Question

在我的Java EE项目中，我有以下Servlet：

import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;

import javax.naming.InitialContext;
import javax.servlet.RequestDispatcher;
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 javax.sql.DataSource;

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

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

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

        System.out.println("Inside doGet()!");

        ArrayList<BeanTitle> bt=new ArrayList<BeanTitle>();

        java.io.PrintWriter out = response.getWriter();
        response.setContentType("text/html"); 

        Connection conn=null;


        try {
            /* get the DataSource from using the JNDI name */
            Class.forName("com.mysql.jdbc.Driver");
            InitialContext ctx = new InitialContext();
            DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/Test");

            //Create connection and then continue as usual other JDBC calls 
            conn=ds.getConnection();
            System.out.println("\nConnection Successful in TitlePopulatorServlet !");
            Statement s= conn.createStatement();
            ResultSet rs=s.executeQuery("SELECT * FROM story");

            while (rs.next() ) 
            {
                BeanTitle b = new BeanTitle();
                b.setBtitle(rs.getString(1));
                bt.add(b);
            }

        } catch (Exception e){
            out.println("Failed!"+ e);
        }


            request.setAttribute("bt", bt);                                                         
            request.getRequestDispatcher("/StoryTitlePage.jsp").forward(request,response);


    }

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



    }
}

BeanTitle如下：

public class BeanTitle 
{
    private String btitle;

    public String getBtitle() {
        return btitle;
    }

    public void setBtitle(String btitle) {
        this.btitle = btitle;
    }
}

JSP页面（＆＃34; StoryTitlePage.jsp＆＃34;）如下：

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">


<html>
<head>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<jsp:useBean id="storylist" class="serv.TitlePopulatorServlet" scope="request" />

<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

<title>Story Title Page</title>
</head>
<body>

<form action="/ReportData/DisplayReport" method="post" >

        Please select an element: 

        <select id="selectedRecord" name="selectedRecord">

            <c:forEach var="item" items=${storylist.bt} >
                <option>${item.tarr}</option>
            </c:forEach>
        </select>

        <input type="submit" value="Submit"> 

    </form>

</body>
</html>

但是当我在服务器上启动TitlePopulatorServlet时它不起作用。在迭代/ EL中我哪里出错？

Answer 1

servlet将列表存储在请求中，名为＆＃34; bt＆＃34;。所以它已经存在于请求中。没有必要这样做

<jsp:useBean id="storylist" class="serv.TitlePopulatorServlet" scope="request" />

这只会创建一个servlet的新实例，这没有任何意义。和bt是一个请求属性。它不是servlet的属性。因此，使用${storylist.bt}也没有任何意义。

你想迭代bt的元素，所以你需要的只是

<c:forEach var="item" items="${bt}">

最后，bt的每个项目都是BeanTitle类型。而你正在做

${item.tarr}

这相当于调用

beanTitle.getTarr()

BeanTitle中没有tarr属性。唯一的属性是btitle（因为该类的唯一getter名为getBTitle()）。

所以你必须使用的是

${item.btitle}

你的命名很糟糕，这只会让你更加困惑。为什么不用真实的单词来命名你的类和属性？例如

public class Book {
    private String title;

    public String getTitle() 

    ...
}

从Bean类型的Array List中填充JSP中的下拉列表

1 个答案: