Issue
So, I have struggled for 2 days to understand what my error is. My drop down list is not populating with data from the database. I am using Java EE and MySQL.
I can insert data in the database without a problem but when i retrieve it for some reason the jsp doesn't do its thing correctly so that I always get the drop down empty. This is the table I am using:
create table category(
category_id int auto_increment,
name varchar(30),
primary key(category_id)
);
This is the servlet I am using and the method for executing the query. As you can see I am returning a List of objects and then I am adding it as a request attribute in the doGet method. So I guess until here everything should work fine.
public class DropDownServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException {
try {
List<Category> categories = retrieveCategories();
request.setAttribute("categories", categories);
RequestDispatcher view = request.getRequestDispatcher("viewdropdown.jsp");
view.forward(request, response);
} catch (ClassNotFoundException | SQLException | IOException ex) {
ex.printStackTrace();
}
}
public static List<Category> retrieveCategories() throws ClassNotFoundException, SQLException {
Connection conn = DatabaseConnection.initializeConnection();
String query = "Select * from category";
PreparedStatement pstmnt = conn.prepareStatement(query);
List<Category> categories = new ArrayList<>();
ResultSet rs = pstmnt.executeQuery();
while (rs.next()) {
int id = rs.getInt("category_id");
String name = rs.getString("name");
Category cat = new Category(id,name);
categories.add(cat);
}
conn.close();
return categories;
}
and here is the jsp with the dropdown which doesn't display the data that it should.
<html>
<head>
<title>Dropdown page</title>
</head>
<body>
<h1>The names of the categories are the following:</h1>
<select id ="dropdown">
<c:forEach items="${categories}" var="category">
<option value = "${category.name}">${category.name}</option>
</c:forEach>
</select>
<br>
<br>
</body>
</html>
EDIT: So I have created this hardcoded test method to test my code and I add it as request parameter identically to how I added the other method with the DB query. My DropDown is still empty, so the problem could be from the way I try to display the items in the jsp. I think it could be in the loop I have.
public static List<Category> testMethod(){
List<Category> list = new ArrayList<>();
Category one = new Category(1,"Blue");
Category two = new Category(2,"Red");
list.add(one);
list.add(two);
return list;
}
Solution
Looks like the ${categories} is an empty collection.
First, make sure, you have imported the JSTL Core library into your JSP page. This is done by putting
<%@ taglib prefix="c" uri = "http://java.sun.com/jsp/jstl/core" %>
at the top of the JSP page.
Additionally, you can check on the JSP side if the collection is empty by adding somewhere:
<c:out value="${categories.size()}" />.
Also, you are using Expression Language directly between the HTML <option> tags, so you will also need adding:
<%@ page isELIgnored = "false" %>
at the top of the JSP page to make it evaluable to the appropriate value, instead of rendering plain text.
Answered By - ptr92zet
Answer Checked By - Clifford M. (JavaFixing Volunteer)
