Java 如何将sql查询的结果发布到servlet中？_Java_Sql_Servlets

Java 如何将sql查询的结果发布到servlet中？

java sql servlets

Java 如何将sql查询的结果发布到servlet中？,java,sql,servlets,Java,Sql,Servlets,我一直被困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.servle

我一直被困在这个问题上

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" );

如果有人能给我提供这些信息，你会让我很高兴的。谢谢大家。

方法之一是：-

out.println("Your total cost is "+resultSet.getString("sum(cost)"));

选择sum（cost）作为用户名为'Bora'的库存成本

在此代码块中，修改为：

while（resultSet.next（））{

}

旁注：

不要以这种方式硬编码sql参数。你很容易受到攻击。使用参数标记，即从username=？和JDBC中选择sum（cost）作为成本

创建一个单独的类来处理所有数据库工作。这将促进代码中的解耦

我不明白问题是什么，你能详细说明一下吗？“将SQL查询的结果发布到servlet”是什么意思？这里还有一个问题……我设置了一个DAO，但我一直在试图弄清楚如何将结果集从DAO拉到另一个servlet中。我如何调用结果集并将其设置为字符串？您不调用结果集，而是调用DAO方法。DAO方法将确定如何执行查询，并以字符串、双精度或任何适用的形式返回数据。

            Double cost = resultSet.getDouble("COST");   
            out.println("Your total cost is" + cost );