BufferedWriter is not writing contents of Map to text file; Minecraft server

I have PVPStats objects stored in PlayerMeta.java:

public static Map <UUID, PVPstats> sPVPStats = new HashMap<>();

I know for sure the map is getting populated with objects that contain the expected vars for each uuid.

I'm trying to write these objects (converted to single lines of strings) into plugins/core/killstats.txt when the server calls onDisable() in Main.java

Along with the Map object, in PlayerMeta.java are also the methods to update and retrieve PVPStats objects from the Map. Those are all working.

The part that is not is working is the write method:

public static void writePVPStats() throws IOException {
        
        BufferedWriter w = new BufferedWriter(new FileWriter("plugins/core/killstats.txt"));
        
        sPVPStats.keySet().forEach(user -> {            
            try {
                System.out.println(sPVPStats);
// stdout = {a6b6e3a1-a1ec-4fee-9d6d-f5e495c3e9d7=a6b6e3a1-a1ec-4fee-9d6d-f5e495c3e9d7:1:0}
                
                w.write(user.toString() + "\n");
                w.flush();
                
              } catch (IOException e) {
                  throw new UncheckedIOException(e);
              }
        });
        w.close();
    }

kill.txt after onDisable() is done:

a6b6e3a1-a1ec-4fee-9d6d-f5e495c3e9d7

Instead it needs to be:

{a6b6e3a1-a1ec-4fee-9d6d-f5e495c3e9d7=a6b6e3a1-a1ec-4fee-9d6d-f5e495c3e9d7:1:0}

For reference, here is the complete PVPStats class.

Lastly, in case it matters / helps, the reader on server launch:

Files.readAllLines(killstats_user_database.toPath()).forEach(line -> {
            PVPstats stats = PVPstats.fromString(line);
            PlayerMeta.sPVPStats.put(stats.playerid, stats);
        });

Source Code:

backend.FileManager.java

backend.PlayerMeta.java

backend.PVPstats.java

events.PVP.java

EDIT

I just tried this with killstats.txt file type nad killstats.txt doesnt have anything in it now.

public static void writePVPStats() throws IOException {
        
        BufferedWriter w = new BufferedWriter(new FileWriter("plugins/core/killstats.txt"));
        
        for (PVPstats object: sPVPStats.values()) {
            try {
                System.out.println(sPVPStats);
                
                w.write(object.toString() + "\n");
                w.flush();
                
              } catch (IOException e) {
                  throw new UncheckedIOException(e);
              }
        };
        w.close();
    }

Ok so there were multiple issues. I wasn't controlling the flushing of the buffer, I declared the hasmap incorrectly, I wasn't accessing the value part of the hash map, and I wasn't correctly enforcing plain text.

SOLUTION

public static Map <UUID, PVPstats> sPVPStats = new HashMap<UUID, PVPstats>();

    public static void writePVPStats() throws IOException {
        
        BufferedWriter w = new BufferedWriter(new FileWriter("plugins/core/killstats.txt"));
        
        for (PVPstats object: sPVPStats.values()) {
            try {
                System.out.println(sPVPStats);
                System.out.println(object.toString());
                
                w.write(object.toString() + "\n");
                w.flush();
                
              } catch (IOException e) {
                  throw new UncheckedIOException(e);
              }
        };
        w.close();
    }