从servlet传递ArrayList到JSP页面

Question

从servlet传递ArrayList到JSP页面

11

我想将包含对象的ArrayList从servlet传递到JSP。但是

servlet文件：

request.setAttribute("servletName", categoryList); //categorylist is an arraylist      contains object of class category  
getServletConfig().getServletContext().getRequestDispatcher("/GetCategory.jsp").forward(request,response);

JSP文件：

//category class    
<% Category category = new Category();
//creating arraylist object of type category class
ArrayList<Category> list = ArrayList<Category>();
//storing passed value from jsp
list = request.getAttribute("servletName");

for(int i = 0; i < list.size(); i++) {

category = list.get(i);

out.println( category.getId());

out.println(category.getName());

out.println(category.getMainCategoryId() );
}
%>

- Pravin

1

为什么不使用JSP-EL+JSTL来处理对象呢？其次，您是如何从Servlet到达JSP的？是使用重定向还是转发？ - Dave G

@DebojitSaikia 结果没有显示任何内容。 - Pravin

@DaveG 我是一个初学者，不了解 JSP-EL+JSTL … 我正在使用以下代码在 servlet 中传递值 … getServletConfig().getServletContext().getRequestDispatcher("/GetCategory.jsp").forward(request,response); - Pravin

@user2952188 尝试使用 request.getRequestDispatcher('/jspFile.jsp').forward(request,response) 获取调度程序，并确保在转发请求后，servlet 不会执行任何操作。换句话说，在重定向或转发后，您不允许使用请求/响应。 - user2511414

@user2952188，没错，它可以工作，但更好（更简单）的方法是使用请求。 setAttribute() 方法接受 Object，这意味着您可以设置任何内容。 - user2511414

显示剩余2条评论

6个回答

6

request.getAttribute("servletName") 方法将返回一个 Object，您需要将其转换为 ArrayList。

ArrayList<Category> list =new ArrayList<Category>();
//storing passed value from jsp
list = (ArrayList<Category>)request.getAttribute("servletName");

- Prabhakaran Ramaswamy

1

你忘记在构造函数 new ArrayList<Category>() 前加上 new 关键字了 :) - user2511414

1

<html>
    <%

        ArrayList<Actor> list = new ArrayList<Actor>();
        list = (ArrayList<Actor>) request.getAttribute("actors");
    %>
<head>
    <link rel="stylesheet" type="text/css" href="style.css">
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Actor</title>
</head>

<body>

    <h2>This is Actor Class</h2>
    <table>
        <thead>
            <tr>
                <th>Id</th>
                <th>First Name</th>
                <th>Last Name</th>
            </tr>
        </thead>
        <tbody>
            <% for(int i = 0; i < list.size(); i++) {
                Actor actor = new Actor();
                actor = list.get(i);
                //out.println(actor.getId());
                //out.println(actor.getFirstname());
                //out.println(actor.getLastname());
            %>


            <tr>
                <td><%=actor.getId()%></td>
                <td><%=actor.getFirstname()%></td>
                <td><%=actor.getLastname()%></td>
               </tr>
            <%
            };
            %>
        </tbody>
    </table>

</body>

- Ralph Weber

1

public class myActorServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
    private String name;
    private String user;
    private String pass;
    private String given_table;
    private String tid;
    private String firstname;
    private String lastname;
    private String action;

    @Override
    public void doPost(HttpServletRequest request,
            HttpServletResponse response)
            throws IOException, ServletException {

        response.setContentType("text/html");

        // connecting to database
        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;

        PrintWriter out = response.getWriter();
        name = request.getParameter("screenName");
        user = request.getParameter("username");
        pass = request.getParameter("password");
        tid = request.getParameter("tid");
        firstname = request.getParameter("firstname");
        lastname = request.getParameter("lastname");
        action = request.getParameter("action");
        given_table = request.getParameter("tableName");

        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet JDBC</title>");
        out.println("<link rel=\"stylesheet\" type=\"text/css\" href=\"style.css\">");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Hello, " + name + " </h1>");
        out.println("<h1>Servlet JDBC</h1>");

        /////////////////////////
        // init connection object
        String sqlSelect = "SELECT * FROM `" + given_table + "`";
        String sqlInsert = "INSERT INTO `" + given_table + "`(`firstName`, `lastName`) VALUES ('" + firstname + "', '" + lastname + "')";
        String sqlUpdate = "UPDATE `" + given_table + "` SET `firstName`='" + firstname + "',`lastName`='" + lastname + "' WHERE `id`=" + tid + "";
        String sqlDelete = "DELETE FROM `" + given_table + "` WHERE `id` = '" + tid + "'";

        //////////////////////////////////////////////////////////
        out.println(
                "<p>Reading Table Data...Pass to JSP File...Okay<p>");

        ArrayList<Actor> list = new ArrayList<Actor>();
        // connecting to database
        try {
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/javabase", user, pass);
            stmt = con.createStatement();
            rs = stmt.executeQuery(sqlSelect);
            // displaying records

            while (rs.next()) {
                Actor actor = new Actor();
                actor.setId(rs.getInt("id"));
                actor.setLastname(rs.getString("lastname"));
                actor.setFirstname(rs.getString("firstname"));
                list.add(actor);
            }
            request.setAttribute("actors", list);
            RequestDispatcher view = request.getRequestDispatcher("myActors_1.jsp");
            view.forward(request, response);

        } catch (SQLException e) {
            throw new ServletException("Servlet Could not display records.", e);
        } catch (ClassNotFoundException e) {
            throw new ServletException("JDBC Driver not found.", e);
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                    rs = null;
                }
                if (stmt != null) {
                    stmt.close();
                    stmt = null;
                }
                if (con != null) {
                    con.close();
                    con = null;
                }
            } catch (SQLException e) {
            }
        }
        out.println("</body></html>");

        out.close();
    }

}

- Ralph Weber

0

可能出现的错误包括：
1.您将数组列表从servlet设置到会话中，而不是请求中。
2.您设置的数组为空。
3.您重定向页面而不是转发它。

此外，您不应该在JSP中初始化list和category。请尝试以下操作。

for(Category cx: ((ArrayList<Category>)request.getAttribute("servletName"))) {

out.println( cx.getId());

out.println(cx.getName());

out.println(cx.getMainCategoryId() );
}

- user2511414

-2

这里列出了在请求中设置的属性名称：request.setAttribute("List",list); 和 ArrayList list=new ArrayList();

<%

ArrayList<Category> a=(ArrayList<Category>)request.getAttribute("List");

out.print(a);

for(int i=0;i<a.size();i++)

{
    out.println(a.get(i));

}


%>

- Pradeep Angre

JSP如何知道Category类的存在？ - user3217883

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- Cadavere · Accepted Answer

在Servlet代码中，使用指令request.setAttribute("servletName", categoryList)将列表保存在请求对象中，并使用名称"servletName"来引用它。
顺便说一下，使用名称"servletName"来表示列表可能会令人困惑，最好称其为"list"或类似的名称：request.setAttribute("list", categoryList)
无论如何，假设您不更改Servlet代码并使用名称"servletName"存储列表。当到达JSP时，需要从请求中检索列表，只需使用request.getAttribute(...)方法即可。

<%  
// retrieve your list from the request, with casting 
ArrayList<Category> list = (ArrayList<Category>) request.getAttribute("servletName");

// print the information about every category of the list
for(Category category : list) {
    out.println(category.getId());
    out.println(category.getName());
    out.println(category.getMainCategoryId());
}
%>