Java将新列追加到csv文件

Question

我想计算一些列数据并将其csv作为列写入文件。然后，在计算了另一列数据之后，我想将其附加到同一文件中，但作为新列。

这是我所做的：

try {
    FileWriter writer = new FileWriter(OUT_FILE_PATH, true);
    for (int i=0; i<data.size(); i++) {
        writer.append(String.valueOf(data.get(i)));
        writer.append(",");
        writer.append("\n");
    }
    writer.flush();
    writer.close();
} catch (Exception e) {}

结果-它将新列追加到第一列下方，因此我只有一个长列。

谢谢，

Answer 1

您将必须逐行读取文件，然后将新列插入每一行。这是使用BufferedReader和BufferedWriter的解决方案

public void addColumn(String path,String fileName) throws IOException{
    BufferedReader br=null;
    BufferedWriter bw=null;
    final String lineSep=System.getProperty("line.separator");

    try {
        File file = new File(path, fileName);
        File file2 = new File(path, fileName+".1");//so the
                    //names don't conflict or just use different folders

        br = new BufferedReader(new InputStreamReader(new FileInputStream(file))) ;
        bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file2)));
        String line = null;
                    int i=0;
        for ( line = br.readLine(); line != null; line = br.readLine(),i++)
        {

            String addedColumn = String.valueOf(data.get(i));
            bw.write(line+addedColumn+lineSep);
    }

    }catch(Exception e){
        System.out.println(e);
    }finally  {
        if(br!=null)
            br.close();
        if(bw!=null)
            bw.close();
    }

}