Question

我需要这个程序的帮助。我正在尝试将列表值添加到Map中的现有键。请找到以下程序。请告诉我我错在哪里以及如何做。 `

  public class UpStreamFileCount
      {


   public static void main(String[] args) throws Exception 
   {
    String App_code = args[0];
    String App_Ctry_code = args[1];
    String hostname=null;
    Map<List<String>, List<FC>> fileNeedCheck = new HashMap<List<String>, List<FC>>();
    try
    {
        InetAddress inetAddress = InetAddress.getLocalHost();
        hostname=inetAddress.getHostName();
    }
    catch(UnknownHostException unknownHostException)
    {
        unknownHostException.printStackTrace();
     }

    BatchDateCalculation cmd = new BatchDateCalculation ();

    String Batch_date = cmd.Compare();
    Date currTime = cmd.CurrTime();
    Date timeBeforeOnehour = cmd.BeforOneHour();

    Pattern pattern = Pattern.compile(",");
    try (BufferedReader in = new BufferedReader(new FileReader("FC.csv"));)
    {
         Map<List<String>,List<FC>> grouped = in
                                             .lines()
                                             .skip(1)
                                             .map(line -> {
                                             String[] arr = pattern.split(line);
                                             return new  FC(arr[0],
                                                               arr[1],
                                                               arr[2],
                                                               arr[3],
                                                               arr[4],
                                                               arr[5]);
                                             })
                                             .collect(Collectors.groupingBy(x -> {
                                              return new ArrayList<String>(Arrays.asList(x.getUpstreamAppCode(), x.getUpstreamGrpAppCode()));
                                             })); 

         File data = new File("newFile.txt");
         if (data.exists()) 
         {
            data.delete();
         }

        FileWriter fw = new FileWriter(data,true);

        for(Map.Entry<List<String>,List<FC>> entry : grouped.entrySet() )
        {        
            List<String> list1 =  entry.getKey();
            for(FC  value : entry.getValue() )
            {
                String a = value.getSlaTime() ;
                Date newTime = cmd.covertTimeToDate(a);

                if (timeBeforeOnehour.before( newTime ) && currTime.after(newTime)) 
                {
                    String result  = String.join(",", list1);
                    String[] parts = result.split(",");
                    String part1 = parts[0];
                    String part2 = parts[1];
                    String path = value.getPath();
                    String stagPath = value.getStagPath();
                    String file = value.getFile();
                    String s = result + "," + path + "," + stagPath + "," + file + "," + a ;
                    String addMapValue = path  + "," + stagPath + "," + file + "," + a ;
                    fw.write(s);
                    fw.write(System.getProperty( "line.separator" ));
                    if(!fileNeedCheck.containsKey(list1))
                    {
                        fileNeedCheck.put(list1,Arrays.asList( new FC(part1,part2,path,stagPath,file,a)) );
                    }
                    else
                    {
                        List<FC> t = new ArrayList<String>(Arrays.asList(new FC(part1,part2,path,stagPath,file,a)));
                        t.add(value);
                        fileNeedCheck.get(list1).put(t);
                    }   
                }
            }
         }
        fw.close();
    }
      `

问题在于： - 在代码的else部分。请告诉我如何做到这一点

  if(!fileNeedCheck.containsKey(list1))
                    {
                        fileNeedCheck.put(list1,Arrays.asList( new FC(part1,part2,path,stagPath,file,a)) );
                    }
                    else
                    {
                        List<FC> t = new ArrayList<FC>(Arrays.asList(new FC(part1,part2,path,stagPath,file,a)));
                        t.add(value);
                        fileNeedCheck.get(list1).add(value);
                       // fileNeedCheck.get(list1).put(t);
                    }

我收到以下错误： -

＆GT;

   Exception in thread "main" java.lang.UnsupportedOperationException
   at java.util.AbstractList.add(AbstractList.java:148)
   at java.util.AbstractList.add(AbstractList.java:108)
   at java.util.AbstractCollection.addAll(AbstractCollection.java:344)
  at UpStreamFileCount.main(UpStreamFileCount.java:107)

Answer 1

当您的代码尝试将新元素添加到由Arrays.asList()从数组创建的列表时，会发生异常。此方法生成固定大小的列表，并且无法向其添加新元素。有关详细说明，请参阅javadoc of asList()。

解决此问题的一种简单方法是使用ArrayList（或List的其他实现），并使用从Arrays.asList()调用获得的列表对其进行初始化。

从您发布的堆栈跟踪中我假设它是您在此处作为值放入的列表： fileNeedCheck.put(list1,Arrays.asList( new FC(part1,part2,path,stagPath,file,a)) );

将此更改为： fileNeedCheck.put(list1, new ArrayList<FC>(Arrays.asList(new FC(part1,part2,path,stagPath,file,a))));

在java中的List <class>中为现有键添加值

1 个答案: