/tlds/welcome < /uri >

< /taglib >

Task 2:Tag Handler Class

Ø      The second task is to define a java class that tells the JSP ENGINE what to do when it sees the tag.

Ø      This class must implements javax.servlet.jsp.tagext.Tag interface.

Ø      Extends TagSupport or BodyTagSupport

Let us go to create java class that display “welcome India”

Right click on javaclass. And select New and Other.

New File window will open.

Where you select web under categories

And also select Tag Handler under File types

Next

New Tag Handler window will open.

You give Tag Handler name as Welcome.

Next

New File window will open.

Where you select TLD

Browse and select TLD under WEB-INF\tlds\welcome.tld

Select Body Content: empty

Finish

Welcome.java file is successfully created.

Welcome.java

package javaclass;

import javax.servlet.jsp.JspWriter;

import javax.servlet.jsp.JspException;

import javax.servlet.jsp.tagext.JspFragment;

import javax.servlet.jsp.tagext.SimpleTagSupport;

import javax.servlet.jsp.tagext.TagSupport;

public class Welcome extends TagSupport

{

    public int doStartTag() throws JspException

    {

        try

        {

            JspWriter out=pageContext.getOut();

            out.println("Welcome India");

        }

        catch(Exception e)

        {

        }

        return SKIP_BODY;

    }

    public int doEndTag() throws JspException

    {

        return SKIP_PAGE;

    }

}

Create JSP file

Create jsp file  -- Home.jsp

Let us see how to create Home.jsp

Right click on jsp Folder.

New File window will open.

Where you select web under categories and select JSP under File Types.

Next

New JSP File window will open.

Finish

Home.jsp file is successfully created.

In Home.jsp, we include taglib directive.

How to include Taglib directive.

< %@taglib uri="/WEB-INF/tlds/welcome" prefix="wel" % >

We create jsp file. We define taglib tag to include custom tag into jsp.


Include following jsp coding into the Home.jsp

< %@taglib uri="/WEB-INF/tlds/welcome" prefix="wel" % >
< %@page contentType="text/html" pageEncoding="UTF-8"% >
< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
http://www.w3.org/TR/html4/loose.dtd >

< html >
< head >
< title > JSP Home Page < /title >
< /head >
< body >
< h1 > Hello World! < /h1 >
< wel:Welcome/ >
< /body >
< /html >


Run the Home.jsp

Right click on Home.jsp and select Run File.

You get output

Strutcture Of The CustomTagProject