如何在Java中将ArrayLists列表写入CSV格式 [英] How to write a List of ArrayLists to CSV format in Java

问题描述

我有以下格式的数据：

  List< ArrayList< String> 
  

我想将它写入CSV。下面是我的代码：

  private void void writeToCSV（List< ArrayList< String>> csvInput）throws IOException {
 
 String csv =C：\\output.csv; 
 CSVWriter writer = null; 
 
 try {
 writer = new CSVWriter（new FileWriter（csv））; 
} catch（IOException e）{
 // TODO自动生成的catch块
 e.printStackTrace（）; 
} 
 
 for（ArrayList< String> each：csvInput）{
 writer.writeNext（each）; 
} 
 
 
 writer.close（）; 
} // end of writeTOCSV 
  

方法writeNext只允许String []它的参数。当我试图使用一个Object []类型转换'ArrayList each'到String []如下所示，我得到运行时类型转换错误：

  Object [] eachTemp = each.toArray（）; 
 writer.writeNext（（String []）eachTemp）; 
  

有人可以告诉我我在哪里出错吗？

Object [] 转换为 String [] 因为 Object [] 可以包含Dog，Cat，Integer等。

href =http://docs.oracle.com/javase/7/docs/api/java/util/List.html#toArray%28T[]%29 =nofollow> list＃toArray（T [] ）方法。

  List< String> list = new ArrayList< String>（）; 
 String [] array = list.toArray（new String [] {}）; 
  

I have data in the below format:

   List<ArrayList<String>>

I want to write it to CSV. Below is my code:

private static void writeToCSV(List<ArrayList<String>> csvInput) throws IOException{

String csv = "C:\\output.csv";
CSVWriter writer = null;

try {
    writer = new CSVWriter(new FileWriter(csv));
    } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }

for(ArrayList<String> each: csvInput){
    writer.writeNext(each);
}


writer.close();
}//end of writeTOCSV

The method 'writeNext' allows only String[ ] as it's argument. When I try to type cast 'ArrayList each' into String[] using an Object[ ] as shown below, I am getting run time type casting error:

   Object[] eachTemp = each.toArray();
   writer.writeNext((String[]) eachTemp);

Could anyone please tell me where I am going wrong?

解决方案

You can't cast Object[] into String[] because Object[] can contains Dog, Cat, Integer etc.

you should use overloaded List#toArray(T[]) method.

List<String> list = new ArrayList<String>();
String[] array = list.toArray(new String[] {});

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