从普通类调用 JpaRepository 时如何修复 java.lang.NullPointerException？

Question

我是一名新的 Java 开发人员。我从普通类（不是主类，不在控制器中，..）调用 JpaRepository 并得到错误：

java.lang.NullPointerException
    at com.wecommit.criticalService.controller.TableSpaceWarningCRC.doTransData(TableSpaceWarningCRC.java:34)

这是我的代码： 普通班：

    package com.wecommit.criticalService.critical;

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

import com.wecommit.criticalService.entity.HistoryUpload;

public class CreateDataPerTable {

    HistoryUpload historyUpload;
    int l_historyUpload;

    @Autowired
    TableSpaceWarningCRC tableSpaceWarning;
    //Constructor
    public CreateDataPerTable(TableSpaceWarningCRC tableSpaceWarning) {
    }

    public void setHistoryUpload(HistoryUpload historyUpload) {
        //Get time_upload in historyUpload by historyUploadID

        this.historyUpload = historyUpload;
        l_historyUpload = historyUpload.getId();
    }   

    public void creatDataTables() {
//the error row bellow
            tableSpaceWarning.setTableSpaceWarningCRC(historyUpload);
            tableSpaceWarning.doTransData();


    }

}

并且类调用JpaRepository方法：

package com.wecommit.criticalService.critical;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
import com.wecommit.criticalService.entity.TableSpace;
import com.wecommit.criticalService.repository.TableSpaceRepository;
import com.wecommit.criticalService.entity.HistoryUpload;

@Component
public class TableSpaceWarningCRC {
    HistoryUpload historyUpload;

    @Autowired
    TableSpaceRepository tableSpaceRepository;

        public TableSpaceWarningCRC() {
    }

    public void setTableSpaceWarningCRC(HistoryUpload historyUpload) {
        this.historyUpload = historyUpload;
    }
    public void doTransData() {
        //TableSpace Data
        List<TableSpace> listTableSpace;
        listTableSpace = tableSpaceRepository.findByLogFileId(historyUpload.getLogFileId());
            for (int i = 0; i < listTableSpace.size(); i++) {
                TableSpaceWarningCreateTableData tableSpaceWarningCreateTableData = new TableSpaceWarningCreateTableData(listTableSpace.get(i),historyUpload.getLogFileId());
            }
    }
}

我添加了许多符号，但它不起作用。请帮我。 感谢阅读

Answer 1

您的类 TableSpaceWarningCRC 似乎不是 spring bean。自动布线仅适用于 spring 管理的类。

尝试在 TableSpaceWarningCRC 类的顶部添加 @Component 注释，然后从应用程序上下文中实例化该类，而不是调用构造函数。

How to get bean using application context in spring boot

此外，默认情况下，spring bean 是单例的。因此，如果您的类是有状态的或需要多个实例，请在 bean 定义中使用原型范围

https://www.baeldung.com/spring-inject-prototype-bean-into-singleton