Question

我是Spring的新手。当我试图查看localhost:8080/persons时，我收到错误

java.lang.NullPointerException: null 
at by.bsuir.task.service.PersonServiceImpl.listPersons(PersonServiceImpl.java:32) ~[classes/:na] 
at by.bsuir.task.controller.PersonController.listPersons(PersonController.java:31) ~[classes/:na] 
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na] 
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na] 
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na] 
at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na] 
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE] 
at ...

我认为问题出在PersonDAOImpl，方法listPersons（），session得到NPE。但我不确定。我的项目如下：

PersonServiceImpl

package by.bsuir.task.service; 

import java.util.List; 

import org.springframework.stereotype.Service; 
import org.springframework.transaction.annotation.Transactional; 

import by.bsuir.task.dao.PersonDAO; 
import by.bsuir.task.model.Person; 

"personService" 
public class PersonServiceImpl implements PersonService { 

private PersonDAO personDAO; 

public void setPersonDAO(PersonDAO personDAO) { 
this.personDAO = personDAO; 
} 

@Transactional 
public void addPerson(Person p) { 
this.personDAO.addPerson(p); 
} 

@Transactional 
public void updatePerson(Person p) { 
this.personDAO.updatePerson(p); 
} 

@Transactional 
public List<Person> listPersons() { 
return this.personDAO.listPersons(); 
} 

@Transactional 
public Person getPersonById(int id) { 
return this.personDAO.getPersonById(id); 
} 

@Transactional 
public void removePerson(int id) { 
this.personDAO.removePerson(id); 
} 

}

PersonDAOImpl

package by.bsuir.task.dao; 

import java.util.List; 

import org.hibernate.Session; 
import org.hibernate.SessionFactory; 
import org.slf4j.Logger; 
import org.slf4j.LoggerFactory; 
import org.springframework.stereotype.Repository; 

import by.bsuir.task.model.Person; 

@Repository 
public class PersonDAOImpl implements PersonDAO { 

private static final Logger logger = LoggerFactory.getLogger(PersonDAOImpl.class); 

private SessionFactory sessionFactory; 

public void setSessionFactory(SessionFactory sf){ 
this.sessionFactory = sf; 
} 

public void addPerson(Person p) { 
Session session = this.sessionFactory.getCurrentSession(); 
session.persist(p); 
logger.info("Person saved successfully, Person Details="+p); 
} 

public void updatePerson(Person p) { 
Session session = this.sessionFactory.getCurrentSession(); 
session.update(p); 
logger.info("Person updated successfully, Person Details="+p); 
} 

"unchecked" 
public List<Person> listPersons() { 
Session session = this.sessionFactory.getCurrentSession(); 
List<Person> personsList = session.createQuery("from Person").list(); 
for(Person p : personsList){ 
logger.info("Person List::"+p); 
} 
return personsList; 
} 

public Person getPersonById(int id) { 
Session session = this.sessionFactory.getCurrentSession(); 
Person p = (Person) session.load(Person.class, new Integer(id)); 
logger.info("Person loaded successfully, Person details="+p); 
return p; 
} 

public void removePerson(int id) { 
Session session = this.sessionFactory.getCurrentSession(); 
Person p = (Person) session.load(Person.class, new Integer(id)); 
if(null != p){ 
session.delete(p); 
} 
logger.info("Person deleted successfully, person details="+p); 
} 

}

PersonController

package by.bsuir.task.controller; 

import java.util.List; 

import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.beans.factory.annotation.Qualifier; 
import org.springframework.stereotype.Controller; 
import org.springframework.ui.Model; 
import org.springframework.web.bind.annotation.ModelAttribute; 
import org.springframework.web.bind.annotation.PathVariable; 
import org.springframework.web.bind.annotation.RequestMapping; 
import org.springframework.web.bind.annotation.RequestMethod; 

import by.bsuir.task.model.Person; 
import by.bsuir.task.service.PersonService; 

@Controller 
public class PersonController { 

@Autowired 
private PersonService personService; 

required=true 
@Qualifier(value = "personService") 
public void setPersonService(PersonService ps){ 
this.personService = ps; 
} 

value = "/persons", method = RequestMethod.GET 
public String listPersons(Model model) { 
List<Person> listOfUsers = this.personService.listPersons(); 
model.addAttribute("person", new Person()); 
model.addAttribute("listPersons", listOfUsers); 
return "person"; 
} 

//For add and update person both 
value= "/person/add", method = RequestMethod.POST 
public String addPerson(@ModelAttribute("person") Person p){ 

if(p.getId() == 0){ 
//new person, add it 
this.personService.addPerson(p); 
}else{ 
//existing person, call update 
this.personService.updatePerson(p); 
} 

return "redirect:/persons"; 

} 

"/remove/{id}" 
public String removePerson(@PathVariable("id") int id){ 

this.personService.removePerson(id); 
return "redirect:/persons"; 
} 

"/edit/{id}" 
public String editPerson(@PathVariable("id") int id, Model model){ 
model.addAttribute("person", this.personService.getPersonById(id)); 
model.addAttribute("listPersons", this.personService.listPersons());
return "person"; 
} 

}

似乎无法找到我的问题，我只是在学习Spring \ Hibernate

Answer 1

您的问题中缺少一些代码。

对于班级PersonServiceImpl，代码应如下所示：

@Service("personService") 
public class PersonServiceImpl implements PersonService { 

    @Autowired     
    private PersonDAO personDAO; 
    // Some other code
}

将@Autowired注释添加到PersonDAO类而不这样做会导致NullPointerException，因为您没有为该类创建任何对象，使用@Autowired注释它将告诉{{1}}需要注射的春天。

调用sessionFactory.getCurrentSession（）时返回nullPointerException

1 个答案: