java.lang.ClassCastException: java.util.HashMap cannot be cast to in spring boot microservice

Question

I am trying to fetch the matched string character by using spring data jpa query method and spring boot. When I am implementing this , I am getting the error like the following,

java.lang.ClassCastException: java.util.HashMap cannot be cast to com.spacestudy.model.RoomInvestigatorMapping

My service file containes the following code,

public List<String> retrieveReponsiblePerson(String sEmpName)
{
    List<RoomInvestigatorMapping> roomInvestigatorListResultObj = roomInvestigatorMappingRepositoryObj.findInvestigatorUsingName();

    List<String> roomInvestigatorListReturnObj = new ArrayList<>();

    for (RoomInvestigatorMapping result : roomInvestigatorListResultObj) 
    {
        String subStringRoomInvestigator = result.employee.sEmpName;
        if (subStringRoomInvestigator.contains(sEmpName)) 
        {
            List<String> obj = new ArrayList<>();
            obj.add(subStringRoomInvestigator);
            roomInvestigatorListReturnObj.addAll(obj);
        }
    }
    return roomInvestigatorListReturnObj;
}

And I am calling this method from controller file like the following,

@GetMapping("/loadResponsiblePersons")
public List<String> loadResponsiblePersonsMethod(
        @RequestParam(value = "sEmpName", required = true) String sEmpName) 
{
    return roomServiceObj.retrieveReponsiblePerson(sEmpName);
}

And my repository file containes the following,

@Repository
public interface RoomInvestigatorMappingRepository extends JpaRepository<RoomInvestigatorMapping, Integer>{

// find RoomInvestigatorMapping details by id
@Query(" select new map(emp.sEmpName as sEmpName, emp.nEmpId as nEmpId, "   
        + "roomInvest.nRoomInvestigatorMappingId as nRoomInvestigatorMappingId, "
        + "roomInvest.nRoomAllocationId as nRoomAllocationId) "
        + "from RoomInvestigatorMapping as roomInvest Inner Join Employee  as emp "
        + "on roomInvest.nInvestigatorId  = emp.nEmpId ")
List<RoomInvestigatorMapping> findInvestigatorUsingName();
}

Error stack like the following when I am calling the API,

java.lang.ClassCastException: java.util.HashMap cannot be cast to com.spacestudy.model.RoomInvestigatorMapping
at com.spacestudy.services.RoomService.retrieveReponsiblePerson(RoomService.java:210) ~[classes/:na]
at com.spacestudy.controller.RoomController.loadResponsiblePersonsMethod(RoomController.java:59) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_141]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_141]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_141]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_141]

My RoomInvestigatorMapping.java like the following,

@Entity
@Table(name="roominvestigatormapping")
public class RoomInvestigatorMapping implements Serializable
{

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY, generator = "roominvestigatormapping_seq_generator")
@SequenceGenerator(name = "roominvestigatormapping_seq_generator", sequenceName = "roominvestigatormapping_seq",allocationSize=1)

@Column(name="nroom_investigator_mapping_id",columnDefinition="serial")
public Integer nRoomInvestigatorMappingId;

@Column(name="nroom_allocation_id")
public Integer nRoomAllocationId;

@Column(name="ninvestigator_id")
public Integer nInvestigatorId;

@Min(0)
@Max(100)
@Column(name="npercentage_assigned")
public Integer nPercentageAssigned;

@Column(name="scomment")
public String scomment;

@ManyToOne(optional=true)
@JoinColumn(name="ninvestigator_id",referencedColumnName="nemp_id", insertable = false, updatable = false)
public Employee employee;

@ManyToOne(optional=true)
@JoinColumn(name="nroom_allocation_id", insertable = false, updatable = false)
public RoomDepartmentMapping roomDepartmentMapping; 

}

What is causing this error?

Answer 1

First, let's create constructors with parameters that you need for RoomInvestigatorMapping and Employee, then you should add these lines:

For RoomInvestigatorMapping

public RoomInvestigatorMapping() {
     // Empty constructor
}

public RoomInvestigatorMapping(String sEmpName, Integer nEmpId,
                               Integer nRoomInvestigatorMappingId,
                               Integer nRoomAllocationId) {
     this.employee = new Employee(sEmpName, nEmpId);
     this.nRoomInvestigatorMappingId = nRoomInvestigatorMappingId;
     this.nRoomAllocationId = nRoomAllocationId;                    
}

For Employee

public Employee() {
     // Empty constructor
}

public Employee(String sEmpName, Integer nEmpId) {
     this.sEmpName = sEmpName;
     this.nEmpId = nEmpId;
}

Second, let's modify your query like:

@Query("SELECT new com.spacestudy.model.RoomInvestigatorMapping(emp.sEmpName as sEmpName, emp.nEmpId as nEmpId,"   
     + " roomInvest.nRoomInvestigatorMappingId as nRoomInvestigatorMappingId,"
     + " roomInvest.nRoomAllocationId as nRoomAllocationId) "
     + "FROM RoomInvestigatorMapping as roomInvest "
     + "INNER JOIN Employee  as emp "
     + "ON roomInvest.nInvestigatorId  = emp.nEmpId ")
List<RoomInvestigatorMapping> findInvestigatorUsingName();

Answer 2

In your Repository interface @Query return a Map that is issue for class Casting.

you are selecting a new Map and expecting a RoomInvestigatorMapping entity that cannot done by Hibernate.

select new map(emp.sEmpName as sEmpName, emp.nEmpId as nEmpId, " + "roomInvest.nRoomInvestigatorMappingId as nRoomInvestigatorMappingId, " + "roomInvest.nRoomAllocationId as nRoomAllocationId)

The above query will return List<Map<String, Object>>.