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Database Access. What is a database system?. Data (database). Programs that handle the data (database server). Programming language (SQL). Typical Configuration. How it’s used by a webserver?. CGI program realizes dbase needs to be accessed.

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Presentation Transcript
what is a database system
What is a database system?
  • Data (database).
  • Programs that handle the data (database server).
  • Programming language (SQL).
how it s used by a webserver
How it’s used by a webserver?
  • CGI program realizes dbase needs to be accessed.
  • It asks dbase server to get data (using SQL commands).
  • Dbase server returns data.
  • CGI program formats data in HTML and writes HTML to Browser.
several ways a cgi program can interfere with dbase system
Several ways a CGI program can interfere with Dbase system
  • Using a custom method used by that particular dbase server.
  • Using a standard access method like ODBC/JDBC.
  • Rolling the CGI program and dbase client into a single unit.
  • Placing the entire webserver inside the dbase server/client. (e.g., webserver is an Oracle OCI program).
jdbc access from a servlet
JDBC access from a servlet
  • What is JDBC?
    • JDBC = Java DataBase Connectivity.
    • JDBC is really a Java class library (java.sql) that provides a standard way to access databases.
    • The idea is that, you can write code using JDBC, and not worry about the specifics of the database server.
    • Today, most database servers come with a JDBC component.
sample servlet that access a database
Sample servlet that access a database

else {

System.out.println ("Connection successful. Continuing ...");

}

// Make a statement.

Statement s = con.createStatement();

if (s == null) {

System.out.println ("Statement creation unsuccessful");

System.exit(0);

}

else {

System.out.println ("Statement creation successful ... continuing");

}

// Execute the SQL statement.

if ( s.execute (sql) ) {

ResultSet r = s.getResultSet();

ResultSetMetaData meta = r.getMetaData();

int cols = meta.getColumnCount();

int rownum = 0;

// Iterate over the rows - get one row at a time.

while( r.next() ) {

rownum++;

System.out.println("Row: " + rownum);

for(int i=0; i<COLS; body (?");

out.println ("");

out.close();

// Screen I/O

System.out.println ("Inside servlet ... servlet complete");

}

public void doPost (HttpServletRequest req, HttpServletResponse resp)

throws ServletException, IOException

{

doGet (req, resp);

}

import javax.servlet.*;

import javax.servlet.http.*;

import java.sql.*;

import java.net.*;

import java.io.*;

public class TestJDBCServlet extends HttpServlet {

public void doGet (HttpServletRequest req, HttpServletResponse resp)

throws ServletException, IOException

{

// Set the content type of the response.

resp.setContentType ("text/html");

// Create a PrintWriter to write the response.

java.io.PrintWriter out = new PrintWriter (resp.getOutputStream());

// The first part of the response.

out.println ("");

out.println ("");

out.println ("");

// The SQL query.

String sql = "select * from emp";

System.out.println("Executing: " + sql);

// Create a driver instance.

try {

Class.forName("com.imaginary.sql.msql.MsqlDriver").newInstance();

// Make a connection.

String url = "jdbc:msql://localhost:8114/test";

Connection con = DriverManager.getConnection(url, "simha", "");

if (con == null) {

System.out.println ("Connection unsuccessful");

System.exit(0);

}

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