1

好的，所以我创建了我的第一个 jsp 页面，它基本上创建了 3 个下拉菜单，并使用从数据库中提取的信息填充它们。

但是，有人告诉我这是错误的代码，我应该使用 servlet 来处理数据库功能和错误处理，并让 jsp 严格执行显示。

原jsp代码如下：

<%@page import="java.sql.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
                <title>Code Selector</title>
        </head>
        <body> 
            <h1>Please select the applicable codes:</h1> 
            <select name='Code' onchange="showState(this.value)">  
            <option value="none">Select a code</option>  
            <%
                //Pulls the ids and decriptions from the codes table and stores them in the first drop down
                try
                {
                    Class.forName("driverName").newInstance();  
                    Connection con = DriverManager.getConnection("serverURL","username","password");  
                    Statement stmt = con.createStatement();  
                    ResultSet rs = stmt.executeQuery("select id, descr from codes");

                    while(rs.next())
                    {
                        %>
                            <option value="<%=rs.getString(1)%>"><%=rs.getString(1)%> <%=rs.getString(2)%></option>  
                        <%
                    }

                    //Closes the database connection
                    stmt.close();
                    con.close();
                }
                catch (ClassNotFoundException e)
                {
                    System.err.println("ClassNotFoundException: " + e.getMessage());
                } 
                catch (SQLException e)
                {
                    System.err.println("SQLException: " + e.getMessage());
                }
                catch (Exception e)
                {
                    System.err.println("Generic Exception: " + e.getMessage());
                }       
            %>
            </select>  
            <br>
            <br>
            <select name='Code2' onchange="showState(this.value)">  
            <option value="none">Select a code</option>  
            <%
                //Pulls the ids and decriptions from the codes table and stores them in the second drop down
                try
                {
                    Class.forName("driverName").newInstance();  
                    Connection con = DriverManager.getConnection("serverURL","username","password");  
                    Statement stmt = con.createStatement();  
                    ResultSet rs = stmt.executeQuery("select id, descr from codes");

                    while(rs.next())
                    {
                        %>
                            <option value="<%=rs.getString(1)%>"><%=rs.getString(1)%> <%=rs.getString(2)%></option>  
                        <%
                    }

                    //Closes the database connection
                    stmt.close();
                    con.close();
                }
                catch (ClassNotFoundException e)
                {
                    System.err.println("ClassNotFoundException: " + e.getMessage());
                } 
                catch (SQLException e)
                {
                    System.err.println("SQLException: " + e.getMessage());
                }
                catch (Exception e)
                {
                    System.err.println("Generic Exception: " + e.getMessage());
                }       
             %>
            </select>
            <br>
            <br>
            <select name='otherCode' onchange="showState(this.value)">  
            <option value="none">Select a other code</option>  
            <%

                //Pulls the ids and decriptions from the other codes table and stores them in the third drop down
                try
                {
                    Class.forName("driverName").newInstance();  
                    Connection con = DriverManager.getConnection("serverURL","username","password");  
                    Statement stmt = con.createStatement();
                    ResultSet rs2 = stmt.executeQuery("select id, descr from other_codes");

                    while(rs2.next())
                    {
                        %>
                            <option value="<%=rs2.getString(1)%>"><%=rs2.getString(1)%> <%=rs2.getString(2)%></option>  
                        <%
                    }

                    //Closes the database connection
                    stmt.close();
                    con.close();
                }
                catch (ClassNotFoundException e)
                {
                    System.err.println("ClassNotFoundException: " + e.getMessage());
                } 
                catch (SQLException e)
                {
                    System.err.println("SQLException: " + e.getMessage());
                }
                catch (Exception e)
                {
                    System.err.println("Generic Exception: " + e.getMessage());
                }       
            %>
      </select>
      <br> 
      <br>
      <form method = "post">
        <input type="submit" value="Submit">
        <%
            try
            {
                String Code = request.getParameter("Code");
                String Code2 = request.getParameter("Code2");
                String otherCode = request.getParameter("otherCode");

                Class.forName("driverName").newInstance();  
                Connection con = DriverManager.getConnection("serverURL","username","password");  
                Statement stmt = con.createStatement();
                //ResultSet rs3 = stmt.executeQuery();

                System.out.println("This is the first code: " + Code);
                System.out.println("This is the second code: " + Code2);
                System.out.println("This is the other code: " + otherCode);

                con.close();
                stmt.close();

            }
            catch (ClassNotFoundException e)
            {
                System.err.println("ClassNotFoundException: " + e.getMessage());
            } 
            catch (SQLException e)
            {
                System.err.println("SQLException: " + e.getMessage());
            }
            catch (Exception e)
            {
                System.err.println("Generic Exception: " + e.getMessage());
            } 
        %>
        <script>
            window.close();
        </script>
      </form>
      </body> 
</html>

到目前为止，这就是我在新的 jsp 和 servlet 页面中所拥有的：

代码选择器.jsp

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML>
    <HEAD>
        <TITLE>
            Codes
        </TITLE>
    </HEAD>
    <BODY BGCOLOR="#FDF5E6">
        <H2 ALIGN="CENTER">
            Please select the applicable codes:
        </H2>
        <FORM ACTION="http://localhost:8088/SomeProgram" METHOD="GET">
            <CENTER>
                <select name='code' onchange="showState(this.value)">  
                    <option value="none">Select a code</option>  
                </select>
                <BR>
                <BR>
                <select name='code2' onchange="showState(this.value)">  
                    <option value="none">Select a code</option>  
                </select>
                <BR>
                <BR>
                <select name='otherCode' onchange="showState(this.value)">  
                    <option value="none">Select an other code</option>  
                </select>
                <BR>
                <BR>
                <!-- Press this to submit form -->
                <INPUT TYPE="SUBMIT" VALUE="Submit"/>
            </CENTER>
        </FORM>
    </BODY>
</HTML>

PullCodes.java (servlet)：

package com.firstservlet.alfresco;

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

import java.sql.*;

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

    /**
     * @see HttpServlet#HttpServlet()
     */
    public PullCodes() 
    {
        super();
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {
        String code = request.getParameter("code");
        String code2 = request.getParameter("code2");
        String otherCode = request.getParameter("otherCode");

        try
        {
            Class.forName("driverName").newInstance();  
            Connection con = DriverManager.getConnection("url","username","password");  
            Statement stmt = con.createStatement();  
            ResultSet rs = stmt.executeQuery("select id, descr from ref_codes");
            ResultSet rs2 = stmt.executeQuery("select id, descr from ref_other_codes");

            try
            {
                while(rs.next())
                {
                    //Is this correct?
                                    code+=("<option value=\"" + rs.getString(1) + "\">" + rs.getString(1) + " " + rs.getString(2) + "</option>");
                }

                //Closes the database connection
                stmt.close();
                con.close();
            }
            catch (Exception e)
            {
                System.err.println("Insertion Exception: " + e.getMessage());
            }       
        }
        catch (ClassNotFoundException e)
        {
            System.err.println("ClassNotFoundException: " + e.getMessage());
        } 
        catch (SQLException e)
        {
            System.err.println("SQLException: " + e.getMessage());
        }
            catch (Exception e)
        {
            System.err.println("Generic Exception: " + e.getMessage());
        }   
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {
        // TODO Auto-generated method stub
    }

}

所以现在，在这一点上，我不确定如何从我的 html 页面访问该下拉列表元素。谷歌搜索，我没有看到任何似乎表明这已经完成的东西。此外，从我读到的内容看来，大多数时候 servlet 只是在处理来自 html/jsp 页面的信息。我现在正在做的是code+=("<option value=\"" + rs.getString(1) + "\">" + rs.getString(1) + " " + rs.getString(2) + "</option>");。那是对的吗？如果是这样，我如何将它与 html/jsp 页面链接？或者甚至无法在加载时访问该 html 页面并使用 servlet 填充它？

4

2 回答 2

1

经典模式是：

Browser -- request --> Servlet -- forward --> JSP

Servlet 用来向 JSP 传递信息的机制是通过将值放入实际请求中。

public void doGet(HttpServletRequest req, HttpServletResponse res)
    throws ServletException, IOException {
    String id = req.getParameter("id");
    String name = getNameFromDBForId(id);
    req.setAttribute("name", name);
    RequestDispatcher rd = getServletContext().getRequestDispatcher("/page.jsp");
    rd.forward(request, response);
}

然后你可以使用 JSP EL（表达语言）：

<html>
  <body>
    <h1>Hello ${name}</h1>
  </body>
</html>

EL 表达式在多个位置${name}查找name键，其中一个是请求（您可以查找其他位置），并替换 JSP 中的值。

这适用于简单的标量、java bean、集合。

但这是如何将数据从 Servlet 获取到 JSP 的基本机制。查找 JSTL 标记，例如迭代和条件逻辑。

于 2012-09-28T16:10:03.770 回答
0

你应该使用 JSTL 标签。scriptlet 是不可信的，并且很难维护。 检查此链接以获取 JSTL SQL 相关标签

于 2012-09-28T15:40:01.380 回答