How can I fix duplicated folders in the path while accessing the page?

Question

I have the technical question related to the issue as:

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Thu Jan 12 13:49:28 CET 2023
There was an unexpected error (type=Not Found, status=404).
JSP file [/admin/project_category/admin/project_category/list.jsp] not found

with accessing the page http://localhost:8080/admin/project_category/list.

While debugging controller:

@GetMapping("admin/project_category/list")
public ModelAndView projectCategoryList() { 
  List<Project> projectList = projectServiceImpl.get(); 
  ModelAndView modelAndView = new ModelAndView("admin/project_category/list"); 
  modelAndView.addObject("projectList", projectList); 
  return modelAndView; 
}

inside the project, I don't have any duplicated folders:

but using the browser will be another situation:

There's I see I need additional resolver, but in the following project I don't need to use any specific resolvers.

I don't quite understand, why I don't have it twice in similar project.

Can someone tell me, please, what do I need to fix to handle this problem finally? Is it the problem with JSP files specifically or something?

Thank you in advance for any helpful ideas.

UPD:

After some observation, I see:

if I have the following snippet of code:

@GetMapping("admin/project_category/list")
public ModelAndView projectCategoryList() {
    List<Project> projectList = projectServiceImpl.get();
    ModelAndView modelAndView = new ModelAndView("admin/project_category/list");
    modelAndView.addObject("projectList", projectList);
    return modelAndView;
}

I'm getting the issue as:

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.
Thu Jan 12 13:49:28 CET 2023 There was an unexpected error (type=Not Found, status=404). JSP file [/admin/project_category/admin/project_category/list.jsp] not found

If I add slash in the beginning as:

@GetMapping("/admin/project_category/list")
public ModelAndView projectCategoryList() {
    List<Project> projectList = projectServiceImpl.get();
    ModelAndView modelAndView = new ModelAndView("/admin/project_category/list");
    modelAndView.addObject("projectList", projectList);
    return modelAndView;
}

I'm getting another issue as:

There was an unexpected error (type=Internal Server Error, status=500).
Cannot invoke "java.util.List.iterator()" because "projectCategory" is null java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "projectCategory" is null

Answer 1

1. To fix the issue:

Fri Jan 13 23:16:50 CET 2023 There was an unexpected error (type=Internal Server Error, status=500). Cannot invoke "java.util.List.iterator()" because "projectCategory" is null java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "projectCategory" is null

I needed to change the parameter projectCategory instead of projectList:

@GetMapping("/admin/project_category/list")
public ModelAndView projectCategoryList() { 
   List<Project> projectList = projectServiceImpl.get();    
   ModelAndView modelAndView = 
   new ModelAndView("/admin/project_category/list"); 
   modelAndView.addObject("projectList", projectList);
   return modelAndView; 
}

as the following:

@GetMapping("/admin/project_category/list")
public ModelAndView projectCategoryList() { 
   List<Project> projectList = projectServiceImpl.get(); 
   ModelAndView modelAndView = new 
   ModelAndView("/admin/project_category/list"); 
   modelAndView.addObject("projectCategory", projectList); 
   return modelAndView; 
}

2. To fix the issue with duplicated folders in the path:

Whitelabel Error Page This application has no explicit mapping for /error, so you are seeing this as a fallback. Sat Jan 14 00:01:17 CET 2023 There was an unexpected error (type=Not Found, status=404). JSP file [/admin/project_category/admin/project_category/list.jsp] not found

you need to add slash in the beginning of mapping declaration:

@GetMapping("admin/project_category/list")
public ModelAndView projectCategoryList() { 
List<Project> projectList = projectServiceImpl.get(); 
   ModelAndView modelAndView = new 
   ModelAndView("admin/project_category/list"); 
   modelAndView.addObject("projectCategory", projectList); 
   return modelAndView;
}

as the following:

@GetMapping("/admin/project_category/list")
public ModelAndView projectCategoryList() {
    List<Project> projectList = projectServiceImpl.get();
    ModelAndView modelAndView = new 
    ModelAndView("/admin/project_category/list");
    modelAndView.addObject("projectCategory", projectList);
    return modelAndView;
}

3. To fix the issue:

Whitelabel Error Page This application has no explicit mapping for /error, so you are seeing this as a fallback. Sat Jan 14 00:22:21 CET 2023 There was an unexpected error (type=Internal Server Error, status=500). class com.test.application.data.models.Project cannot be cast to class com.test.application.data.models.ProjectCategory (com.test.application.data.models.Project and com.test.application.data.models.ProjectCategory are in unnamed module of loader org.springframework.boot.devtools.restart.classloader.RestartClassLoader u/6ef9aa30) java.lang.ClassCastException: class com.test.application.data.models.Project cannot be cast to class com.test.application.data.models.ProjectCategory (com.test.application.data.models.Project and com.test.application.data.models.ProjectCategory are in unnamed module of loader org.springframework.boot.devtools.restart.classloader.RestartClassLoader u/6ef9aa30)

I needed to change to the correct type inside list.jsp:

<tbody>
            <%
                List<ProjectCategory> projectCategory = (List<ProjectCategory>) request.getAttribute("projectCategory");
                for (ProjectCategory c : projectCategory)
                {
            %>
            <tr>
                <th scope="row"><%=c.getId()%></th>
                <td><%=c.getName()%></td>
                <td>
                    <a class="btn btn-success" href="update?id=<%=c.getId()%>" role="button">Edit</a>
                    <a onclick="return confirm('Are you sure you want to delete it?');" class="btn btn-danger" href="delete?id=<%= c.getId() %>" role="button">Delete</a>
                </td>
            </tr>
            <%
                }
            %>
</tbody>

to another type of List as:

<tbody>
            <%
                List<Project> projectCategory = (List<Project>) request.getAttribute("projectCategory");
                for (Project c : projectCategory)
                {
            %>
            <tr>
                <th scope="row"><%=c.getId()%></th>
                <td><%=c.getName()%></td>
                <td>
                    <a class="btn btn-success" href="update?id=<%=c.getId()%>" role="button">Edit</a>
                    <a onclick="return confirm('Are you sure you want to delete it?');" class="btn btn-danger" href="delete?id=<%= c.getId() %>" role="button">Delete</a>
                </td>
            </tr>
            <%
                }
            %>
</tbody>

Answer 2

Try the following:

@GetMapping("admin/project_category/list")
public ModelAndView projectCategoryList(Map<String, Object> model) { 
  List<Project> projectList = projectServiceImpl.get(); 
  //ModelAndView modelAndView = new ModelAndView("admin/project_category/list"); 
  //modelAndView.addObject("projectList", projectList); 
  model.put("projectList", projectList);
  //return modelAndView; 
  return new ModelAndView("list");
}