java Spring数据JPA空指针异常

Question

enter image description here我是Spring Boot数据JPA存储库的新手。这是我第一次申请JPA。我正试图从数据库中获取数据。但返回空值

实体文件

import javax.persistence.*;

@Entity
@Table(name = "TASK_DETAILS")
public class TaskDetails {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "TASK_DETAILS_ID")
private long taskDetailsId;

@Column(name = "TASK_NAME")
private String TaskName;

@Column(name = "TASK_POLLING_TIME")
private int TaskTime;

@Column(name = "TASK_FILE")
private String TaskClassFile;

@Column(name = "TASK_STATUS")
private String TaskStatus;

public long getTaskDetailsId() {
return taskDetailsId;
}

public void setTaskDetailsId(long taskDetailsId) {
this.taskDetailsId = taskDetailsId;
}

public String getTaskName() {
return TaskName;
}

public void setTaskName(String taskName) {
TaskName = taskName;
}

public int getTaskTime() {
return TaskTime;
}

public void setTaskTime(int taskTime) {
TaskTime = taskTime;
}

public String getTaskClassFile() {
return TaskClassFile;
}

public void setTaskClassFile(String taskClassFile) {
TaskClassFile = taskClassFile;
}

public String getTaskStatus() {
return TaskStatus;
}

public void setTaskStatus(String taskStatus) {
TaskStatus = taskStatus;
}
}

存储库文件

import java.util.Collection;
import java.util.List;
import java.util.Optional;

@Repository
public interface TaskDetailsRepository extends JpaRepository<TaskDetails, String> {

TaskDetails findByTaskDetailsId(final long id);
}

我的主要方法

@Service
public class ImportAmazonData {

@Autowired
private TaskDetailsRepository taskDetailsRepositoryDAO;

public void getProductsFromAmazonStore(JobExecutionContext context) throws ClassNotFoundException {
final long taskID = (long) context.getJobDetail().getJobDataMap().get("taskId");

TaskDetails taskDetails = taskDetailsRepositoryDAO.findByTaskDetailsId(taskID);
System.out.println("Result : " + taskDetails.getTaskClassFile());
}
}

ProductSync文件

   import com.example.Schedular.AmazonSync.ImportAmazonData;
    import org.quartz.Job;
    import org.quartz.JobExecutionContext;
    import org.quartz.JobExecutionException;
    import org.springframework.stereotype.Component;

    public class ProductSync implements Job {

    @Autowired
    private ImportAmazonData importAmazonData;

    @Override
    public void execute(JobExecutionContext context) throws JobExecutionException {
        try {
            importAmazonData.getProductsFromAmazonStore(context);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

在这里，我试图通过id获取TaskDetails。但我的taskDetailsRepositoryDAO为空。这里我附上了我的错误日志。请告诉我。提前谢谢

错误日志

java.lang.NullPointerException: null
    at com.example.Schedular.AmazonSync.ImportAmazonData.getProductsFromAmazonStore(ImportAmazonData.java:20) ~[classes/:na]
    at com.example.Schedular.SyncData.ProductSync.execute(ProductSync.java:16) ~[classes/:na]
    at org.quartz.core.JobRunShell.run(JobRunShell.java:202) ~[quartz-2.3.2.jar:na]
    at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573) [quartz-2.3.2.jar:na]

Answer 1

在您的存储库文件中，即TaskDetails存储库应如下所示：

import java.util.Collection;
import java.util.List;
import java.util.Optional;

@Repository
public interface TaskDetailsRepository extends JpaRepository<TaskDetails, Long> {

Optional<TaskDetails> findByTaskDetailsId(Long id);
}

在域类中使用包装器而不是原语

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "TASK_DETAILS_ID")
private Long taskDetailsId;

如果您试图根据特定值查找记录，请指定该类型，即Long。 如果您的方法要从数据库返回sing记录，请始终使用Optional。这将帮助您解析空指针

这可能对你有帮助