字符串无法转换为DAO接收器

Question

我试图用列表对象执行批量插入操作但插入时我得到的字符串无法转换为DAO。迭代器循环中的接收器。

我试图列出列表对象，那时它是从列表中打印值。但是，当我使用泛型是正常列表它显示错误，我没有找到任何解决方案插入从这个方法我正在读取excel文件并存储到列表

public List collect(Receiver rec)
    {
        //ReadFromExcel rd = new ReadFromExcel();
        List<String> up = new ArrayList<String>();
        //List<String> details = rd.reader();
        //System.out.println(details);
        try( InputStream fileToRead = new FileInputStream(new File(rec.getFilePath()))) 
        { 
            XSSFWorkbook  wb = new XSSFWorkbook(fileToRead);


            wb.setMissingCellPolicy(Row.MissingCellPolicy.RETURN_BLANK_AS_NULL);
            XSSFSheet sheet = wb.getSheetAt(0);
            DataFormatter fmt = new DataFormatter();
            String data ="";
            for(int sn = 0;sn<wb.getNumberOfSheets()-2;sn++)
            {
                sheet = wb.getSheetAt(sn);
                for(int rn =sheet.getFirstRowNum();rn<=sheet.getLastRowNum();rn++)
                {
                    Row row = sheet.getRow(rn);
                    if(row == null)
                    {
                        System.out.println("no data in row ");

                    }
                    else
                    {
                        for(int cn=0;cn<row.getLastCellNum();cn++)
                        {
                            Cell cell = row.getCell(cn);
                            if(cell == null)
                            {
//                                System.out.println("no data in cell ");
//                                data = data + " " + "|";

                            }
                            else
                            {
                                String cellStr = fmt.formatCellValue(cell);
                                data = data + cellStr + "|";
                            }
                        }
                    }
                }
            }
            up = Arrays.asList(data.split("\\|"));


           // System.out.println(details);             
                }
                catch (FileNotFoundException ex) 
                {
                Logger.getLogger(BImplementation.class.getName()).log(Level.SEVERE, null, ex);
                } 
            catch (IOException ex) 
            {
                Logger.getLogger(BImplementation.class.getName()).log(Level.SEVERE, null, ex);
            } 

        Iterator iter = up.iterator();
        while(iter.hasNext())
        {
            System.out.println(iter.next());
        }

        String row="";
        Receiver info = null;
        String cid = "";
        String cname = "";
        String address = "";
        String mid = "";
        boolean b = false;


        List<Receiver> res = new ArrayList<Receiver>();
        int c = 0;
        try
        {
            String str = Arrays.toString(up.toArray()); 
           //System.out.println(str);
            String s = "";
            s = s + str.substring(1,str.length());
          // System.out.println("S:"+s);
            StringTokenizer sttoken = new StringTokenizer(s,"|");
            int count = sttoken.countTokens();
            while(sttoken.hasMoreTokens())
            {  
                if(sttoken.nextToken() != null)
                {
//                    System.out.print(sttoken.nextToken());
                    cid = sttoken.nextToken();
                    cname = sttoken.nextToken();
                    address = sttoken.nextToken();
                    mid = sttoken.nextToken();


                info = new Receiver(cid,cname,address,mid);
                res.add(info);
               System.out.println("cid :"+cid+ "  cname : "+cname +"  address : "+address+" mid : "+mid);
                c = res.size();
            // System.out.println(c);
                }
                else
                {
                    break;

                }
            }
            System.out.println(count);
           // System.out.println("s");



        } 
            catch(NoSuchElementException ex)
            {
                System.out.println("No Such Element Found Exception" +ex);
            }
        return up;

        }

用这种方法我试图插入数据库

public boolean insert(List res) 
    {
        String sqlQuery = "insert into records(c_id) values (?)";
        DBConnection connector = new DBConnection();

        boolean flag = false;

//        Iterator itr=res.iterator();
//        while(it.hasNext())
//        {
//            System.out.println(it.next());
//        }
         try( Connection con = connector.getConnection();)
         {
             con.setAutoCommit(false);        
             PreparedStatement pstmt = con.prepareStatement(sqlQuery);

              Iterator it = res.iterator();
              while(it.hasNext())
              {
                Receiver rs =(Receiver) it.next();
                pstmt.setString(1,rs.getcID());            
                pstmt.setString(2,rs.getcName());
                pstmt.setString(3,rs.getAddress());
                pstmt.setString(4,rs.getMailID());
                pstmt.addBatch();  


              }      
              int [] numUpdates=pstmt.executeBatch();
              for (int i=0; i < numUpdates.length; i++) 
              {
                if (numUpdates[i] == -2)
                {
                  System.out.println("Execution " + i +": unknown number of rows updated");
                  flag=false;
                }
                else
                {
                  System.out.println("Execution " + i + "successful: " + numUpdates[i] + " rows updated");
                  flag=true;
                }
              }
              con.commit();
            } catch(BatchUpdateException b) 
            {
              System.out.println(b);
              flag=false;
            }       
            catch (SQLException ex) 
            { 
                Logger.getLogger(BImplementation.class.getName()).log(Level.SEVERE, null, ex);
                System.out.println(ex);
                flag=false;
            }
return flag;      
        }

我想使用JDBC批量插入将列表对象插入到数据库中。

Answer 1

您的方法collect（Receiver rec）返回调用的字符串列表。

return up;

但是（如果您确实使用方法collect将List传递给insert（List res）方法），那么您希望此列表包含Receiver对象。这是不正确的，因为它收集（..）返回字符串列表。

当你试图转换Receiver rs =（Receiver）it.next（）时会导致错误;

您需要检查并修复代码，因此您将传递Receiver对象列表而不是字符串。

我真的建议你在任何使用List类的地方开始使用Generics。在这种情况下，编译器将立即显示所有数据类型错误。