在Spring中使用多线程时出现NullPointer异常

Question

我是多线程的新手。我试图使用crud存储库在sql数据库中保存一个对象列表。但是我在保存操作中得到了null指针异常。下面是我的代码和异常。线程级

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();
}
}
}

服务等级

@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> {
}

我得到了exeptionpresRepo.save(pres(；

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，只说

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

它运行良好，我可以将它保存到数据库中。但我想实现线程。提前谢谢。

Answer 1

由于这里：

private MedicineService medServ = new MedicineService();

实例"medServ"是春季IOC管理，如果你"新建"它，可能不会得到"处方库"的实例，因为它是"@Autowire"，当你调用presRepo.save(pres)时，它将抛出NPE。但如果你不使用线程，就意味着没有一个实例是你自己新的，所以它可以很好地工作

Answer 2

我如下修改了我的线程类，我能够获得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();
}
}
}