Collegando alla database in Servlets

Un servlet pu� generare uno o pi� Connectionobject nel relativo metodo del init () e riutilizzarlo nel relativo servizio (), nel doGet () e nei metodi del doPost (). Per dimostrare, l'esempio 9-4 mostra il servlet di occhiata del telefono riscritto per generare in anticipo i relativi oggetti del collegamento. Inoltre usa HtmlSQLResult per visualizzare i risultati. Si noti che questo servlet usa il driver di Sybase JDBC.

Collegamento della database di Servlets usando la databasedi Mysql

// File: ShowBedrock.java

/* A servlet to display the contents of the MySQL Bedrock database */

import java.io.*;
import java.net.*;
import java.sql.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class ShowBedrock extends HttpServlet
{
public String getServletInfo()
{
return "Servlet connects to MySQL database and displays result of a SELECT";
}

// Use http GET

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
String loginUser = "Dude1";
String loginPasswd = "SuperSecret";
String loginUrl = "jdbc:mysql://localhost:3306/bedrock";

response.setContentType("text/html"); // Response mime type

// Output stream to STDOUT
PrintWriter out = response.getWriter();

out.println("<html><head><title>Bedrock</title></head>");
out.println("<body><h1>Bedrock</h11>");

// Load the mm.MySQL driver
try
{
Class.forName("org.gjt.mm.mysql.Driver");
Connection dbcon = DriverManager.getConnection(loginUrl, loginUser, loginPasswd);
// Declare our statement
Statement statement = dbcon.createStatement();

String query = "select name, dept, ";
query += " jobtitle ";
query += "from employee ";

// Perform the query
ResultSet rs = statement.executeQuery(query);

out.println("<table border>");

// Iterate through each row of rs
while (rs.next())
{
String m_name = rs.getString("name");
String m_dept = rs.getString("dept");
String m_jobtitle = rs.getString("jobtitle");
out.println("<tr>" +
"<td>" + m_name + "</td>" +
"<td>" + m_dept + "</td>" +
"<td>" + m_jobtitle + "</td>" +
"</tr>");
}

out.println("</table>");

rs.close();
statement.close();
dbcon.close();
}
catch (SQLException ex) {
while (ex != null) {
System.out.println ("SQL Exception: " + ex.getMessage ());
ex = ex.getNextException ();
} // end while
} // end catch SQLException

catch(java.lang.Exception ex)
{
out.println("<html>" +
"<head><title>" +
"Bedrock: Error" +
"</title></head>\n<body>" +
"<p>SQL error in doGet: " +
ex.getMessage() + "</p></body></html>");
return;
}
out.close();
}
}