Passing ArrayList from servlet to JSP

2020-01-31 07:46发布

站内问答 / Java
1811 6 6

I am trying to pass ArrayList which contains object from servlet to JSP. But

Servlet file:

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

JSP file:

//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() );
}
%>

6条回答
够拽才男人
2楼-- · 2020-01-31 08:03

the possible errors would be...
1.you set the array list from the servelt in the session, not the in the request.
2.the array you set is null.
3.you redirect the page instead of forward it.

also you should not initialize the list and the category in jsp. try this. 

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

out.println( cx.getId());

out.println(cx.getName());

out.println(cx.getMainCategoryId() );
}
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干净又极端
3楼-- · 2020-01-31 08:04

here list attribute name set in request request.setAttribute("List",list); and 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));

}


%>
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手持菜刀，她持情操
4楼-- · 2020-01-31 08:05

In the servlet code, with the instruction request.setAttribute("servletName", categoryList), you save your list in the request object, and use the name "servletName" for refering it.
By the way, using then name "servletName" for a list is quite confusing, maybe it's better call it "list" or something similar: request.setAttribute("list", categoryList)
Anyway, suppose you don't change your serlvet code, and store the list using the name "servletName". When you arrive to your JSP, it's necessary to retrieve the list from the request, and for that you just need the request.getAttribute(...) method.

<%  
// 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());
}
%>
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成全新的幸福
5楼-- · 2020-01-31 08:06 
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();
    }

}
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贪生不怕死
6楼-- · 2020-01-31 08:08

request.getAttribute("servletName") method will return Object that you need to cast to ArrayList

ArrayList<Category> list =new ArrayList<Category>();
//storing passed value from jsp
list = (ArrayList<Category>)request.getAttribute("servletName");
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做自己的国王
7楼-- · 2020-01-31 08:13 
<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>

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