How to post the result of a sql query into a servlet?
I keep getting stuck on this.
Here is my servlet:
package HWpackage;
import java.io.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.*;
import javax.servlet.http.*;
public class DemoData extends HttpServlet {
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
try {
out.println("<html>");
out.println("<head>");
out.println("<title>Demo of Data Persistence</title>");
out.println("</head>");
out.println("<body>");
try {
String driver = "oracle.jdbc.driver.OracleDriver";
String url = "jdbc:oracle:thin:@coit-ora01.u开发者_运维技巧ncc.edu:1521:class";
String username = "johnR";
String password = "lAylko0K";
// Load database driver if it's not already loaded.
Class.forName(driver);
// Establish network connection to database.
Connection connection =
DriverManager.getConnection(url, username, password);
// Create a statement for executing queries.
Statement statement = connection.createStatement();
String query =
"SELECT sum(cost) FROM stocks where username = 'Bora'";
// Send query to database and store results.
ResultSet resultSet = statement.executeQuery(query);
while(resultSet.next()) {
out.println("Your total cost is" );
}
connection.close();
} catch(ClassNotFoundException cnfe) {
System.err.println("Error loading driver: " + cnfe);
// Useful when you debug your program on the coit server
// where System.out.println("") becomes futile
out.println("<tr> Error loading driver: " + cnfe);
out.println("</tr>");
} catch(SQLException sqle) {
System.err.println("Error with connection: " + sqle);
// Again, for debug purpose
out.println("<tr> Error with connection: " + sqle);
out.println("</tr>");
}
out.println("</table>");
out.println("</body>");
out.println("</html>");
} finally {
out.close();
}
}
// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
* Handles the HTTP <code>GET</code> method.
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
/**
* Handles the HTTP <code>POST</code> method.
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
/**
* Returns a short description of the servlet.
* @return a String containing servlet description
*/
public String getServletInfo() {
return "Short description";
}// </editor-fold>
}
I'd like to know the correct way to post the result of this query in the servlet:
String query =
"SELECT sum(cost) FROM stocks where username = 'Bora'";
after the is
out.println("Your total cost is" );
If someone could provide me that information you will seriously make my night. Thanks everyone.
One of the ways is to do this:-
SELECT sum(cost) AS COST FROM stocks where username = 'Bora'In this code block modify to:
while(resultSet.next()) {
Double cost = resultSet.getDouble("COST"); out.println("Your total cost is" + cost );}
Side notes:
- Do not hard code sql parameters this way. You are prone to SQL injection attacks. Use parameter markers ie.
`SELECT sum(cost) AS COST FROM stocks where username = ?and JDBC PreparedStatement to execute it. - Create a separate DAO class for handing all database work. This will promote decoupling in your code.
out.println("Your total cost is "+resultSet.getString("sum(cost)"));
加载中,请稍侯......
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