java - 使用 JPA 将对象上传到数据库时出现 NULL 指针异常

Question

在我的代码中，我读取了 Excel 工作表并将读取的参数从 Excel 工作表传递给方法

@RestController
@RequestMapping("/api/v1")
public class ExcelController3 {

    private MultipartFile uploadfile;

    @Autowired
   private EmployeeRepository employeeRepository;


    @RequestMapping(value = "/upload3", method = RequestMethod.POST, consumes = javax.ws.rs.core.MediaType.MULTIPART_FORM_DATA)
    public void uploadFileHandler(@RequestParam("name") String name,
                                  @RequestParam("file") MultipartFile file) throws IOException {


        this.uploadfile=file;
        System.out.println("*****************************");

        System.out.println("file.getOriginalFilename() " + file.getOriginalFilename());
        System.out.println("file.getContentType()" + file.getContentType());
        System.out.println("file.getInputStream() " + file.getInputStream());
        System.out.println("file.toString() " + file.toString());
        System.out.println("file.getSize() " + file.getSize());
        System.out.println("name " + name);
        System.out.println("file.getBytes() " + file.getBytes());
        System.out.println("file.hashCode() " + file.hashCode());
        System.out.println("file.getClass() " + file.getClass());
        System.out.println("file.isEmpty() " + file.isEmpty());


        try {
            ExcelController ex=new ExcelController();
            File f1=ex.convert(file);
       //     FileInputStream file = new FileInputStream(new File("E://Imp/Details.xlsx"));
            XSSFWorkbook workbook = new XSSFWorkbook(f1);
            XSSFSheet sheet = workbook.getSheetAt(0);
            Iterator<Row> rowIterator = sheet.iterator();
            rowIterator.next();
            while(rowIterator.hasNext())
            {
                Row row = rowIterator.next();
                //For each row, iterate through each columns
                Iterator<Cell> cellIterator = row.cellIterator();

                while(cellIterator.hasNext())
                {
                    Cell cell = cellIterator.next();
                    //This will change all Cell Types to String
                    cell.setCellType(Cell.CELL_TYPE_STRING);
                    switch(cell.getCellType())
                    {
                        case Cell.CELL_TYPE_BOOLEAN:
                            System.out.println("boolean===>>>"+cell.getBooleanCellValue() + "\t");
                            break;
                        case Cell.CELL_TYPE_NUMERIC:

                            break;
                        case Cell.CELL_TYPE_STRING:

                            List list=new ArrayList();
                            list.add(cell.getStringCellValue());

                            break;
                    }


                }
                name=row.getCell(0).getStringCellValue();
                String empid = row.getCell(1).getStringCellValue();
               String add=row.getCell(2).getStringCellValue();
              String  mobile=row.getCell(3).getStringCellValue();
                System.out.println(name+empid+add+mobile);
                ExcelController3 ex1=new ExcelController3();
             //   ex1.InsertRowInDB(name,empid,add,mobile);

                System.out.println("");
                Employee em=new Employee();

                em.setName(name);
                em.setEmpid(empid);
                em.setAddress(add);
                em.setMobile(mobile);
                System.out.println(em);
                System.out.println(em.getAddress());
                System.out.println(em.getEmpid());
                System.out.println(em.getMobile());
                System.out.println(em.getName());
                ex1.InsertRowInDB(name,empid,add,mobile,em);

            }
            workbook.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InvalidFormatException e) {
            e.printStackTrace();
        }
    }
    public void InsertRowInDB(String name,String empid,String add,String mobile,Employee em) {

//        System.out.println("name "+name);
//        System.out.println("empid "+empid);
//        System.out.println("add "+add);
//        System.out.println("mobile "+mobile);
//        Employee em=new Employee();
//
//        em.setName(name);
//        em.setEmpid(empid);
//        em.setAddress(add);
//        em.setMobile(mobile);
//        System.out.println(em);
//        System.out.println(em.getAddress());
//        System.out.println(em.getEmpid());
//        System.out.println(em.getMobile());
//        System.out.println(em.getName());


     employeeRepository.save(em);

//employeeRepository.save(em);
//        Statement stmt=db.con.createStatement();
//        PreparedStatement ps=null;
//        String sql="Insert into Employee(Name,EmployeeId,Address,ContactInfo) values(?,?,?,?)";
//        ps=db.con.prepareStatement(sql);
//        ps.setString(1, name);
//        ps.setString(2, empid);
//        ps.setString(3, add);
//        ps.setString(4, mobile);
//        ps.executeUpdate();

        System.out.println("Values Inserted Successfully");
    }



    public File convert(MultipartFile file) throws IOException {
        File convFile = new File(file.getOriginalFilename());
        convFile.createNewFile();
        FileOutputStream fos = new FileOutputStream(convFile);
        fos.write(file.getBytes());
        fos.close();
        return convFile;
    }


    @GetMapping(value="/upload")
    public ResponseEntity<Collection<Employee>> getallemployees(){
        Collection<Employee> el =employeeRepository.findAll();
        return new ResponseEntity<Collection<Employee>>(el, HttpStatus.OK);
    }
}

但它在 employeeRepository.save(em); 给了我空指针异常。无法找出我还自动连接了employeeRepository并为jpa创建了正确的pojo类的原因。

Answer 1

因此，再次阅读您的代码后，问题是因为您在 Controller 上使用了一些"new"内容。此:ExcelController3 ex1=new ExcelController3();创建非托管的ExcelController3的全新实例(即没有@Autowired 或任何其他 spring magic)，因此 ex1 的存储库为空。

您可能想要替换:

ExcelController3 ex1=new ExcelController3();
ex1.InsertRowInDB(name,empid,add,mobile,em);

由

this.InsertRowInDB(name,empid,add,mobile,em);

另请注意，您不应该不在 Controller 上存储某些上传的文件(private MultipartFile uploadfile;)(因为每个用户都使用相同的 Controller 实例)

<小时/>

一些阅读:

• http://docs.spring.io/spring/docs/current/spring-framework-reference/html/beans.html
• http://www.oracle.com/technetwork/java/codeconventions-135099.html