java.lang.ClassCastException：无法将java.lang.String强制转换为com.security.model.UserRequest

Question

Am retriving UserRequest object from DB using JPA Query as following.

@Query("SELECT req.supervisorEmail from User u, UserRequest as req WHERE u.username = req.userRequestName and req.userRequestRole= '4' and u.active=true")
 public List<UserRequest> getSupervisorEmailIds();

Am having the UserRequest POJO class as follows.

public class UserRequest implements Identifiable<Long>, LazilyLoadable {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@JsonIgnore
private Long id;

@Column(name = "supervisor_email")
private String supervisorEmail;

@Column(name="user_request_name")
private String userRequestName;

@Column(name="user_request_role")
private String userRequestRole;

}

when am trying to iterating over the UserRequest object am getting the ClassCastException for the below code.

List<UserRequest> supervisorEmailIds = userService.getSupervisorEmailIds();
for(UserRequest s: supervisorEmailIds) { // throwing exception on this line.
if(s!=null) {
System.out.println("Printing -->"+s.getSupervisorEmail());
}
System.out.println("Null error");
}

Following is the error am getting.

2019-02-22 00:34:26,719 [http-9191-1] ERROR         com.cat.pscs.api.controller.BaseController:  83 - Unhandled exception while processing request for URL : http://localhost:9191/security/users/get-supervisor-emailids with exception : java.lang.String cannot be cast to com.cat.pscs.security.model.UserRequest

java.lang.ClassCastException: java.lang.String cannot be cast to com.cat.pscs.security.model.UserRequest at com.cat.pscs.security.controller.UserController.getSupervisorEmailIds(UserController.java:320)

Answer 1

Are you sure that below line returns UserRequestList? I think it returns list of strings

List<UserRequest> supervisorEmailIds = userService.getSupervisorEmailIds();

just change your sql query that returns list of UserRequest object .

Answer 2

Your query returns list of String , while you expect to get list of UserRequest . Changing query as follow should do the job:

@Query("SELECT req from User u, UserRequest as req WHERE u.username = req.userRequestName and req.userRequestRole= '4' and u.active=true")

Answer 3

Inside @Query you wrote

SELECT req.supervisorEmail from User u, UserRequest as req...

I suppose supervisorEmail is a VARCHAR or CHAR table column.
You're extracting only a single String column.

If you want UserRequest (s), you need

SELECT req from User u, UserRequest as req...