Adding value to existing key in List in java

Question

I need a help in this program. I am trying to add list value to existing key in Map. Please find below program. Kindly let me know where I am wrong and how I can do. `

  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();
    }
      `

The issue is here: - in the else part of the code . Please let me know how I can do this

  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);
                    }   

I am getting the error below:-

>

   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

The exception occurs when your code tries to add a new element to a list created by Arrays.asList() from an array. This method produces a fixed-size list and new elements can not be added to it. See javadoc of asList() for further explanation.

An easy way to fix this is to use an ArrayList (or other implementation of List) instead, and initialize it with the list obtained from Arrays.asList() call.

From the stack traces you posted I assume it's the list you put as a value to the map here: fileNeedCheck.put(list1,Arrays.asList( new FC(part1,part2,path,stagPath,file,a)) );

Change this to: fileNeedCheck.put(list1, new ArrayList<FC>(Arrays.asList(new FC(part1,part2,path,stagPath,file,a))));