USING BEANS IN JSP
Java
Beans
Java
Beans are reusable components. They are used to separate Business logic
from the Presentation logic. Internally, a bean is just an instance of a
class.
JSP’s
provide three basic tags for working with Beans.
- <jsp:useBean
id=“bean name” class=“bean class”
scope = “page | request | session |application ”/>
bean
name = the name that refers to the bean.
Bean
class = name of the java class that defines the bean.
- <jsp:setProperty
name = “id” property = “someProperty”
value = “someValue” />
id = the name of the bean as specified in the useBean tag.
property
= name of the property to be passed to the bean.
value
= value of that particular property .
An variant for this
tag is the property attribute can be replaced by an
“ * ”. What this does is that it accepts all the form
parameters and thus reduces the need for writing multiple setProperty
tags. The only consideration is that the form parameter names should be
the same as that of the bean property names.
- <jsp:getProperty
name = “id” property = “someProperty” />
Here
the property is the name of the property whose value is to be obtained
from the bean.
BEAN
SCOPES :
These defines the range and lifespan of the bean.
The different
options are :
Any
object whose scope is the page will disappear as soon as the current
page finishes generating. The object with a page scope may be modified
as often as desired within the particular page but the changes are lost
as soon as the page exists.
By
default all beans have page scope.
Any
objects created in the request scope will be available as long as the
request object is. For
example if the JSP page uses an jsp:forward tag, then the bean should be
applicable in the forwarded JSP also, if the scope defined is of Request
scope.
In
JSP terms, the data associated with the user has session scope. A
session does not correspond directly to the user; rather, it corresponds
with a particular period of time the user spends at a site. Typically,
this period is defined as all the visits a user makes to a site between
starting and existing his browser.
The
BEAN structure :
The
most basic kind of bean simply exposes a number of properties by
following a few simple rules regarding method names. The Java BEAN is
not much different from an java program. The main differences are the
signature methods being used in a bean. For passing parameters to a
bean, there has to be a corresponding get/set method for every
parameter. Together these methods are known as accessors.
Eg.
Suppose we want to pass a parameter “name” to the bean and then
return it in the capital form. In the bean, there has to be an setName()
method and an corresponding getProperty() method.
A point to be noted is that the first letter of the property name
is capitalized.(Here, N is in capital)
Also, it is possible to have either get or set in a bean,
depending on the requirement for a read only or a write only property.
An
example for a Database connection bean is as shown :
|
package
SQLBean;
import
java.sql.*;
import java.io.*;
public
class DbBean
{
String dbURL = "jdbc:db2:sample";
String dbDriver = "COM.ibm.db2.jdbc.app.DB2Driver";
private Connection dbCon;
public DbBean(){
super();
}
public boolean connect() throws
ClassNotFoundException,SQLException{
Class.forName(dbDriver);
dbCon =
DriverManager.getConnection(dbURL);
return true;
}
public void close() throws SQLException{
dbCon.close();
}
public ResultSet execSQL(String sql) throws SQLException{
Statement s = dbCon.createStatement();
ResultSet r = s.executeQuery(sql);
return (r == null) ? null : r;
}
public int updateSQL(String sql) throws SQLException{
Statement s = dbCon.createStatement();
int r = s.executeUpdate(sql);
return (r == 0) ? 0 : r;
}
}
|
The
description is as follows :
This bean is packaged in a folder called as “SQLBean”. The
name of the class file of the bean is DbBean. For this bean we
have hardcoded the Database Driver and the URL. All the statements
such as connecting to the database, fetching the driver etc are
encapsulated in the bean.
There
are two methods involved in this particular bean :
Executing
a particular query.
Updating
a database.
The
execSQL(String sql) method accepts the SQL query in the form of
a string from the JSP file in which this bean is implemented.
Then
the createStatement() method initiates the connection with the dbCon
connection object.
Further
the executeQuery(sql) method executes the query which is passed
on as a string.
return
(r == null) ? null : r ;
What
this statement does is that, if the value of r is null, it
returns a null value and if it is a non null value, it returns the value
of r. Though this statement seems redundant, it is useful for
preventing any errors that might occur due to improper value being set
in r.
The
JSP Program is as shows :
|
<HTML>
<HEAD><TITLE>DataBase
Search</TITLE></HEAD>
<BODY>
<%@
page language="Java" import="java.sql.*" %>
<jsp:useBean
id="db" scope="request" class="SQLBean.DbBean"
/>
<jsp:setProperty
name="db" property="*" />
<%!
ResultSet rs = null ;
ResultSetMetaData rsmd = null ;
int numColumns ;
int i;
%>
<center>
<h2>
Results from </h2>
<hr>
<br><br>
<table>
<%
db.connect();
try
{
rs = db.execSQL("select * from EMPLOYEE");
i
= db.updateSQL("UPDATE employee set FIRSTNME = 'hello world' where
EMPNO='000010'");
out.println(i);
}catch(SQLException
e) {
throw new ServletException("Your query is not working",
e);
}
rsmd = rs.getMetaData();
numColumns =
rsmd.getColumnCount();
for(int column=1; column <=
numColumns; column++){
out.println(rsmd.getColumnName(column));
}
%>
<%
while(rs.next())
{
%>
<%=
rs.getString("EMPNO") %>
<BR>
<%
}
%>
<BR>
<%
db.close();
%>
Done
</table>
</body>
</HTML>
|
The
corresponding tags used in the JSP are as follows :
<jsp:useBean
id="db" scope="request" class="SQLBean.DbBean"
/>
This tag specifies that
the id of this bean is “db”. This id is used throughout the page to
refer to this particular bean. The scope of this bean is limited to the
request scope only. The class attribute points to the class of the bean.
Here the class file is
stored in the SQLBean folder.
<jsp:setProperty
name="db" property="*" />
This
property is used for passing on all the values which are obtained from
the form. In this program, the SQL query can be passed on to the program
as a part of the request.getParameter so that the query can be
modified according to the requests.
rs
= db.execSQL("select * from EMPLOYEE");
We
can access the execSQL() method by using the bean id. Also the
SQL is passed on to this method.
i =
db.updateSQL("UPDATE employee set FIRSTNME = 'hello world' where
EMPNO='000010'");
The
updateSQL() method can also be used in the same JSP
program. Here we are updating the employee table and resetting the
FIRSTNME field where the EMPNO is 000010.
The
major difference between an executeQuery and executeUpdate is that, an
executeQuery returns the result set and an executeUpdate returns an
integer value corresponding to the number of rows updated by the current
query.
As
can be seen, it is very easy to connect to databases using beans rather
than writing the whole code over and over again in every JSP which
requires to talk to the database.
|
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Current Comments
14 comments so far (post your own) View All Comments Latest 10 Comments:awesome tutorial
Posted by robby fowler on Monday, 04.21.08 @ 09:45am | #57376
This is an awesome tutorial
Posted by javaseek on Wednesday, 03.19.08 @ 23:44pm | #53402
Very very comfortable material for beginners as well as for programmers.very good site. i have no words to tell about this site
Posted by nagapriya on Wednesday, 01.30.08 @ 13:43pm | #46581
hi i wanna download JSP tutorials provided by roseindia.net .Is there any lnk to download to download this tutorials .
thnnks n regards
vikam singh
Posted by vikram on Monday, 12.24.07 @ 11:31am | #43549
Try to provide me uptates about given in the titla
Posted by mukesh kumar on Thursday, 12.20.07 @ 13:33pm | #43091
USING BEANS IN JSP program how can we get Driver and url from web.xml
Posted by Ramakrishna K.V on Tuesday, 12.18.07 @ 17:04pm | #42832
this is excelent tutorials
Posted by surya on Tuesday, 10.9.07 @ 17:02pm | #32944
the tutorial is very good for the beginners...
very nice explanations have been given...
Posted by SharadhaAnanth on Friday, 10.5.07 @ 12:44pm | #31794
how to associate a bean to a text box, radio button, drop down menu .
Posted by kuldeep on Thursday, 07.26.07 @ 10:37am | #21970
It's examples are best, for those who are starting from premitive stage, and want to understand from deep.
Posted by jeet on Friday, 07.6.07 @ 12:29pm | #20822