Spring Boot java.lang.NullPointerException：空

在分析给定的代码片段时，发生空指针异常，因为您的代码没有要求spring依赖注入器将其注入EmployerService为对的依赖EmployerController，因此它没有将EmployerServicebean类注入到引用中，private EmployerService employerService;因此in中为null EmployerController。您可以通过在中添加@Autowire注释private EmployerService service;引用来要求Spring Dependency Injector注入依赖项。EmployerController

更新您EmployerService的以下内容即可

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);
  }
}

并且，Service尝试访问时也会发生相同的问题repository。

更新EmployeeService.java代码包括@autorwired逻辑：

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);
    }    
}