使用Filewriter将新文件写入CSV文件

Question

I am working on a CSV file having 45312 instances(row) and 8 attributes. I want to modify (using some mathematical operation) the input csv file and write it. To modify the CSV I have extracted each column value (v="comma separated position") from every instance(row) and then try to modify it. But I am facing the problem here that when the for loop moves to next iteration (like v=3 from v=2) then all modified instance values from the previous iteration (v=2) are reverted back to their original state. At the end I want the new CSV file with all modifications processed.

    import java.io.File;
    import java.io.FileNotFoundException;
    import java.io.FileWriter;
    import java.io.*; 
    public class Normalization {
     public static void main(String[] args)throws IOException {
            String filename = "abc.csv";
            File file = new File(filename);
            BufferedWriter writer = null;
    try{           
             writer = new BufferedWriter(new   FileWriter("lyupdated.csv"));      
        for (int v = 1; v < 8; v++)
        {
                Scanner inputStream = new Scanner(file);
          while (inputStream.hasNext())
          {
                String data = inputStream.next();         
                String[] values = data.split(",");
                double balance = Double.parseDouble(values[v]);
                balance=balance*10;//for mathoperation code simplification
                values[v] = String.valueOf(balance);      
                // iterate through the values and build a string out of them
                StringBuilder sb = new StringBuilder();
                //  String newData = sb.toString();
               for (int i = 0; i < values.length; i++) {
                        sb.append(values[i]);
                        if (i < values.length - 1) {
                            sb.append(",");
                        }
                    }
          System.out.println(sb.toString());
          writer.write(sb.toString()+"\n");
           }inputStream.close();           
        } writer.close();
     }
          catch (FileNotFoundException ex) {
                Logger.getLogger(Normalization.class.getName()).log(Level.SEVERE, null, ex);
            }
    }
    }

Answer 1

Your code doesn't make much sense. You need to open the file, have a loop to read the file line by line, and split each line into 8 columns.

But instead, look at what you have:

for (int v = 1; v < 8; v++) {
    Scanner inputStream = new Scanner(file);

So,

• you don't loop over all the lines of the file, but over 7 columns
• at each of the 7 iterations, you open a new Scanner over the file, thus always reading from the start of the file

As Tom says in his comment, use a library dedicated to CSV file parsing and generation. It will have the following advantages:

• being correct
• being tested by many developers, and optimized
• offering a higher-level API
• handling escaping of values correctly