A simple command line application in Java to handle todo list

TodoApp.java

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.Serializable;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;

public class TodoApp {

  public static void main(String[] ignored) throws ParseException, IOException, ClassNotFoundException {
    System.out.println("-------------------");
    System.out.println("This is a simple and easy to use todo app.");
    System.out.println("Type 'help' to know how to use this app.");
    System.out.println("-------------------");

    Tree tree = new Tree("/tmp/todos.tree.db");

    System.out.println("What do you want to do? See 'help' for a list of available options.\n");
    while(true){
      System.out.printf("> ");
      BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
      String argsString = reader.readLine();
      String[] args = argsString.split(" ");

      if (args.length < 1){
        System.out.printf("Please provide at least one argument or type 'help' for more detail.");
        return;
      }
      String firstArg = args[0];

      if ("add_container".equals(firstArg)) {
        // add_container "id" "title"
        if (args.length < 3){
          System.out.printf("Add a container requires an id and a title");
          continue;
        }
        int id = Integer.parseInt(args[1]);
        String title = args[2];
        tree.findAndAddTodo(new Container(title), id);
        System.out.println("Done adding a container : " + title + " to id: " + id);
      } else if ("add_item".equals(firstArg)) {
        // add_item "id" "title"
        if (args.length < 3){
          System.out.printf("Add an item requires a container id and a title");
          continue;
        }
        int id = Integer.parseInt(args[1]);
        String title = args[2];
        tree.findAndAddTodo(new Item(title), id);
        System.out.println("Done adding item: " + title + " to id: " + id);
      } else if ("delete".equals(firstArg)){
        // delete "id"
        if (args.length < 2){
          System.out.printf("Delete a container requires a container id");
          continue;
        }
        int id = Integer.parseInt(args[1]);
        tree.findAndDeleteTodo(id);
        System.out.println("Done deleting a todo id: " + id);
      } else if("list".equals(firstArg)){
        System.out.println(tree.printTree());
      } else if("save".equals(firstArg)){
        tree.save();
      } else if("load".equals(firstArg)){
        tree = tree.load();
      } else if("help".equals(firstArg)){
        help();
      } else if("exit".equals(firstArg)){
        System.out.println("Thank you for using the simple todo application. Exiting..");
        System.exit(1);
      } else {
        System.out.printf("Unknown argument: " + firstArg);
        System.out.println(". Please take a look at the supported arguments at\n");
        help();
      }
    }
  }

  public static void help(){
    System.out.println("- help                          : This help message");
    System.out.println("- list                          : List all the items/containers of your todo list");
    System.out.println("- save                          : Save the data to a local temporary file");
    System.out.println("- load                          : Load the data from a local temporary file");
    System.out.println("- add_item <ID> <NAME>          : Add an item/container to your todo list");
    System.out.println("  <ID> = 0 if you want to add to the root level, otherwise, use " +
                                   "the <ID> of a container you want to add to");
    System.out.println("  <NAME> (String) Is the name of the item you want to add. The " +
                                    "string cannot contain empty 'spaces'. For example, 'some item' " +
                                    "is not acceptable.");
    System.out.println("For example, to add an item named buy_milk to the root level, do: ");
    System.out.println(" add_item 0 buy_milk");
    System.out.println("");
    System.out.println("- add_container <ID> <NAME>     : Add an item/container to your todo list");
    System.out.println("  <ID> = 0 if you want to add to the root level, otherwise, use " +
                                    "the <ID> of a container you want to add to");
    System.out.println("  <NAME> (String) Is the name of the item you want to add. The " +
                                    "string cannot contain empty 'spaces'. For example, 'some item' " +
                                    "is not acceptable.");
    System.out.println("");
    System.out.println("- delete <ID>                   : Delete a container / item using an ID");
    System.out.printf("\n\n");
  }

  public static class Tree implements Serializable {

    /**
     * The data is serialized and stored in this file.
     */
    private String saveLocation = "/tmp/todos.db";

    /**
     * The tree always has a root
     */
    private Container root = new Container("");

    public Tree(String saveLocation){
      this.saveLocation = saveLocation;
    }

    public Tree findAndAddTodo(TodoAbstract todo, int id){
      if (id == 0){
        root.add(todo);
      } else {
        root.findAndAddContainer(todo, id);
      }

      return this;
    }

    public Tree findAndDeleteTodo(int id){
      if (id == 0){
        System.out.printf("Can't delete the root");
        return this;
      } else {
        root.findAndDeleteTodo(id);
      }

      return this;
    }

    public String toString(){
      return root.toString();
    }

    public String printTree(){
      return recursivePrint(root, 0);
    }

    private String recursivePrint(TodoAbstract node, int level){
      String result = "";
      String indent = "";
      for(int i = 0; i < level; i++){
        indent += "   ";
      }

      result += indent + "-" + node.getClass().getSimpleName() + "[id]=" + node.id + "\n";
      result += indent + "(todo): " + node.title + "\n";

      if (node.getClass() == Container.class){
        for (Map.Entry<Integer, TodoAbstract> n : ((Container) node).todos.entrySet()){
          result += recursivePrint(n.getValue(), level + 1);
        }
      }

      return result;
    }

    public Tree load() throws IOException, ClassNotFoundException {
      Path path = Paths.get(saveLocation);
      byte[] array = Files.readAllBytes(path);
      ByteArrayInputStream bis = new ByteArrayInputStream(array);
      ObjectInput in = null;

      try {
        in = new ObjectInputStream(bis);
        return (Tree) in.readObject();
      } finally {
        try {
          bis.close();
        } catch (IOException ex) {
          // ignore close exception
        }
        try {
          if (in != null) {
            in.close();
          }
        } catch (IOException ex) {
          // ignore close exception
        }
      }
    }

    public void save() throws IOException {
      OutputStream file = new FileOutputStream(saveLocation);
      ByteArrayOutputStream bos = new ByteArrayOutputStream();
      ObjectOutput out = null;
      try {
        out = new ObjectOutputStream(bos);
        out.writeObject(this);
        file.write(bos.toByteArray());
      } finally {
        try {
          if (out != null) {
            out.close();
          }
        } catch (IOException ex) {
          // ignore close exception
        }
        try {
          bos.close();
        } catch (IOException ex) {
          // ignore close exception
        }
      }
      file.close();
    }
  }

  public static class Container extends TodoAbstract {
    public Map<Integer, TodoAbstract> todos = new HashMap<>();

    public Container(String title){
      super(title);
    }

    public Container add(TodoAbstract todo){
      todos.put(todo.id, todo);
      return this;
    }

    public Container delete(int id){
      todos.remove(id);
      return this;
    }

    public Container findAndAddContainer(TodoAbstract todo, int id){
      if (this.id != id){
        for(Map.Entry<Integer, TodoAbstract> n : todos.entrySet()){
          if (n.getValue().getClass() == Container.class){
            ((Container)n.getValue()).findAndAddContainer(todo, id);
          }
        }
      } else {
        add(todo);
      }

      return this;
    }

    public Container findAndDeleteTodo(int id) {
      if (todos.containsKey(id)) {
        todos.remove(id);
      } else {
        for (Map.Entry<Integer, TodoAbstract> n : todos.entrySet()) {
          if (n.getValue().getClass() == Container.class) {
            ((Container) n.getValue()).findAndDeleteTodo(id);
          }
        }
      }

      return this;
    }

    public String toString(){
      return todos.toString();
    }
  }

  public static class Item extends TodoAbstract {
    public Item(String title) {
      super(title);
    }
  }

  public static abstract class TodoAbstract implements Todo, Serializable {
    protected final int id;
    protected String title;

    public TodoAbstract(String title){
      this.id = UUID.randomUUID().hashCode();
      this.title = title;
    }

    public String toString(){
      return "{ type: " + getClass().getSimpleName() +
          ", id: " + id +
          ", title: " + title + "}";
    }
  }

  interface Todo {

  }
}