Acessing data from DataBase into Jsp?
>> Wednesday, June 15, 2011
<%@ page language="java" import="java.sql.*" %>
<%
String driver = "org.gjt.mm.mysql.Driver";
Class.forName(driver).newInstance();
Connection con=null;
ResultSet rst=null;
Statement stmt=null;
try{
String url="jdbc:mysql://localhost/books?user=
<user>&password=<password>";
con=DriverManager.getConnection(url);
stmt=con.createStatement();
}
catch(Exception e){
System.out.println(e.getMessage());
}
if(request.getParameter("action") != null){
String bookname=request.getParameter("bookname");
String author=request.getParameter("author");
stmt.executeUpdate("insert into books_details(book_name,
author) values('"+bookname+"','"+author+"')");
rst=stmt.executeQuery("select * from books_details");
%>
<html>
<body>
<center>
<h2>Books List</h2>
<table border="1" cellspacing="0" cellpadding
="0">
<tr>
<td><b>S.No</b></td>
<td><b>Book Name</b></td>
<td><b>Author</.b></td>
</tr>
<%
int no=1;
while(rst.next()){
%>
<tr>
<td><%=no%></td>
<td><%=rst.getString("
book_name")%></td>
<td> <%=rst.getString("author")
%> </td>
</tr>
<%
no++;
}
rst.close();
stmt.close();
con.close();
%>
</table>
</center>
</body>
</html>
<%}else{%>
<html>
<head>
<title>Book Entry FormDocument</title>
<script language="javascript">
function validate(objForm){
if(objForm.bookname.value.length==0){
alert("Please enter Book Name!");
objForm.bookname.focus();
return false;
}
if(objForm.author.value.length==0){
alert("Please enter Author name!");
objForm.author.focus();
return false;
}
return true;
}
</script>
</head>
<body>
<center>
<form action="BookEntryForm.jsp" method="post"
name="entry" onSubmit="return
validate(this)">
<input type="hidden" value="list" name="action">
<table border="1" cellpadding="0" cellspacing="0">
<tr>
<td>
<table>
<tr>
<td colspan="2" align="center">
<h2>Book Entry Form</h2></td>
</tr>
<tr>
<td colspan="2"> </td>
</tr>
<tr>
<td>Book Name:</td>
<td><input name="bookname" type=
"text" size="50"></td>
</tr>
<tr>
<td>Author:</td><td><input name=
"author" type="text" size="50"></td>
</tr>
<tr>
<td colspan="2" align="center">
<input type="submit" value="Submit"></td>
</tr>
</table>
</td>
</tr>
</table>
</form>
</center>
</body>
</html>
<%}%>
Explanation of the above code:
Declaring Variables: Java is a strongly typed language which means, that variables must be explicitly declared before use and must be declared with the correct data types. In the above example code we declare some variables for making connection. Theses variables are-
Connection con=null;
ResultSet rst=null;
Statement stmt=null;
The objects of type Connection, ResultSet and Statement are associated with the Java sql. "con" is a Connection type object variable that will hold Connection type object. "rst" is a ResultSet type object variable that will hold a result set returned by a database query. "stmt" is a object variable of Statement .Statement Class methods allow to execute any query.
ResultSet rst=null;
Statement stmt=null;
The objects of type Connection, ResultSet and Statement are associated with the Java sql. "con" is a Connection type object variable that will hold Connection type object. "rst" is a ResultSet type object variable that will hold a result set returned by a database query. "stmt" is a object variable of Statement .Statement Class methods allow to execute any query.
Connection to database: The first task of this programmer is to load database driver. This is achieved using the single line of code :-
String driver = "org.gjt.mm.mysql.Driver";
Class.forName(driver).newInstance();
Class.forName(driver).newInstance();
The next task is to make a connection. This is done using the single line of code :-
String url="jdbc:mysql://localhost/books?user=<userName>&password=<password>";
con=DriverManager.getConnection(url);
con=DriverManager.getConnection(url);
When url is passed into getConnection() method of DriverManager class it returns connection object.
Executing Query or Accessing data from database:
This is done using following code :-
stmt=con.createStatement(); //create a Statement object
rst=stmt.executeQuery("select * from books_details");
stmt=con.createStatement(); //create a Statement object
rst=stmt.executeQuery("select * from books_details");
stmt is the Statement type variable name and rst is the RecordSet type variable. A query is always executed on a Statement object.
A Statement object is created by calling createStatement() method on connection object con.
A Statement object is created by calling createStatement() method on connection object con.
The two most important methods of this Statement interface are executeQuery() and executeUpdate(). The executeQuery() method executes an SQL statement that returns a single ResultSet object. The executeUpdate() method executes an insert, update, and delete SQL statement. The method returns the number of records affected by the SQL statement execution.
After creating a Statement ,a method executeQuery() or executeUpdate() is called on Statement object stmt and a SQL query string is passed in method executeQuery() or executeUpdate().
This will return a ResultSet rst related to the query string.
This will return a ResultSet rst related to the query string.
Reading values from a ResultSet:
while(rst.next()){
%>
<tr><td><%=no%></td><td><%=rst.getString("book_name")%></td><td><%=rst.getString("author")%></td></tr>
<%
}
The
ResultSet represents a table-like database result set. A ResultSet object maintains a cursor pointing to its current row of data. Initially, the cursor is positioned before the first row. Therefore, to access the first row in the ResultSet, you use the next() method. This method moves the cursor to the next record and returns true if the next row is valid, and false if there are no more records in the ResultSet object.Other important methods are
getXXX() methods, where XXX is the data type returned by the method at the specified index, including String, long, and int. The indexing used is 1-based. For example, to obtain the second column of type String, you use the following code:resultSet.getString(2);
You can also use the
getXXX() methods that accept a column name instead of a column index. For instance, the following code retrieves the value of the column LastName of type String.resultSet.getString("book_name");
The above example shows how you can use the
next() method as well as the getString() method. Here you retrieve the 'book_name' and 'author' columns from a table called 'books_details'. You then iterate through the returned ResultSet and print all the book name and author name in the format " book name | author " to the web page.Summary:
This article presents JDBC and shows how you can manipulate data in a relational database from your JSP page. To do this, you need to use the java.sql package:
Driver Manager, Connection, Statement, and ResultSet. Keep in mind, however, that this is only an introduction. To create a Web application, you need JDBC to use more features such as prepared statements and connection pooling.
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