我有以下代码：

public static void main(String[] args) throws IOException {
        //File being read:
        String fileName = "src/data/Belgium.csv";


    String[] nextLine;

    try (CSVReader reader = new CSVReader(new FileReader(fileName),','"',1)) {


        while ((nextLine = reader.readNext()) != null) {

            for (String line : nextLine) {
                //NewFile
                //When 2nd parameter - ture,it gets so big,that excel can't handle it anymore...
                FileWriter writer = new FileWriter("src/dataNew/BelgiumNew1.csv",true);

                line = line.replaceAll("T"," ");
                line = line.replaceAll("Z","");
                line = line.replaceAll("ActualGenerationPerUnit.mean","");
                line = line.replaceAll("Plantname:","");
                //Escaping curly braces is a must!
                line = line.replaceAll("\\{","");
                line = line.replaceAll("\\}","");

                writer.append(line);
                writer.flush();
                writer.close();

                System.out.println(line);
            }
        }System.out.println("Successfully written");
    }
}

在控制台中，使用System.out.println（line）输出的代码为我提供了正确的输出。但是，当我打开CSV文件时，它似乎是反向写入的。Excel首先抱怨行数。但是，仅显示原始数据集的最后一行。数据集（以一种低效的方式进行了预处理）包含1000多个行。因此，我不能简单地附加每个条目。

有更好的方法吗？

提示和技巧非常受欢迎。更进一步，我尝试了一些编写器：-CSVwrite-BufferedWriter-FileWriter

还检查了Stackoverflow上的其他问题…似乎无法使其正常工作。谢谢！

更新：

问题得到解答！最终代码：

 public static void main(String[] args) throws IOException {
    //File being read:
    String fileName = "src/data/Belgium.csv";

    //When 2nd parameter - ture,that excel can't handle it anymore...
      FileWriter writer = new FileWriter("src/dataNew/BelgiumNew5.csv",true);


    String[] nextLine;

    try (CSVReader reader = new CSVReader(new FileReader(fileName),1)) {

        while ((nextLine = reader.readNext()) != null) {

            for (String line : nextLine) {

                line = line.replaceAll("T","");

                writer.append(line);
                writer.append(System.lineSeparator());
                System.out.println(line);


            }
        }System.out.println("Successfully written");
        }catch(Exception e){
        e.printStackTrace();
    }finally {
        if (writer != null){
            writer.flush();
            writer.close();
        }
    }
}

private void WritetoCsvFile()
{
    var us = users.ElementAt(0);
    string names = "Number',";
    string userAnswer = (us.userName + ",");
    foreach (string ss in user)
    {
        string str = Path.GetFileName(ss);
        names = names + str + ",";
    }
    foreach (string ans in us.answer)
    {
        userAnswer = userAnswer + ans + ",";
    }

    using (StreamWriter sw = new StreamWriter("EntranceLog.csv"))
    {
        sw.WriteLine(names);
        sw.WriteLine(userAnswer);

    }

    this.Close();
}

解决方法

using (StreamWriter sw = new StreamWriter("EntranceLog.csv",true))

/// <summary>
        /// 写入数据到CSV文件，覆盖形式
        /// </summary>
        /// <param name="csvPath">要写入的字符串表示的CSV文件</param>
        /// <param name="LineDataList">要写入CSV文件的数据，以string[]类型List表示的行集数据</param>
        public static   void OpCsv(string csvPath, List<string[]> LineDataList)
        {
            using (FileStream fs = new FileStream(csvPath.Trim(), FileMode.OpenOrCreate, FileAccess.ReadWrite))
            {
                using (StreamWriter sw = new StreamWriter(fs, Encoding.Default))
                {
                    StringBuilder sb_csvStr = new StringBuilder();
                    for (int i = 0; i < LineDataList.Count; i++)//<--row
                    {
                        sb_csvStr.Clear();
                        for (int j = 0; j < LineDataList[i].Length; j++)//<--col
                        {
                            sb_csvStr.Append(string.Format("{0},", LineDataList[i][j].ToString()));
                        }
                        sw.WriteLine(sb_csvStr.ToString().Substring(0, sb_csvStr.ToString().Length - 1));
                    }
                    fs.Flush();
                }
            }
        }

/// <summary>
        /// 读取csv文件
        /// </summary>
        /// <param name="csvPath">string 标识的 csv文件路径</param>
        /// <returns>返回的读取的 csv 文件的行集合</returns>
        public static string[] ReadCsv(string csvPath)
        {
            string[] csvLineList = File.ReadAllLines(csvPath, Encoding.Default);
            return csvLineList;
        }    

1 fo=open("city.csv","r")#打开命名为city的CSV文件
2 ls=[] #定义一个空列表，将CSV中读取的文件放进列表
3 for line in fo:
4     line=line.replace("\n","")
5     ls.append(line.split(","))
6 print(ls)
7 fo.close()#关闭文件

[[''城市'', ''环比'', ''同比'', ''定基''], [''北京'', ''101.5'', ''120.7'', ''121.4''], [''上海'', ''101.2'', ''127.3'', ''127.8''], [''广州'', ''101.3'', ''119.4'', ''120.0''], [''深圳'', ''102.0'', ''140.9'', ''145.5''], [''沈阳'', ''100.1'', ''101.4'', ''101.6''], ['''', '''', '''', '''']]

 1 fo=open("city.csv","r")#打开命名为city的CSV文件
 2 ls=[]#定义一个空列表，将CSV中读取的文件放进列表
 3 for line in fo:
 4     line=line.replace("\n","")
 5     ls=line.split(",")
 6     lns=""
 7     for s in ls:
 8         lns+="{}\t".format(s)
 9     print(lns)
10 fo.close()

城市    环比    同比    定基    
北京    101.5    120.7    121.4    
上海    101.2    127.3    127.8    
广州    101.3    119.4    120.0    
深圳    102.0    140.9    145.5    
沈阳    100.1    101.4    101.6

1 fo=open("city.csv","w")
2 ls=[''湖北'',''101.2'',''120.7'',''121.4'']
3 fo.write(",".join(ls)+"\n")
4 fo.close()

 1 fr=open("city1.csv","r")
 2 fw=open("city1out.csv","w")
 3 ls=[]
 4 for line in fr:#将CSV文件当中的二维数据读到列表当中去
 5     line=line.replace("\n","")
 6     ls.append(line.split(","))
 7 for i in range(len(ls)):#遍历列表变量计算百分数
 8     for j in range(len(ls[i])):
 9         if ls[i][j].replace(".","").isnumeric():
10             ls[i][j]="{:.2}%".format(float(ls[i][j])/100)
11 for row in ls:#将列表变量中的两位数据写入CSV文件当中去
12     print(row)
13     fw.write(",".join(row)+"\n")
14 fr.close()
15 fw.close()