java - SQL查询返回 "oracle.jdbc.driver.OracleResultSetImpl@48f675"而不是我预期的数据

Question

我已成功连接到数据库，但是当尝试使用 Java servlet 转发请求将 SQL 查询结果返回到我的 index.jsp 页面时，收到“oracle.jdbc.driver.OracleResultSetImpl@48f675”的输出，而不是预期的数据结果。 (注意:我在 Eclipse 的控制台 View 中收到来自 SQL 查询的预期结果；但是，数据没有像我预期的那样显示在我的 jsp 页面上。而是显示了 ResultSetImp 消息。任何人都可以分享关于为什么我得到这个 ResultSetImp 而不是我的预期数据的见解，我们将不胜感激。还有人愿意解释 ResultSetImp 的意思吗...我的搜索没有找到任何有用的东西，或者至少是我理解的。代码如下:

package com.database;
import java.sql.*;


public class DBConnection {

public static void main(String[] args) 
throws ClassNotFoundException, SQLException{

}

    public static ResultSet queryExecute() throws ClassNotFoundException, SQLException
    {

    Class.forName("oracle.jdbc.OracleDriver");  
    Connection conn = DriverManager.getConnection("**Connection string here**");

    if (conn == null)
    {
        System.out.println("Database connection not successfull");
    }
    else 
    {
        System.out.println("Database connection success!");
        //System.out.println(conn);
    }


        Statement stmt = conn.createStatement();
        //ResultSet rs = stmt.executeQuery("SELECT COUNT(*) FROM Request natural join RequestTerm");
        ResultSet rs = stmt.executeQuery("select * from (select QIPNUMBER,model,SERIALNUMBER,YEAROFMFG,DATERECEIVED,TERM,DEALERNAME from Request natural join RequestTerm)WHERE ROWNUM <= 20");
        ResultSetMetaData rsmd = rs.getMetaData();
        int columnsNumber = rsmd.getColumnCount(); 
        //List<String> displayRecords = new ArrayList<String>(); try store result set into an array object


        while (rs.next()) {
            // Iterate through the data in the result set and display it. 

           //int count = rs.getInt(1);
          while (rs.next()) {
          //Print one row          
          for(int i = 1 ; i <= columnsNumber; i++){

                System.out.print(rs.getString(i) + " " + "    "); //Print one element of a row -- print vs println

          }

            System.out.println(); //Move to the next line to print the next row.  
            //System.out.println("Number of row:"+count);
              }
        }

    rs.close();
    stmt.close();
    conn.close();
    return rs;

    }

} 

我的servlet代码:

package com.srccodes.example;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.SQLException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

导入com.database.DBConnection;

   /**
    * Servlet implementation class HelloWorld
    */
@WebServlet("/HelloWorld")
public class HelloWorld extends HttpServlet {
   public static final long serialVersionUID = 1L;

/**
 * @see HttpServlet#HttpServlet()
 */
  public HelloWorld() {
    super();
    // TODO Auto-generated constructor stub
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

  response.setContentType("text/html");
  PrintWriter printWriter  = response.getWriter();
  printWriter.println("<h1>Hello from the doGet function!</h1>");
}


/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    try {
        //ResultSet display = DBConnection.queryExecute();
        request.setAttribute("display", DBConnection.queryExecute());
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }
    request.getRequestDispatcher("/index.jsp").forward(request, response);

    /*String nextJSP = "/result.jsp";
    RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(nextJSP);
    dispatcher.forward(request,response);*/
}

}

最后，我用来在 index.jsp 中调用 servlet 的语句:

<%= request.getAttribute("display")%>我知道这种说法是潦草的，会让人皱眉；但是，我试图先将数据填充到我的 jsp 中，然后从那里移动。

Answer 1

当您返回 ResultSet 对象时，您将获得该对象的引用。您不会如您所愿地获得其中的值。

你必须做这样的事情(如果你真的想使用 scriplet):

<%
ResultSet rs = (ResultSet)request.getAttribute("display");

ResultSetMetaData rsmd = rs.getMetaData();
        int columnsNumber = rsmd.getColumnCount(); 

        while (rs.next()) {

          for(int i = 1 ; i <= columnsNumber; i++){
                out.print(rs.getString(i) + " " + "    " + "<br/>");
          }

            out.print("<br/>"); //Move to the next line to print the next row.  
            }
        }

    rs.close();
%>

更合适的方法是使用 bean:

class MyBean {
 int QIPNUMBER;
 String model;
 .....
 //getters and setters


}

现在在您的类中创建 MyBean 列表并填充对象，一行 = 一个对象。

List<MyBean> lst = new ArrayList<MyBean>();
MyBean myBean;
while (rs.next()) {
          myBean = new MyBean();
          myBean.setModel(rs.getString("model"));
          ....
          lst.add(myBean);
}
.....

return lst;

在此之后添加要在 Servlet 中请求的列表，而不是结果集。

request.setAttribute("display", DBConnection.queryExecute());
// queryExecute now returns List<MyBean>

现在在您的 JSP 中，如果您想使用 scriplet，那么:

<%
   List<MyBean> lst = (ArrayList<MyBean>)request.getAttribute("display");
   for(MyBean mb : lst){
       out.print(mb.getModel() + "<br/>");
       .....
   }
%>