我一直卡在这个问题上。
这是我的 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.uncc.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>
}
我想知道在 servlet 中发布此查询结果的正确方法:
String query =
"SELECT sum(cost) FROM stocks where username = 'Bora'";
之后是
out.println("Your total cost is" );
如果有人可以向我提供这些信息，你将让我度过一个愉快的夜晚。谢谢大家。
最佳答案
其中一种方法是这样做:-
SELECT sum(cost) AS COST FROM stocks where username = 'Bora'在此代码块中修改为:
while(resultSet.next()) {
Double cost = resultSet.getDouble("COST"); out.println("Your total cost is" + cost );}
旁注:
- 不要以这种方式对 sql 参数进行硬编码。你很容易SQL injection攻击。使用参数标记即。
`SELECT sum(cost) AS COST FROM stocks where username = ?and JDBC PreparedStatement执行它。 - 创建一个单独的 DAO处理所有数据库工作的类。这将促进代码中的解耦。
关于java - 如何将 sql 查询的结果发布到 servlet 中？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5615720/