There are two distinct methods for connecting to the database using JSP. The JSP will be compiled into a servlet, and that happens automatically each time you change the code. The first method makes database connections in the .jsp page itself, while the second one sets up the database connection in a separate class (called a bean in Java server programming).
Here is an example for connecting to the Oracle database through JSP. This approach mixes the presentation and logic. Using a bean allows separating those.
This is very similar to accessing the database through a java application, except that it is not run by the user who writes the code. As a result, the classpath settings are different. As long as you use the directory structure discussed below, you should not have problems with the class path.
This method is not recommended as it may expose your username and password if you are using a shared environment such as the department lab. This is because the public_html directory cannot be read protected and still serve its purpose. Using a bean eliminates this problem and is much more commonly used in real-world/business situations.
<html>
<head>
</head>
<body>
<%@ page import="java.sql.*" %>
<%@ page import="java.io.*" %>
<%
//
Class.forName("oracle.jdbc.driver.OracleDriver");
// Initialize connection to database
// Remember to change username and password
Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@db1.chpc.ndsu.nodak.edu:1521:cs", "username", "password");
// Create a statement and a query, execute the query
Statement stmt = conn.createStatement();
String query = ""; //Remember to change this to match your database
ResultSet rset = stmt.executeQuery(query);
// Iterate through all result rows
while(rset.next())
{
// Print the first item of the result
out.println(rset.getString(1));
// Print a line break
out.println("<br/>");
}
// Clean up
stmt.close();
rset.close();
conn.close();
%>
</body>
</html>
If you want to split presentation and database access to make a 3-tier application (presentation, logic, database), you will need two pieces:
The logic layer (database queries and other logic) will be implemented in a class, the presentation layer (your JSP/HTML) will call functions of the class, and the class will do the work of getting data from the database.
You will need a class for your logic layer. This class needs to be part of a package otherwise the server won't be able to access it.
Here is an example class:
package beans;
import java.io.*;
import java.sql.*;
import java.util.*;
public class DBCon
{
public DBCon()
{
// empty constructor
}
public ArrayList getRecords()
throws SQLException, ClassNotFoundException
{
ArrayList records = new ArrayList();
// Load Oracle driver
Class.forName("oracle.jdbc.driver.OracleDriver");
// Initialize connection to database
// Remember to change username and password
Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@db1.chpc.ndsu.nodak.edu:1521:cs", "username", "password");
// Create a statement and a query, execute the query
Statement stmt = conn.createStatement();
String query = ""; //Remember to change this to match your database
ResultSet rset = stmt.executeQuery(query);
// Iterate through all result rows
while(rset.next())
{
records.add(rset.getString(1));
}
// Clean up
stmt.close();
rset.close();
conn.close();
return records;
}
}
This class is part of the package 'beans'. There is a single function that returns the first item of each query result. You will want to add functions or change this function to match your database and project. These functions can be called by the JSP page.
Once compiled, this class needs to be placed in the folder: /home/username/public_html/WEB-INF/classes/<packagename>/ where '<packagename>' is the name of the package your class belongs to. In this case the package name is 'beans'.
The JSP page will be placed in the public_html directory, and can be reached through the URL http://students.cs.ndsu.nodak.edu/~uuid/mypage.jsp
To use the database functions defined in your bean, you need to use a special JSP directive.
You can import packages using the syntax:
<%@page import="java.util.*"%>
This imports java.util.*
To import your bean, use the syntax:
<jsp:useBean id="dbcon" scope="request" class="beans.DBCon" />
This defines an object called 'dbcon'. It has a scope of 'request', meaning that the dbcon object is the same throughout the request (options for scope include 'page', 'request', 'session'). The attribute 'class' tells the server which class to use for this object.
This is similar to the java:
DBCon dbcon = new DBCon();
in that it makes a new object for code the use. The difference is that jsp:useBean is used for JSP pages to load Beans.
Here is a small JSP page that loads the DBCon bean and calls the function getRecords(). Note that we do not specify ANY database connection information here, that's taken care of in the DBCon bean.
<html>
<head></head>
<body>
<%@page import="java.util.*"%>
<jsp:useBean id="dbcon" scope="request" class="beans.DBCon" />
<%
// Get the first item of each record by calling a function of the DBCon class
ArrayList records = dbcon.getRecords();
// Go through each record and print
for(int i = 0; i < records.size(); i++)
{
// Print out each item in the 'records' array
out.println(" item: " + (String)records.get(i));
out.println("<br/>");
}
%>
</body>
</html>