Java 将 ArrayList 从 servlet 传递到 JSP
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Passing ArrayList from servlet to JSP
提问by Pravin
I am trying to pass ArrayList which contains object from servlet to JSP. But
我试图将包含对象的 ArrayList 从 servlet 传递到 JSP。但
Servlet file:
服务文件：
request.setAttribute("servletName", categoryList); //categorylist is an arraylist contains object of class category
getServletConfig().getServletContext().getRequestDispatcher("/GetCategory.jsp").forward(request,response);
JSP file:
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() );
}
%>
采纳答案by Cadavere
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.
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。
顺便说一句，使用然后名称“servletName”作为一个列表是相当混乱的，也许最好将它称为“列表”或类似的东西： request.setAttribute("list", categoryList)
无论如何，假设您不更改您的 serlvet 代码，并使用名称“servletName”存储列表”。当您到达 JSP 时，有必要从请求中检索列表，为此您只需要该request.getAttribute(...)方法。
<%
// 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());
}
%>
回答by Prabhakaran Ramaswamy
request.getAttribute("servletName")method will return Objectthat you need to cast to ArrayList
request.getAttribute("servletName")方法将返回Object您需要转换为ArrayList
ArrayList<Category> list =new ArrayList<Category>();
//storing passed value from jsp
list = (ArrayList<Category>)request.getAttribute("servletName");
回答by Prabhakaran Ramaswamy
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 listand the categoryin jsp. try this.
可能的错误是...
1.您从会话中的servelt 设置数组列表，而不是在请求中。
2.你设置的数组为空。
3.您重定向页面而不是转发页面。
您也不应该 在 jsp 中初始化list和category。尝试这个。
for(Category cx: ((ArrayList<Category>)request.getAttribute("servletName"))) {
out.println( cx.getId());
out.println(cx.getName());
out.println(cx.getMainCategoryId() );
}
回答by Pradeep Angre
here list attribute name set in request request.setAttribute("List",list);and ArrayList list=new ArrayList();
这里列出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));
}
%>
回答by Ralph Weber
<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>
回答by Ralph Weber
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();
}
}
