OpenCSV-在添加列时将一个csv文件复制到另一个 [英] OpenCSV - copying one csv file to another while adding a column

问题描述

我正在尝试使用OpenCSV读取一个CSV文件.然后，我想从输入的csv复制所有数据并将其输出到另一个csv文件，同时添加带有信息的新列.

I am trying to read from one CSV file using OpenCSV. I then want to copy all the data from the input csv and output it to another csv file while adding a new column with information.

public void run_streets_tsv( String tsvIn, String tsvOut) throws Exception
{

    CSVReader reader = null; 
    CSVWriter writer = null;

    try
    {

        reader = new CSVReader((new FileReader(tsvIn)));
        writer = new CSVWriter(new FileWriter(tsvOut), '\t');

        String element [] = null;
        List<String[]> a = new ArrayList<String[]>();

        while((element = reader.readNext()) != null){
            for(int i = 0; i<element.length; i++){
                a.add(i, element);
                //a.add("JSON");  need to add this json element at the end of each column 
            }
        }
        writer.writeAll(a);
    }
    catch(Exception e)
    {
        throw e;
        } 
    finally
    {
        reader.close();
        writer.close();
        }
    }

我正在尝试的另一种方法是这样的(更改while循环，所有其他代码保持不变):

Another method I am trying is like this (changing the while loop, all other code remains the same):

        String element [] = null;
        while((element = reader.readNext()) != null){
            ArrayList list = new ArrayList(Arrays.asList(reader));
            list.add(element);
            list.add("JSON");
            writer.writeNext(element);
        }

这确实可以正确打印所有行，但只是复制而已.我想添加额外的"JSON"列及其数据.

This does correctly print all the lines, but it just copies. I want to add that extra "JSON" column with its data.

推荐答案

以下代码将 element -Array放大1，从而使您可以在新创建的最后一个索引中放入内容.然后只需保存该数组即可.

The following "enlarges" the element-Array by one, enabling you to put something in the newly created last index. Then just save that array.

import java.util.Arrays;

    String element[] = null;
    while((element = reader.readNext()) != null){
        element = Arrays.copyOf(element, element.length + 1);
        element[element.length - 1] = "JSON";
        writer.writeNext(element);
    }

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