java.lang.NullPointerException error on accessing page linked to controller class - spring

Question

I am running a spring mvc application with classes annotated as #controller,#service,#component and for the view layer thymeleaf is used. However on navigating to the path localhost:8080/owners no owner data is displayed.Looks like even though data is getting saved in owner object but ownerservicemap is null for no reason.
Below is the error
Owner data is loaded
2019-06-26 12:39:47.237 INFO 5776 --- [ restartedMain]
.ConditionEvaluationDeltaLoggingListener : Condition evaluation
unchanged
2019-06-26 12:39:50.475 INFO 5776 --- [nio-8080-exec-1]
o.a.c.c.C.[Tomcat-1].[localhost].[/] : Initializing Spring
DispatcherServlet 'dispatcherServlet'
2019-06-26 12:39:50.475 INFO 5776 --- [nio-8080-exec-1]
o.s.web.servlet.DispatcherServlet : Initializing Servlet
'dispatcherServlet'
2019-06-26 12:39:50.483 INFO 5776 --- [nio-8080-exec-1]
o.s.web.servlet.DispatcherServlet : Completed initialization in
8 ms
2019-06-26 12:39:50.507 ERROR 5776 --- [nio-8080-exec-1]
o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for
servlet [dispatcherServlet] in context with path [] threw exception
[Request processing failed; nested exception is
java.lang.NullPointerException] with root cause
java.lang.NullPointerException: null
at com.example.Project.controllers.OwnerController.listOwners(OwnerController.java:33)
~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_211]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
~[na:1.8.0_211]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
~[na:1.8.0_211]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_211]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
DataLoader class to load the data
#Component public class DataLoader implements CommandLineRunner{
private final OwnerService ownerService;
public DataLoader()
{
ownerService=new OwnerServiceMap();
}
#Override
public void run(String... args) throws Exception {
// TODO Auto-generated method stub
Owner owner1=new Owner();
owner1.setId(1L);
owner1.setFirstName("ally");
owner1.setLastName("nilson");
Owner sa1=ownerService.save(owner1);
}}
Below is the ownercontroller class
#RequestMapping("/owners") #Controller public class OwnerController {
private OwnerService ownerservice;
#Autowired
public OwnerController(OwnerService ownerservice)
{
this.ownerservice=ownerservice;
}
#RequestMapping({"","/","/index","/index.html"})
public String listOwners(Model model)
{
model.addAttribute("owner",ownerservice.findAll());// System.out.println(ownerservice.findById(1L).getLastName());
return "owner/index";
}}
OwnerService interface
public interface OwnerService extends CrudService<Owner, Long>{
Owner findByLastName(String lastname);}
AbstractmapService class
public abstract class AbstractMapService<T,ID> {
protected Map<ID,T> map=new HashMap<>();
Set<T> findAll()
{
return new HashSet<>(map.values());
}
T findById(ID id)
{
return map.get(id);
}
T save(ID id,T object)
{
map.put(id, object);
return object;
}
void deleteById(ID id)
{
map.remove(id);
}
void delete(T object)
{
map.entrySet().removeIf(entry->entry.getValue().equals(object));
}}
OwnerServiceMap class
#Service public class OwnerServiceMap extends AbstractMapService<Owner,Long>implements OwnerService{
#Override
public Set<Owner> findAll() {
// TODO Auto-generated method stub
return super.findAll();
}
#Override
public Owner findById(Long id) {
// TODO Auto-generated method stub
return super.findById(id);
}
#Override
public Owner save(Owner object) {
// TODO Auto-generated method stub
return super.save(object.getId(),object);
}
#Override
public void delete(Owner object) {
// TODO Auto-generated method stub
super.delete(object);
}
#Override
public void deleteById(Long id) {
// TODO Auto-generated method stub
super.deleteById(id);
}
#Override
public Owner findByLastName(String lastname) {
// TODO Auto-generated method stub
return null;
}
}

Answer 1

#Service
public class OwnerServiceMap extends AbstractMapService<Owner,Long> implements OwnerService{ ... // }
To be autowired, you must register with the bean.
EDIT1
You did to save another service's Map.
#Component public class DataLoader implements CommandLineRunner{
private final OwnerService ownerService;
public DataLoader()
{
ownerService=new OwnerServiceMap();
}
// ...
And here,
#RequestMapping("/owners") #Controller public class OwnerController {
private OwnerService ownerservice;
#Autowired
public OwnerController(OwnerService ownerservice)
{
this.ownerservice=ownerservice;
}
check this please.
EDIT2
If you register Object to bean, container has that by singleton object.
then, Using #Autowired get singleton object from container.
NOTE : it's different with GOF's singleton.
To summarize, what you use with the new keyword like ownerService=new OwnerServiceMap(); was to create a new instance, not to use the bean instance that you assigned to the Container. So, using the different instances, the above problem occurs.