java - 对 CSVRecords 列表进行排序 (apache commons)

Question

我得到了这个 CSV 文件:

User ID,First Name
3,David 
4,Ruby 
10,Ruby 

我想使用以下方法按升序排序:

@Override
    public void sort(InputStream in, OutputStream out, String field_name, Comparator<CSVRecord> comparator) throws IOException {

     Reader inputStreamReader = new InputStreamReader(in);  
     Iterable<CSVRecord> csvRecords = CSVFormat.RFC4180.withFirstRecordAsHeader().parse(inputStreamReader);

     List<CSVRecord> csvRecordsList = Lists.newArrayList(csvRecords);
     Collections.sort(csvRecordsList,comparator);

     Writer outputStreamWriter = new OutputStreamWriter(out);
     CSVPrinter cvsPrinter = CSVFormat.RFC4180.print(outputStreamWriter); 
     cvsPrinter.printRecords(csvRecordsList);
     cvsPrinter.flush();
     cvsPrinter.close();

问题是 Collections.sort 不执行任何操作。这是我作为参数提供的比较:

 Comparator<CSVRecord> comparator = (op1,op2) -> op2.get(field).compareTo(op1.get(field));

我做错了什么？

Answer 1

CSVRecord.get() 返回一个 String，因此您实际上调用的是 String.compareTo 而不是 Integer.compareTo 在你的比较器中。试试这个:

Comparator<CSVRecord> comparator = (op1,op2) -> Integer.valueOf(op2.get(field)).compareTo(Integer.valueOf(op1.get(field)));