Spring boot java.lang.NullPointerException: null

Question

I am trying to build Spring-boot CRUD application with Hibernate and REST -API.However when I try to run the app everything is working fine but console is displaying the following error

java.lang.NullPointerException: null
    at io.javabrains.EmployerController.getAllEmployers(EmployerController.java:20) ~[classes/:na]

I tried to change the value however it didnt work

EmployerService.java

package io.javabrains;

import java.util.ArrayList;
import java.util.List;

import org.springframework.stereotype.Service;

import io.javabrains.Entity.Employer;

@Service
public class EmployerService {

    private Repository repository;

    public List<Employer>getAllEmployers(){
        List<Employer>employers = new ArrayList<>();
        repository.findAll()
        .forEach(employers::add);
        return employers;

    }

    public void addEmployer(Employer employer) {
        repository.save(employer);
    }    
}

EmployerController.java

package io.javabrains;

import java.util.List;

import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import io.javabrains.Entity.Employer;

@RestController
public class EmployerController {

    private EmployerService service;


     @RequestMapping("/employer") 
     public List<Employer>getAllEmployers()
     {
         return  service.getAllEmployers();
}
    /*
     * @RequestMapping("/employer/{id}") public Employer getEmployer(@PathVariable
     * int id) { return service.getEmployer(id); }
     */

    @RequestMapping(method=RequestMethod.POST,value="/employer/create")
    public void addEmployer(@RequestBody Employer employer) {
        service.addEmployer(employer);  
    }
}

....

Answer 1

On the analysis of the code snippet given, the null pointer exception occurred since your code doesn't ask the spring dependency injector to inject EmployerService as a dependency to EmployerController, so it doesn't inject the EmployerService bean class to the reference private EmployerService employerService; thus it is null in EmployerController. You can ask Spring Dependency Injector to inject dependency by adding @Autowire annotation private EmployerService service; refence in EmployerController

Update your EmployerService to the following will work

package io.javabrains;

import java.util.List;

import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import io.javabrains.Entity.Employer;

@RestController
public class EmployerController {

  //UPDATE : Autowiring
  @Autowired
  private EmployerService employerService;


  @RequestMapping("/employer")
  public List < Employer > getAllEmployers() {
    return service.getAllEmployers();
  }
  /*
   * @RequestMapping("/employer/{id}") public Employer getEmployer(@PathVariable
   * int id) { return employerService.getEmployer(id); }
   */

  @RequestMapping(method = RequestMethod.POST, value = "/employer/create")
  public void addEmployer(@RequestBody Employer employer) {
    employerService.addEmployer(employer);
  }
}

And Also, the same issue would occur in Service when trying to access repository.

Update EmployeeService.java code include @autorwired logic:

package io.javabrains;

import java.util.ArrayList;
import java.util.List;

import org.springframework.stereotype.Service;
import org.springframework.beans.factory.annotation.Autowired;

import io.javabrains.Entity.Employer;

@Service
public class EmployerService {

    @Autowired
    private Repository repository;

    public List<Employer>getAllEmployers(){
        List<Employer>employers = new ArrayList<>();
        repository.findAll()
        .forEach(employers::add);
        return employers;

    }

    public void addEmployer(Employer employer) {
        repository.save(employer);
    }    
}