在 Spring 中使用多线程时出现 NullPointer 异常

Question

我是多线程新手。我试图使用 crud 存储库在 sql 数据库中保存一个对象列表。但我在保存操作中遇到空指针异常。下面是我的代码和异常。线程 Class

public class PrescriptionThread implements Runnable{
  private MedicineService medServ = new MedicineService();
  private  Presciption pres ;

  public PrescriptionThread(Presciption pres) {
    this.pres = pres;
  }

  @Override
  public void run() {
    medServ.savePrescription(pres);
    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
  }
}

服务Class

@Service
public class MedicineService {

@Autowired
private PrescriptionRepository presRepo;

public void storePrescription(List<Presciption> payload) {

    ExecutorService executorService = Executors.newFixedThreadPool(5);
    for (Presciption presciption : payload) {
        Runnable runnable = new PrescriptionThread(presciption);
        executorService.execute(runnable);
    }
    executorService.shutdown();

    while(!executorService.isTerminated()) {}
}


public synchronized void savePrescription(Presciption pres) {
        presRepo.save(pres);
}
}

存储库

@Repository
public interface PrescriptionRepository extends CrudRepository<Presciption, Integer> {

}

我正在获得例外 presRepo.save(压力);

Exception in thread "pool-1-thread-3" Exception in thread "pool-1-thread-1" Exception in thread "pool-1-thread-2" java.lang.NullPointerException
at com.cerner.api.service.MedicineService.savePrescription(MedicineService.java:86)
at com.cerner.api.util.PrescriptionThread.run(PrescriptionThread.java:16)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)

如果我不使用线程而只说

for (Presciption presciption : payload) {
        presRepo.save(pres);
    }

它工作正常，我可以将它保存到数据库中。但是我想实现线程。提前致谢。

Answer 1

由于此处：

private MedicineService medServ = new MedicineService();

实例 'medServ' 是 spring IOC 管理，如果你 'new' 它，可能不会得到 'PrescriptionRepository' 的实例，因为它是 '@Autowire' , 当你调用 presRepo.save(pres) 时它会抛出 NPE。但是如果你不使用 Thread 意味着不是你自己新建的实例，所以它可以正常工作

Answer 2

我修改了我的线程 class 如下，我能够得到这个 bean。

public class PrescriptionThread implements Runnable{
private MedicineService medServ;// = new MedicineService();
private  Presciption pres ;

public PrescriptionThread(Presciption pres, MedicineService medicineService) {
this.pres = pres;
this.medServ = medicineService;
}

@Override
public void run() {
medServ.savePrescription(pres);
try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    e.printStackTrace();
}
}
}

在 Spring 中使用多线程时出现 NullPointer 异常

NullPointer exception while using Multithread in Spring

java

spring

multithreading

spring-annotations

threadpool